Patent Publication Number: US-7900002-B2

Title: Multi-client cluster-based backup and restore

Description:
RELATED APPLICATION 
     This application claims priority to and is a divisional of U.S. patent application Ser. No. 11/407,798, filed Apr. 20, 2006, now U.S. Pat. No. 7,441,092 which is incorporated herein by reference. This application also references U.S. patent application Ser. No. 11/407,783 filed on Apr. 20, 2006, which is herein included by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This description relates generally to protecting against data loss and more specifically to cluster-based backup and restore technologies. 
     BACKGROUND 
     Backup has been an important aspect of computing since the invention of persistent memory systems, such as disk drives. With increasing data storage and personal computer (“PC”) usage trends, the need for backup solutions is growing in importance. Medium sized and large businesses can typically afford data protection solutions, such as backup systems, and have a wide range of choices and an entire industry available to support them. However, the technology and products available to the typical consumer, home based business, or small business for protecting against data loss has not advanced in step with these trends. Yet such users are doing more and more important work on their PCs, and storing more and more precious, irreplaceable data. At the same time the quality of PC hardware, particularly consumer grade hard drives seems to be declining, increasing the risk of data loss. 
     Historically data loss was protected against by backing up user data files. Backing up system files and application was commonly avoided to save backup storage space and time. After a failure, a user typically re-installed the PC&#39;s operating system and applications from the original disks in addition to restoring lost data files. As Internet usage via the PC has grown, new variations of data loss have developed. Down-loaded applications, for example, are becoming increasingly common—but it is also common for such applications to no longer be available when needed for a system restore. It is also increasingly common for a user to spend many hours setting up and configuring a PC—but it is uncommon for typical backup products to preserve every aspect of the PCs configuration. Thus, after restoring files following a system failure, the user is forced to spend the time required, again, to re-configure the PC to restore it to its pre-failure condition. 
     In addition to the significant time complete system restoration may take, common storage devices such as disk drives are becoming increasingly large in terms of storage capacity. It is now common for a new PC to include a disk drive with 200 GBs or more of storage space. A typical small office or home may have several such PCs. The amount of time and storage space required to create backups of these PCs using conventional mechanisms is often prohibitive. The amount of time required to restore from such backups may also be significant. 
     SUMMARY 
     The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later. 
     The present examples provide technologies for backing up and restoring digital information stored on devices using cluster-based backup methods, including devices on a network. 
     Many of the attendant features will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein: 
         FIG. 1  is a block diagram showing an example networking environment including a backup server and several clients coupled via a network. 
         FIG. 2  is a block diagram showing example backup space requirements with and without single-instance storage across clients. 
         FIG. 3  is a block diagram showing an example backup system including a backup engine and a client backup module and a client restore module, both modules coupled to the backup engine via a backup protocol. 
         FIG. 4  is a block diagram showing example protocol state transitions and messages for backup protocol session establishment and abort operations. 
         FIG. 5  is a block diagram showing a simplified example backup process for performing a cluster-based backup. 
         FIG. 6  is a block diagram showing example protocol state transitions and messages for performing a cluster-based backup operation during a protocol session. 
         FIG. 7   a  is a block diagram showing a continuation of example protocol state transitions and messages for performing a cluster-based backup operation. 
         FIG. 7   b  is a block diagram showing example protocol state transitions and messages for discovering client machines that have one or more backups in a backup server&#39;s database. 
         FIG. 8   a  is a block diagram showing example protocol state transitions and messages for discovering any backup sets for a particular machine that are stored in a backup server&#39;s database. 
         FIG. 8   b  is a block diagram showing example protocol state transitions and messages for discovering any volume configurations for a particular machine that are stored in a backup server&#39;s database. 
         FIG. 8   c  is a block diagram showing example protocol state transitions and messages for discovering any volume backups in a specific backup set for a particular machine that are stored in a backup server&#39;s database. 
         FIG. 8   d  is a block diagram showing example protocol state transitions and messages for establishing a backup schedule for a particular machine. 
         FIG. 9  is a block diagram showing example protocol state transitions and messages for restoring a particular machine. 
         FIG. 10  is a block diagram showing example phases of a 5 phased cluster-based backup operation. 
         FIG. 11  is a block diagram showing Phase  1  of an example cluster-based backup operation. 
         FIG. 12  is a block diagram showing Phase  2  of the example cluster-based backup operation. 
         FIG. 13  is a block diagram showing Phase  3  of the example cluster-based backup operation. 
         FIG. 14  is a block diagram showing Phase  4  of the example cluster-based backup operation. 
         FIG. 15  is a block diagram showing Phase  5  of the example cluster-based backup operation. 
         FIG. 16  is a block diagram showing an example commit operation for a backup operation. 
         FIG. 17  is a block diagram showing an example cluster-based restore operation for restoring a partial or complete backup from a backup server to a client. 
         FIG. 18  is a block diagram showing an example backup database including example data structures of which it is comprised. 
         FIG. 19  is an XML description showing the schema of an example Commit data structure. 
         FIG. 20  is an XML description showing the schema of an example Control data structure. 
         FIG. 21  is an XML description showing the schema of an example Machines data structure. 
         FIG. 22  is an XML description showing the schema of an example VolumeConfig data structure. 
         FIG. 23  is an XML description showing the schema of an example BackupSet data structure. 
         FIG. 24  is an XML description showing the schema of an example GlobalCluster data structure. 
         FIG. 25  is an XML description showing the schema of an example GlobalClusterLatest data structure. 
         FIG. 26  is an XML description showing the schema of an example Index data structure. 
         FIG. 27  is an XML description showing the schema of an example Data data structure. 
         FIG. 28  is an XML description showing the schema of an example Volume data structure. 
         FIG. 29  is an XML description showing the schema of an example FileRecordHash data structure. 
         FIG. 30  is an XML description showing the schema of an example VolumeCluster data structure. 
         FIG. 31  is an XML description showing the schema of an example VolumeClusterLatest data structure. 
         FIG. 32  is an XML description showing the schema of an example VolumeException data structure. 
         FIG. 33  is a block diagram showing example relationships between a portion of the per cluster-size data structures. 
         FIG. 34  is a block diagram showing example relationships between the per cluster-size data structures as shown in  FIG. 33  with the addition of a GlobalClusterLatest data structure. 
         FIG. 35  is a block diagram showing an example computing environment in which the technologies, processes, systems and methods described above may be implemented. 
     
    
    
     Like reference numerals are used to designate like parts in the accompanying drawings. 
     DETAILED DESCRIPTION 
     The detailed description provided below in connection with the appended drawings is intended as a description of the present invention and is not intended to represent the only forms in which the present invention may be constructed or utilized. The description sets forth example functions of the invention and example sequences of steps for constructing and operating the invention. However, the same or equivalent functions and sequences may be accomplished by different examples. 
     Although the present invention is described and illustrated herein as being implemented in a networking and computing environment, the environment described is provided as an example and not a limitation. As those skilled in the art will appreciate, the present invention is suitable for implementation in a variety of different types of networking and computing systems. 
       FIG. 1  is a block diagram showing an example networking environment  100  including a backup server  110  and several clients  120 ,  130 ,  140 , and  150  coupled via a network  102 . Backup server  110  and clients  120 ,  130 ,  140 , and  150  are each example devices such as the computing environment described in connection with  FIG. 35 , or the like. Such devices include, but are not limited to, computing systems, files servers, main frames, personal computers (“PCs”), laptop computers (“laptops”), tablet PCs, hand-held devices, portable devices, embedded devices, electronic devices, machines and systems including computing devices such as appliances, automobiles, etc., set-top boxes, or any device that includes some form of storage device that may benefit from the backup technologies described herein. Such devices typically include some form of file system that provides for creating, locating, accessing, and maintaining files, folders, directories, file system metadata, and the like. Such a file system may be part of an operating system and typically translates requests for file operations into low-level, sector- or cluster-oriented tasks that can be understood by the systems controlling a storage device. 
     Network  102  may be any type of communications mechanisms providing for communications between backup server  110  and other devices on the network, such as example devices  120 ,  130 ,  140 , and  150 . Example communications mechanisms include wired networks including Ethernet, Universal Serial Bus (“USB”), FireWire, power line communication (“PLC”), and the like, as well as wireless networks including those using radio frequency (“RF”), infrared (“iR”), fiber optics and other light-based mechanisms, microwave links and the like, and other wireless mechanisms. Other examples include local area networks (“LANs”), wide area networks (“WANs”), storage area networks (“SANs”), metropolitan area networks (“MANs”), virtual private networks (“VPNs”), the Internet, and the like. Network  102  may also include a hardware bus internal to a device enabling the device to communicate between its own internal mechanisms, elements, storage devices, memory, and the like. Further examples of network  102  and network environment  100  are provided in connection with example computing device  3501 , described in connection with  FIG. 35 . 
     Example devices  120 ,  130 ,  140 , and  150  (also referred to herein as “clients” and “machines”) as well as backup server  110  typically include, or are coupled to, some type of device or mechanism for storing digital information (“data”) for which backup protection may be desirable (not shown in  FIG. 1 ). Examples of such storage devices, including system memory and mass storage devices, are provided in connection with example computing device  3501 , described in connection with  FIG. 35 . Further examples include any form of data storage device or mechanism that may benefit from having its contents protected via backup. Another example storage device may include a plurality of devices, such as that provided by a redundant array of independent disks (“RAID”) or other array technologies or the like. 
     A storage device is also referred to herein as a “volume”. A storage device such as a disk drive or the like may also be divided or “partitioned” into several volumes, each volume comprising a portion of the overall storage space of the storage device with each volume capable of being considered independently of the whole storage device and any other volumes on the storage device. Data stored on a volume is typically stored in a “file” or the like. Files are typically contained in folders, also commonly known as directories. 
     The term “backup”, as used herein, refers to a copy of data, the copy existing in some form such that the original data can be restored, reconstructed, re-created, or the like, from the copy. Such data may include, but is not limited to, computer programs, applications, files, digital media, storage device content, memory content, user and/or machine settings, and any other type of information existing in a digitized format, whether that format is binary or otherwise. The related term “back up”, as used herein, refers to the activity of producing a backup. The term “zero-touch back up”, as used herein, refers to a system, such as one based on the technologies described herein, creating a backup with minimal or no intervention from a user of a device being backed-up. The types of activities avoided in a zero-touch back up system typically include requiring the user to load tapes, floppy disks, compact disks (“CDs”), or the like, push buttons, run programs, etc. at the time of the backup. 
     The terms “point-in-time backup” and “point-in-time backup version”, as used herein, refer to backups made at a particular point in time, and that can be identified by a user based on the point in time the backup was made. Such a backup typically includes the data that was stored on a machine, or stored on one or more volumes of the machine, at the point in time the backup was made. For example, a user may be interested in restoring a file contained in a point-in-time backup created on Mar. 1, 2006 at 9:30 pm. 
     The verb “restore”, as used herein, refers to the act of restoring, reconstructing, re-creating, or the like, data from a backup to a storage device. The nouns “restore” and “recovery”, as used herein, refer to data being restored and/or the act of restoring data—for example, “doing a restore,” or “doing a recovery”. The storage device to which data is restored may be the device from which the data was originally backed up, or any other storage device. A restore may be “complete” or “partial”. For example, a user may replace a crashed hard drive, the only drive in their machine, and then restore the entire machine—a complete restore, or the user may restore a file, perhaps accidentally deleted, from a previous backup—a partial restore. 
     The term “bare-metal recovery” (“BMR”), as used herein, refers to a complete restore or recovery of a machine, typically the including operating system(s), user data, and user and machine settings as preserved in the backup being restored. A BMR may be performed on the machine from which the backup was originally made or, alternatively, on a different machine—such as when a user purchases a new PC to replace a current, older PC. 
     “Mounting” a storage device or a volume, as used herein, refers to making the volume accessible to a machine&#39;s file system such that data (files, folders, related metadata, and the like) on the mounted volume can be accessed by the machine. In one example, the present invention enables a backup created using the present examples to be mounted, as if the backup was a remote volume, thus enabling file system access by the machine to data in the backup. Further, such a mounting may be performed on a machine prior to the normal operating system being loaded, such as in a preinstallation environment such as the Microsoft Windows preinstallation environment (“WinPE”). 
     A file system typically includes a master file table (“MFT”) or the like that contains information about the files, folders and other data on a volume. Such information may be termed file system “metadata”—data about the files, folders, directories, and other data on the volume. This metadata typically includes “file records” or the like that describe files on the volume. A file record may also describe a folder, directory, or other data on the volume. A file record typically includes data about a file or folder such as time stamps, attributes, the file&#39;s or folder&#39;s name, security information, file or folder content or data, references or pointers to additional content or data not present in the file record, etc. Some types of file records may contain other data and/or may not include some of the example data listed here. Such a file record can typically be analyzed to determine if a file or the like has changed over time, or whether it has changed since the last time its file record was analyzed. 
     Examples of an MFT include a master file table as defined in the Microsoft Windows NT file system (“NTFS”), a file allocation table (“FAT”), and other tables or data structures for maintaining file system metadata. Examples of a file record include a file record as define in NTFS, a table or folder entry such as defined in a FAT, and other records, entries, data structures, and the like that describe files, folders, directories, and the like. The present invention may operate with these and/or other types of MFTs and file records. 
     File system data, metadata, files, folders, directories, and the like are typically stored on a storage device, such as a disk drive, in storage units known as “clusters”. Such a storage device is typically divided into clusters, the clusters being of uniform size, each cluster capable of holding a specific number of bytes of data. Thus, a cluster is typically the basic unit of storage for a storage device. Examples of cluster sizes include 2048 bytes, 4096 bytes, and 8192 bytes. When a file system stores information in a cluster, the cluster is said to be “in-use”. When the file system no longer needs the information previously stored in a cluster, such as when a file, a portion of which is stored in the cluster, is deleted or the like, the cluster may no longer be in-use, even if the data remains unchanged. The terms “cluster”, “cluster content”, and “cluster data” tend to be used interchangeably and generally refer to the data content of a cluster as the cluster. 
     The present invention makes use of hash values to uniquely identify the contents of clusters and other data structures, such as file records and the like. A hash value (“hash”), as used herein, is the output value of a function (“hash function” or “function”) that calculates a unique output value given some input data. Such a function is typically said to calculate a value that is “statistically unique” (“unique”) because the probability is very high that the function will produce different values given different input data, and will produce the same hash value given the same input data. Stated another way, a value is said to be “statistically unique” (“unique”) when it has a negligible probability of occurring again in a set of such values. One example of such a function is the message digest 5 (“MD5”) hashing function that calculates a fixed-size hash value from arbitrarily long input data. Other hashing function examples include the secure hash algorithm-1 (“SHA-1”) and the SHA-256 hashing functions. The present invention can operate using the foregoing example hashing functions or any other function or mechanism that calculates unique output values given different input data. In one example, the present invention calculates a file record hash by providing a file record to a hashing function as input data. In another example, a cluster hash is calculated by providing the content of a cluster as input data to a hashing function. 
       FIG. 2  is a block diagram showing example backup space requirements with and without single-instance storage across clients. Shown are two backup variations  210  and  260  and their respective backup storage requirements. Each circle represents the storage required for a client backup. Variation  210  does not use single-instance storage across clients while variation  260  does. Variation  210  shows the total backup storage space required for three clients when not making use of single-instance storage across client # 1 , client # 2 , and client # 3 . The total backup storage space required for variation  210  is the sum of the three circles. Variation  260  shows the total backup storage space required for the same three clients when making use of single-instance storage across the clients. The total backup storage space required for variation  260  is the sum of the three circles minus any data shared in common between the clients. Specifically, the backup storage space savings with variation  260  over variation  210  can be calculated as:
 
Backup storage space savings= D+E+F+G+G  
 
where, with respect to the above formula and as shown in variation  260  of  FIG. 2 :
 
     A=unique data on client # 1   
     B=unique data on client # 2   
     C=unique data on client # 3   
     D=data common to both client # 1  and client # 2   
     E=data common to both client # 2  and client # 3   
     F=data common to both client # 3  and client # 1   
     G=data common to all of client # 1 , client # 2 , and client # 3   
     In the case of multiple clients all being backed up by the same system, all of which include the same operating system and many of the same applications, programs, and other data, it can be seen that there will likely be much data in common between the clients. In a case such as this, significant backup storage space savings can be realized by making use of single-instance storage across clients. In one example of the present invention backing up 12 clients including 29 volumes, laboratory testing has shown that backup storage space savings of 80% or more are achievable over common backup techniques not making use of single-instance storage across clients. 
     The term “single-instance storage”, as used herein, refers to storing a single copy of data even when duplicates of the data exist multiple times. A reference to the single copy of the data is stored in the place of storing each duplicate copy of the data, as opposed to storing the duplicate data itself multiple times. The use of such a reference is typically made when the reference itself is smaller than the data it is replacing. The term “single-instance storage across clients”, as used herein, includes the meaning ascribed herein to single-instance storage and further includes using references for duplicate data when the duplicate data is found, not only on a single client, but also on multiple clients, all of which are being backed up by the same backup system. 
     Another aspect of the present invention for saving storage space is to exclude from client backups any temporary data, cached data, and the like, that exists on the client. Temporary and cache data typically includes: temporary files stored by Internet browsers, such as temporary Internet files, temporary index files, etc.; temporary files created when installing and/or deleting applications; temporary files created by the operating system and by programs and applications, and the like; cache files created by virtual memory systems, such as page files and swap files; cache files created when a machine goes into hibernation, and the like. Such temporary and cache files may have no useful purpose upon restore and are typically not required for the proper operation of a machine. As described in more detail below, the present invention provides for automatically excluding such temporary and cache files from backups, thus reducing backup storage space requirements. 
       FIG. 3  is a block diagram showing example backup system  300  including backup engine (“BE”)  312  and client backup module (“CBM”)  322  and client restore module (“CRM”)  324 , both modules coupled to BE  312  via backup protocol (“protocol”)  360 . Client  120  and backup server  110  host the elements of backup system  300 . Client  120  is shown as an example client and may be any type of device that would benefit from backups. Any number of clients may be coupled to backup server  110  via protocol  360 . Client  120  includes volume  326 , an example volume benefiting from backup. Backup server  110  includes volume  316  for storing backups, temporary data used in the creation of backups, etc. Volume  316  may also include other data, such as the operating system for backup server  100 , the BE  312  application, other applications and data, etc. 
     Example client backup module  322  and example client restore module  324  are shown in  FIG. 3  as separate software modules. In another example, CBM  322  and CRM  326  may be implemented as a single software module or, alternatively, as a collection of several modules together providing equivalent functionality. Such a software module may be implemented as an executable program, a device driver, script, application, or the like. 
     Backup protocol  360  provides a set of protocol messages (“messages”) for communications and exchange of information between clients, such as client  120 , and backup server  100 . Protocol  360  is typically used over a network. Protocol  360  is used by CBM  322  and CRM  326 , operating on example client  120 , to perform backup and restore operations in conjunction with BE  312 , operating on backup server  110 . In one example, as a matter of convention, messages sent by a client are termed “requests” while messages sent by a backup server are termed “responses.” In another example, the client and backup server may be the same device. 
     One portion of protocol  360  enables clients to discover the existence of backup servers so that a client can subsequently establish a backup protocol session with a backup server. Included in protocol  360  is a message the client can send to discover any backup servers that exist on the client&#39;s network, as well as a message for backup servers to respond to a client discovery request. Following is an example of such discovery messages. In the example, each message includes: a “name”, which is the name of the message; a “type”, which is either a “request” indicating the message is sent by a client, or a “response” indicating the message is sent by a backup server; a “description” that describes the purpose and function of the message; a “message code” that is an integer value that uniquely identifies the message within protocol  360 ; and a list of “parameters” indicating specific data accompanying the message, including the name and type of any parameters along with a description of the parameters. 
     In the example, user datagram protocol (“UDP”) over internet protocol (“IP”) via port number  8912  is used to transport protocol  360  discovery messages. In alternate examples, any port number and any connectionless transport protocol, such as Internetwork Packet Exchange (“IPX”) or the like, may be used as well as connection-oriented transport protocols such as Transmission Control Protocol (“TCP”), Sequenced Packet Exchange (“SPX”), Transport Layer Security (“TLS”), or the like. In yet another example, universal plug and play (“UPnP”) or the like may be used for backup server discovery. 
     Protocol  360  Example Discovery Message Set: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: DiscoverServers 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: A client broadcasts a DiscoverServers request in order to discover backup servers that exist on the network. The client expects to receive a ServerHere response from each backup server. 
             Message code: 0 
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ServerHere 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: Whenever a back server receives a DiscoverServers request, it responds to the sender with a ServerHere response. The response is sent to the IP address and port number from which the DiscoverServers request was received. 
             Message code: −1 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: serverName 
                 Type: string 
               
               
                   
                 Name: currentVersion 
                 Type: integer 
               
               
                   
                 Name: lowestVersion 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             serverName is a displayable name of the backup server, the short-form machine name. 
             currentVersion is the version of the TCP protocol that was current when the backup server was compiled. 
             lowestVersion is the lowest version of the TCP protocol that the backup server understands. 
           
         
       
    
     To discover a backup server, client  120  sends a DiscoverServers request. This request is typically broadcast—that is, sent to all devices networked to the client. Any backup server receiving this request typically sends a ServerHere response including a serverName parameter uniquely identifying the responding backup server. The parameters in the ServerHere response may be used by the client to establish a TCP connection and session with the backup server. With the establishment of the TCP session, a backup protocol session (“protocol session”) is also established and protocol  360  enters the AwaitingBanner state. This and other example protocol states are described below. Alternatively, a protocol session may be established using TLS over TCP, or any reliable session-oriented protocol. 
     In one example, protocol  360  defines a set of protocol states, each state describing what messages are legal for a client and/or backup server to send while the protocol is in a particular state. Sending or receiving some messages may change the state of protocol  360  while other messages may leave the protocol state unchanged. Each state includes: a “name” that identifies the state; a “description” that describes the state; a list of “allowed requests” indicating client requests allowed while the protocol is in the state; and a list of “allowed responses” indicating backup server responses allowed while the protocol is in the state. 
     Protocol  360  Example State Set: 
     
         
         
           
             Name: AwaitingBanner 
             Description: A newly opened TCP session puts the protocol in this state. 
             Allowed Requests: (none) 
             Allowed Responses: Banner 
             Name: AwaitingProtocolVersion 
             Description: A protocol session enters this state once in its lifetime, after a Banner response is sent. 
             Allowed Requests: ProtocolVersion 
             Allowed Responses: (none) 
             Name: Idle 
             Description: In this state, the protocol session has been fully established, but specific operation is occurring. The protocol returns to this state after any operation is completed. Absent catastrophic errors, the client should only close the TCP connection while in this state. The backup server should only close the TCP connection after the client has done so. 
             Allowed Requests: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 BeginBackupSet 
               
               
                   
                 GetMachines 
               
               
                   
                 GetVolumeConfigs 
               
               
                   
                 GetBackupSets 
               
               
                   
                 GetVolumes 
               
               
                   
                 BeginNtlmAuth 
               
               
                   
                 SimpleAuth 
               
               
                   
                 BeginRestore 
               
               
                   
                 SetBackupSchedule 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Allowed Responses: (none) 
             Name: AwaitingBeginBackupSetResponse 
             Description: In this state, a BeginBackupSet request has been sent, but the corresponding BeginBackupSet response has not. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Waiting 
               
               
                   
                 BeginBackupSet 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingBeginBackupResponse 
             Description: In this state, a BeginBackup request has been sent, but the corresponding BeginBackup response has not. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 BeginBackup 
               
               
                   
                 BeginBackupFailed 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingVolumeConfigRequest 
             Description: In this state, a BeginBackupSet response has been sent, but the corresponding EndVolumeConfig request has not. 
             Allowed Requests: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 VolumeConfig 
               
               
                   
                 EndVolumeConfig 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Allowed Responses: (none) 
             Name: AwaitingBeginBackupRequest 
             Description: In this state, a backup set has been started, but no individual volume backup operation is in progress. 
             Allowed Requests: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 BeginBackup 
               
               
                   
                 EndBackupSet 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Allowed Responses: (none) 
             Name: FileRecordHash 
             Description: In this state, the backup server is sending FileRecordHash responses describing the state of the previous backup operation, and the client is sending FileRecordHash requests describing the state of the current backup operation. 
             Allowed Requests:
           FileRecordHash   
         
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 FileRecordHash 
               
               
                   
                 EndFileRecordHash 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: EndFileRecordHash 
             Description: In this state, the backup server has sent an EndFileRecordHash response to the client, but the client has not yet sent an EndFileRecordHash request to the server. 
             Allowed Requests: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 FileRecordHash 
               
               
                   
                 EndFileRecordHash 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Allowed Responses: (none) 
             Name: AwaitingClusterHashCount 
             Description: In this state, the client has sent an EndFileRecordHash request, but has not yet sent a ClusterHashCount request. 
             Allowed Requests:
           ClusterHashCount   
         
             Allowed Responses: (none) 
             Name: ClusterHash 
             Description: In this state, the client is sending hashes of clusters to the backup server. 
             Allowed Requests: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 ClusterHash 
               
               
                   
                 ClusterUnchanged 
               
               
                   
                 EndClusterHashes 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Allowed Responses: (none) 
             Name: BackupWorking 
             Description: In this state, the client is waiting for the backup server to determine which clusters it needs. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Working 
               
               
                   
                 NeedClusterCount 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: BackupClusterData 
             Description: In this state, the backup server is sending NeedClusterData responses and the client is sending ClusterData requests. 
             Allowed Requests:
           ClusterData   
         
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 NeedClusterData 
               
               
                   
                 EndNeedClusterData 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingEndBackupRequest 
             Description: In this state, the backup server has sent an EndNeedClusterData response, but the client may not have finished sending ClusterData requests. 
             Allowed Requests: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 ClusterData 
               
               
                   
                 EndBackup 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Allowed Responses: (none) 
             Name: AwaitingEndBackupResponse 
             Description: In this state, the client has sent an EndBackup request, but the backup server has not yet sent an EndBackup response. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Working 
               
               
                   
                 EndBackup 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingEndBackupSetResponse 
             Description: In this state, the client has sent an EndBackupSet request, but the backup server has not yet sent an EndBackupSet response. 
             Allowed Requests: (none) 
             Allowed Responses:
           EndBackupSet   
         
             Name: AwaitingMachines 
             Description: In this state, the client has sent a GetMachines request, but the backup server has not yet sent an EndMachines response. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Machine 
               
               
                   
                 EndMachines 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingVolumeConfigs 
             Description: In this state, the client has sent a GetVolumeConfigs request, but the backup server has not yet sent an EndVolumeConfigs response. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 VolumeConfig 
               
               
                   
                 EndVolumeConfigs 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingBackupSets 
             Description: In this state, the client has sent a GetBackupSets request, but the backup server has not yet sent an EndBackupSets response. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 BackupSet 
               
               
                   
                 EndBackupSets 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingVolumes 
             Description: In this state, the client has sent a GetVolumes request, but the backup server has not yet sent an EndVolumes response. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Volume 
               
               
                   
                 EndVolumes 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingNtlmResponse 
             Description: In this state, the client has sent a BeginNtlmAuth or ContinueNtlmAuth request that the backup server has not yet responded to. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 ContinueNtlmAuth 
               
               
                   
                 Authorized 
               
               
                   
                 NotAuthorized 
               
               
                   
                 AuthFailed 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingNtlmRequest 
             Description: In this state, the backup server has sent a ContinueNtlmAuth response to which the client has not yet responded. 
             Allowed Requests:
           ContinueNtlmAuth   
         
             Allowed Responses: (none) 
             Name: AwaitingSimpleAuth 
             Description: In this state, the client has sent a SimpleAuth request to which the backup server has not yet responded. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Authorized 
               
               
                   
                 NotAuthorized 
               
               
                   
                 AuthFailed 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingBeginRestore 
             Description: In this state, the client has sent a BeginRestore request to which the backup server has not yet responded. 
             Allowed Requests: (none) 
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Waiting 
               
               
                   
                 Working 
               
               
                   
                 BeginRestore 
               
               
                   
                 BeginRestoreFailed 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: Restoring 
             Description: In this state, a restore operation is in progress. 
             Allowed Requests: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 GetClusters 
               
               
                   
                 EndRestore 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Allowed Responses: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 ClusterData 
               
               
                   
                 ClusterDataBad 
               
               
                   
                 ClusterDataMissing 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: AwaitingEndRestore 
             Description: In this state, the client has sent an EndRestore request to which the backup server has not yet responded. 
             Allowed Requests: (none) 
             Allowed Responses:
           EndRestore   
         
             Name: AwaitingSetBackupScheduleResponse 
             Description: In this state, the client has sent a SetBackupSchedule request to which the backup server has not yet responded. 
             Allowed Requests: (none) 
             Allowed Responses:
           SetBackupSchedule   
         
           
         
       
    
     Once a protocol session is established, protocol state transitions result from the client and server in the session sending various protocol messages (“messages”) to each other. One example of a set of protocol  360  request and response messages is provided below. In the example, each message includes: a “name”, which is the name of the message; a “type”, which is either a “request” indicating the message is for sent by a client, or a “response” indicating the message is sent by a backup server; a “description” that describes the purpose and function of the message; a “message code” that is an integer value that uniquely identifies the message within the protocol; a “prestate” that indicates allowed states prior to the message being sent; a “poststate” that indicates the new state of the protocol after the message is sent; and a list of “parameters” indicating specific data accompanying the message, including the name and type of any parameters and a description of the parameters. 
     In the example, Transmission Control Protocol (“TCP”), over Internet Protocol (“IP”) via port number  8912  is used to transport protocol  360  request and response messages. In alternate examples, any port number and any connection-oriented transport protocol, such as Sequenced Packet Exchange (“SPX”) or the like, may be used as well as connectionless transport protocols such as User Datagram Protocol (“UDP”), Internetwork Packet Exchange (“IPX”), or the like. 
     Protocol  360  Example Message Set: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: Abort 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: An Abort request is sent by the client to indicate that something catastrophic has occurred and the protocol session cannot continue. Unlike other messages, an Abort request may be sent at any time. After sending an Abort, the client should close the TCP connection. 
             Message code: 1 
             Prestate: any 
             Poststate: (none) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: reason 
                 Type: string 
               
               
                   
                   
               
            
           
         
       
         
         
           
             reason contains text describing the reason for the Abort request. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: Abort 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: An Abort response is sent by the backup server to indicate that something catastrophic has occurred and the session cannot continue. Unlike other messages, an Abort response may be sent at any time. After sending an Abort, the server should close the TCP connection 
             Message code: −1 
             Prestate: any 
             Poststate: any 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: reason 
                 Type: string 
               
               
                   
                   
               
            
           
         
       
         
         
           
             reason contains text describing the reason for the Abort request. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: Banner 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The Banner response is sent by the backup server immediately after the TCP connection is established. 
             Message code: −2 
             Prestate:
           AwaitingBanner   
         
             Poststate:
           AwaitingProtocolVersion   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: currentVersion 
                 Type: integer 
               
               
                   
                 Name: lowestVersion 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             currentVersion is the version of the protocol that was newest when the backup server code was built. 
             lowestVersion is the oldest version of the protocol that the backup server understands. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ProtocolVersion 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: This is the first message sent by the client; it chooses the version of the protocol that will be used. 
             Message code: 2 
             Prestate:
           AwaitingProtocolVersion   
         
             Poststate:
           Idle   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: versionNumber 
                 Type: integer 
               
               
                   
                 Name: lcid 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             versionNumber must be in the range of versions supported by the backup server as contained in the previous Banner response. 
             lcid is a locale id describing the client&#39;s preferred language (and similar parameters) for messages from the backup server. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: Waiting 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: A Waiting response is sent by the backup server when there will be a delay before the requested operation can be started, typically because some other operation is in progress. 
             Message code: −3 
             Prestate: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 AwaitingBeginBackupSet 
               
               
                   
                 AwaitingBeginRestore 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: count 
                 Type: integer 
               
               
                   
                 Name: machineName 
                 Type: string 
               
               
                   
                 Name: percentDone 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             count is the number of operations that are pending before the current one. 
             machineName occurs count times, and are the names of the machines that initiated the pending operations, in the order in which they will be performed. 
             percentDone is the estimated completion percent of the first pending operation, in the range [0 . . . 100] inclusive. 
             Name: Working Type: response 
             Description: The backup server sends this response while working on an operation that may take a while. 
             Message code: −4 
             Prestate: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 BackupWorking, 
               
               
                   
                 AwaitingBeginRestore 
               
               
                   
                 AwaitingEndBackupResponse 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: percentDone 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             percentDone is the estimated completion percent of the operation, in the range [0 . . . 100] inclusive. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginBackupSet 
                 Type: resquest 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends this message to begin a new backup set. 
             Message code: 3 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingBeginBackupSetResponse   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: computerGuid 
                 Type: byte[16] 
               
               
                   
                 Name: computerName 
                 Type: string 
               
               
                   
                 Name: computerDescription 
                 Type: string 
               
               
                   
                 Name: backupCount 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             computerGuid is a GUID chosen by the client machine. It should be unique across all different clients, but unchanging over time for a single client. 
             computerName is a name for the client machine. 
             computerDescription is a string description of the client machine. 
             backupCount is the number of volumes that the client expects to back up in this backup set. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginBackupSet 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: A client sends this message to begin a new backup set. 
             Message code: −5 
             Prestate:
           AwaitingBeginBackupSetResponse   
         
             Poststate:
           AwaitingVolumeConfigRequest   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: backupSetIndex 
                 Type: Integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             backupSetIndex is the index of the new backup set. The first backup set index for any client is 1, and the indices increment sequentially. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: VolumeConfig 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these messages for each volume whose configuration is to be remembered by the backup server. This may include volumes other than those being backed up. 
             Message code: 4 
             Prestate:
           AwaitingVolumeConfigRequest   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: uniqueIdentifier 
                 Type: byte[ ] 
               
               
                   
                 Name: friendlyName 
                 Type: string 
               
               
                   
                 Name: volumeBytes 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             uniqueIdentifier is a variable byte array unique identifier for the volume (from IOCTL_MOUNTDEV_GET_UNIQUE_ID). 
             friendlyName is a friendly name to associate with the volume (such as “C:”). 
             volumeBytes is the size of the volume, in bytes. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndVolumeConfig 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these messages after it has sent the last VolumeConfig request. 
             Message code: 5 
             Prestate:
           AwaitingVolumeConfigRequest   
         
             Poststate:
           AwaitingBeginBackupRequest   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginBackup 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: A client sends this message to begin a backup operation. 
             Message code: 6 
             Prestate: AwaitingBeginBackupRequest 
             Poststate: AwaitingBeginBackupResponse 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: uniqueIdentifier 
                 Type: byte[ ] 
               
               
                   
                 Name: volumeName 
                 Type: string 
               
               
                   
                 Name: fileSystem 
                 Type: string 
               
               
                   
                 Name: volumeSerialNumber 
                 Type: integer 
               
               
                   
                 Name: bytesPerSector 
                 Type: integer 
               
               
                   
                 Name: bytesPerCluster 
                 Type: integer 
               
               
                   
                 Name: initialVolumeBytes 
                 Type: integer 
               
               
                   
                 Name: isActive 
                 Type: boolean 
               
               
                   
                   
               
            
           
         
       
         
         
           
             uniqueIdentifier is a unique identifier for the volume (from IOCTL_MOUNTDEV_GET_UNIQUE_ID). 
             volumeName is the name or drive letter of the volume begin backed up. 
             fileSystem is the name of the file system used on the volume. For NTFS, this is the literal string “NTFS”. 
             volumeSerial is the serial number of the volume. 
             bytesPerSector is the number of bytes per sector on the volume&#39;s disk. 
             bytesPerCluster is the number of bytes per cluster on the volume&#39;s disk. 
             initialVolumeBytes is the size of the volume being backed up, in bytes. 
             isActive is true if the volume is the active partition on its disk. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginBackup 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends this response when it is willing to begin a backup operation. 
             Message code: −6 
             Prestate:
           AwaitingBeginBackupResponse   
         
             Poststate:
           FileRecordHash   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginBackupFailed 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends this response when it cannot initiate a backup operation for some reason. 
             Message code: −7 
             Prestate:
           AwaitingBeginBackupResponse   
         
             Poststate:
           Idle   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: reason 
                 Type: string 
               
               
                   
                   
               
            
           
         
       
         
         
           
             reason is a description of why the request failed. It is localized in the locale specified by the ProtocolVersion request. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: FileRecordHash 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests for each in-use file record on the volume. These are sent in strictly ascending order of file index. 
             Message code: 7 
             Prestate: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 FileRecordHash 
               
               
                   
                 EndFileRecordHash 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: fileIndex 
                 Type: integer 
               
               
                   
                 Name: hash 
                 Type: byte[16] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             fileIndex is the index of the file record. 
             hash is the MD5 hash of that file record. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: FileRecordHash 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these responses for each file record that was in use at the time of the last backup. These responses are typically sent in ascending order of file index. 
             Message code: −8 
             Prestate:
           FileRecordHash   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: fileIndex 
                 Type: integer 
               
               
                   
                 Name: hash 
                 Type: byte[16] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             fileIndex is the index of file record. 
             hash is the MD5 hash of the file record. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndFileRecordHash 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests after it has sent every FileRecordHash request, and it has received the EndFileRecordHash response. 
             Message code: 8 
             Prestate:
           EndFileRecordHash   
         
             Poststate:
           AwaitingClusterHashCount   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndFileRecordHash 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these requests after it has sent every FileRecordHash response. 
             Message code: −9 
             Prestate:
           FileRecordHash   
         
             Poststate:
           EndFileRecordHash   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ClusterHashCount 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests to inform the backup server of the maximum number of ClusterHash requests that it intends to send. The content of this request must be greater than or equal to the number of ClusterHash requests. 
             Message code: 9 
             Prestate:
           AwaitingClusterHashCount   
         
             Poststate:
           ClusterHash   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: count 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             count is an upper bound on the number of ClusterHash requests. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ClusterHash 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests for each cluster that is in use, if the client can&#39;t prove that the cluster is unchanged since the previous backup. Along with the ClustersUnchanged requests, these requests are sent in strictly ascending order of cluster index. 
             Message code: 10 
             Prestate:
           ClusterHash   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: clusterIndex 
                 Type: integer 
               
               
                   
                 Name: hash 
                 Type: byte[16] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             clusterIndex is the zero-based index of a cluster on the disk. 
             hash is the MD5 hash of the contents of that cluster. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ClustersUnchanged 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests for each contiguous run of clusters that are in use, for which the client can prove they haven&#39;t been changed since the previous backup. Along with the ClusterHash requests, these requests are sent in strictly ascending order of cluster index. 
             Message code: 11 
             Prestate:
           ClusterHash   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: clusterIndex 
                 Type: integer 
               
               
                   
                 Name: clusterCount 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             clusterIndex is the zero-based index of the first cluster of a run of clusters that are in use and unchanged. 
             clusterCount is the number of clusters in the run of clusters that are in use and unchanged. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndClusterHashes 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends this request after it has sent all of its ClusterHash and ClustersUnchanged requests. 
             Message code: 12 
             Prestate:
           ClusterHash   
         
             Poststate:
           BackupWorking   
         
             Parameters: (none) 
             Name: NeededClusterCount Type: response 
             Description: The backup server sends one of these requests to the client to inform it of an upper bound on the total number of clusters that will be requested via NeedClusterData responses. 
             Message code: −10 
             Prestate:
           BackupWorking   
         
             Poststate:
           BackupClusterData   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: maxClusterCount 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             maxClusterCount is a close upper bound on the number of clusters that will be requested via NeedClusterData responses. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: NeedClusterData 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these requests for each contiguous run of clusters that it wants the client to send the contents of. These will typically be in strictly ascending order of cluster index. 
             Message code: −11 
             Prestate:
           BackupClusterData   
         
             Poststate:
           BackupClusterData   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: clusterIndex 
                 Type: integer 
               
               
                   
                 Name: clusterCount 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             clusterIndex is the zero-based index of the first cluster of a contiguous run that should be sent to the backup server. 
             clusterCount is the number of clusters in the run that should be sent to the backup server. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ClusterData 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests for each cluster that the backup server needs the contents of. They are typically sent in increasing order of cluster index. 
             Message code: 13 
             Prestate: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 BackupClusterData 
               
               
                   
                 AwaitingEndBackupRequest 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: clusterIndex 
                 Type: integer 
               
               
                   
                 Name: clusterData 
                 Type: byte[ ] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             clusterIndex is the zero-based index of the cluster. 
             clusterData is a byte array of the contents of the cluster. Its length is typically the same as the clusterSize parameter of the BeginBackup request. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndNeedClusterData 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these responses after it has sent all of its NeedClusterData responses. 
             Message code: −12 
             Prestate:
           BackupClusterData   
         
             Poststate:
           AwaitingEndBackupRequest   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndBackup 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests to end the backup operation, to ask the backup server to commit the operation. 
             Message code: 14 
             Prestate:
           AwaitingEndBackupRequest   
         
             Poststate:
           AwaitingEndBackupResponse   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: minimumRestoreBytes 
                 Type: integer 
               
               
                   
                 Name: clientInfo 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             minimumRestoreBytes is the size of the smallest volume (in bytes) to which the backed-up image can be successfully restored. 
             clientInfo is any binary string. The back server will save, but typically not interpret, this string. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndBackup 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these responses upon successfully committing the backup. 
             Message code: −13 
             Prestate:
           AwaitingEndBackupResponse   
         
             Poststate:
           AwaitingBeginBackupRequest   
         
             Parameters: (none) 
             Name: EndBackupSet Type: request 
             Description: The client sends one of these requests after the last backup in a backup set has been completed. 
             Message code: 15 
             Prestate:
           AwaitingBeginBackupRequest   
         
             Poststate:
           AwaitingEndBackupSetResponse   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndBackupSet 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these messages in response to an EndBackupSet request. 
             Message code: −14 
             Prestate:
           AwaitingEndBackupSetResponse   
         
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: GetMachines 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: A client sends one of these requests to find out what client machines have backups in the backup server database. In response, the backup server will send a sequence of Machine responses followed by an EndMachines response. 
             Message code: 16 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingMachines   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: Machine 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: In response to a GetMachines request, the backup server sends one of these responses for each client machine in the database. 
             Message code: −15 
             Prestate:
           AwaitingMachines   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                 Name: machineName 
                 Type: string 
               
               
                   
                 Name: machineDescription 
                 Type: string 
               
               
                   
                 Name: scheduleDays 
                 Type: integer 
               
               
                   
                 Name: scheduleMinutes 
                 Type: integer 
               
               
                   
                 Name: macAddress 
                 Type: binary[6] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid, machineName, machineDescription, scheduleDays and scheduleMinutes are the values supplied by the most recent BeginBackupSet or SetBackupSchedule request from the client. 
             macAddress is the MAC address from which the most recent BeginBackupSet or SetSchedule request for the client was received. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndMachines 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these responses after sending all of its Machine responses. 
             Message code: −16 
             Prestate:
           AwaitingMachines   
         
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: GetVolumeConfigs 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests to find out what VolumeConfig information exists for a machine. In response, the backup server will send a sequence of volumeConfig responses followed by an EndVolumeConfigs response. 
             Message code: 17 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingVolumeConfigs   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid is the GUID of the client whose data is desired. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: VolumeConfig 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: In response to a GetVolumeConfigs request, the backup server sends one of these messages for each volume for which it has configuration data. 
             Message code: −17 
             Prestate:
           AwaitingVolumeConfigs   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                 Name: uniqueidentifier 
                 Type: byte[ ] 
               
               
                   
                 Name: friendlyName 
                 Type: string 
               
               
                   
                 Name: volumeSize 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid is the GUID of the client whose data is returned. 
             uniqueIdentifier, friendlyName and volumeSize are values from a previous VolumeConfig request. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndVolumeConfigs 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these messages after the last VolumeConfig response to a GetVolumeConfigs request. 
           
         
       
    
     Message code: −18
         Prestate:
           AwaitingVolumeConfigs   
           Poststate:
           Idle   
           Parameters: (none)       

     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: GetBackupSets 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these messages to determine what backup sets exist for a machine. In response, the backup server will send a sequence of BackupSet responses followed by an EndBackupSets response. 
             Message code: 18 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingBackupSets   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid is the identifier of the client whose data is desired. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BackupSet 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: In response to a GetBackupSets request, the backup server sends one of these messages for each backup set in the database. 
             Message code: −19 
             Prestate:
           AwaitingBackupSets   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                 Name: index 
                 Type: integer 
               
               
                   
                 Name: timestamp 
                 Type: integer 
               
               
                   
                 Name: authNeeded 
                 Type: boolean 
               
               
                   
                 Name: isComplete 
                 Type: boolean 
               
               
                   
                 Name: isDaily 
                 Type: boolean 
               
               
                   
                 Name: isWeekly 
                 Type: boolean 
               
               
                   
                 Name: isMonthly 
                 Type: boolean 
               
               
                   
                 Name: isYearly 
                 Type: boolean 
               
               
                   
                 Name: volumeCount 
                 Type: integer 
               
               
                   
                 Name: friendlyName 
                 Type: string 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid is the GUID of the client whose data is returned. 
             index is the 1-based index of the backup set described by this message. 
             timestamp is the time at which the backup was started, in FileTime format (number of decimicroseconds since 1 Jan. 1601, 0000 UTC). 
             authNeeded is true if the client will need to authenticate himself as a backup server administrator before being allowed to do a restore. 
             isComplete is true if this backup set was completed (via EndBackupSet request and response). 
             isDaily is true if this is the machine&#39;s first backup set of the day. 
             isWeekly is true if this is the machine&#39;s first backup set of the week. 
             isMonthly is true if this is the machine&#39;s first backup set of the month. 
             isYearly is true if this is the machine&#39;s first backup set of the year. 
             volumeCount is the number of volumes contained in the backup set. 
             friendlyName is the friendly name of one of the volumes in the backup set. 
             This field occurs exactly volumeCount times. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndBackupSets 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these messages after the last BackupSet response to a GetBackupSets request. 
             Message code: −20 
             Prestate:
           AwaitingBackupSets   
         
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: GetVolumes 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends one of these requests to find out what volumes exist in the database for a particular client machine. In response, the backup server will send a sequence of Volume responses followed by an EndVolumes response. 
             Message code: 19 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingVolumes   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                 Name: backupSetIndex 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid is the GUID of the client whose data is desired. 
             backupSetIndex is the index of the backup set whose data is desired. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: Volume 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: In response to a GetVolumes request, the backup server sends one of these responses for each volume associated with a particular machine. 
             Message code: −21 
             Prestate:
           AwaitingVolumes   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                 Name: backupSetIndex 
                 Type: integer 
               
               
                   
                 Name: uniqueIdentifier 
                 Type: byte[ ] 
               
               
                   
                 Name: friendlyName 
                 Type: string 
               
               
                   
                 Name: fileSystem 
                 Type: string 
               
               
                   
                 Name: volumeSerial 
                 Type: integer 
               
               
                   
                 Name: bytesPerSector 
                 Type: integer 
               
               
                   
                 Name: bytesPerCluster 
                 Type: integer 
               
               
                   
                 Name: initialVolumeBytes 
                 Type: integer 
               
               
                   
                 Name: minimumRestoreBytes 
                 Type: integer 
               
               
                   
                 Name: usedClusterCount 
                 Type: integer 
               
               
                   
                 Name: isActive 
                 Type: boolean 
               
               
                   
                 Name: clientInfo 
                 Type: byte[ ] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid is the GUID of the client whose data is returned. 
             backupSetIndex is the index of the backup set whose data is returned. 
             uniqueIdentifier, friendlyName, fileSystem, volumeSerial, bytesPerSector, bytesPerCluster and isActive are the values from the associated BeginBackup request. 
             minimumRestoreBytes and clientInfo are the values from the associated EndBackup request. 
             usedClusterCount is a count of the number of clusters stored in the backed-up volume image. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndVolumes 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends one of these responses after sending its last Volume response. 
             Message code: −22 
             Prestate:
           AwaitingVolumes   
         
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginNtlmAuth 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends this request to begin an NTLM authentication. After some number of ContinueNtlmAuth responses and requests, the backup server will respond with Authorized, NotAuthorized or AuthFailed. 
             Message code: 20 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingNtlmResponse   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: authData 
                 Type: byte[ ] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             authData is the data returned by InitializeSecurityContext, a function for establishing a security context between two devices, or the like. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ContinueNtlmAuth 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends this request after receiving a ContinueNtlmAuth response. 
             Message code: 21 
             Prestate:
           AwaitingNtlmRequest   
         
             Poststate:
           AwaitingNtlmResponse   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: authData 
                 Type: byte[ ] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             authData is the data returned by InitializeSecurityContext or the like. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ContinueNtlmAuth 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends this response to either a BeginNtlmAuth or a ContinueNtlmAuth request, when more interactions are needed to complete the authentication. 
             Message code: −23 
             Prestate:
           AwaitingNtlmResponse   
         
             Poststate:
           AwaitingNtlmRequest   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: authData 
                 Type: byte[ ] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             authData is the data returned by AcceptSecurityContext 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: SimpleAuth 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends this request to perform a simple (plain-text) authentication. The backup server will send an Authorized, NotAuthorized or AuthFailed response. 
             Message code: 22 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingSimpleAuth   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: userName 
                 Type: string 
               
               
                   
                 Name: password 
                 Type: string 
               
               
                   
                 Name: domainName 
                 Type: string 
               
               
                   
                 Name: Authorized 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends this response to indicate that authentication was successful, and the supplied credentials are sufficient to authorize a restore operation. 
             Message code: −24 
             Prestate: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 AwaitingNtlmResponse 
               
               
                   
                 AwaitingSimpleAuth 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: NotAuthorized 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends this response to indicate that authentication was successful, but the supplied credentials are insufficient to authorize a restore operation. 
             Message code: −25 
             Prestate: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 AwaitingNtlmResponse, 
               
               
                   
                 AwaitingSimpleAuth 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: AuthFailed 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends this response to indicate that authentication was unsuccessful, typically usually because the user name or password was incorrect. 
             Message code: −26 
             Prestate: 
           
         
       
    
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 AwaitingNtlmResponse 
               
               
                   
                 AwaitingSimpleAuth 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginRestore 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends this request to start a restore operation. In response, the backup server will send zero or more Waiting responses followed by zero or more Working responses, followed by either a BeginRestore or a BeginRestoreFailed response. 
             Message code: 23 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingBeginRestore   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                 Name: backupSetIndex 
                 Type: integer 
               
               
                   
                 Name: uniqueIdentifier 
                 Type: byte[ ] 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid is the GUID of the machine whose data is to be restored. 
             backupSetIndex is the index of the backup set whose data is to be restored. 
             uniqueIdentifier is the unique identifier of the volume whose data is to be restored. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginRestore 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends this response upon successful preparation for a restore operation. 
             Message code: −27 
             Prestate:
           AwaitingBeginRestore   
         
             Poststate:
           Restoring   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: BeginRestoreFailed 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends this response when an attempt to begin a restore operation has failed. 
             Message code: −28 
             Prestate:
           AwaitingBeginRestore   
         
             Poststate:
           Idle   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: reason 
                 Type: string 
               
               
                   
                   
               
            
           
         
       
         
         
           
             reason is a description of why the request failed. It is localized in the locale specified by the ProtocolVersion request. 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: GetClusters 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends this request to ask the backup server to send the contents of a range of clusters. The backup server will respond with a series of ClusterData, ClusterDataBad and/or ClusterDataMissing responses that cover the requested range, in strictly increasing order. Note that the client may send a second GetClusters request before the first one has been satisfied. The backup server will typically respond with all of the data for the first request, then all of the data for the second one. 
             Message code: 24 
             Prestate:
           Restoring   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: firstClusterIndex 
                 Type: integer 
               
               
                   
                 Name: clusterCount 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: ClusterData 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends a ClusterData response to send the contents of a single cluster to the client, in response to a GetClusters request. 
             Message code: −29 
             Prestate:
           Restoring   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: clusterIndex 
                 Type: integer 
               
               
                   
                 Name: clusterData 
                 Type: byte[ ] 
               
               
                   
                 Name: ClusterDataBad 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends a ClusterDataBad response to the client to indicate that the contents of a range of clusters is unavailable, typically because of I/O errors or other failures. The specified range will be a subrange of that in the GetClusters request. 
             Message code: −30 
             Prestate:
           Restoring   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: clusterIndex 
                 Type: integer 
               
               
                   
                 Name: clusterCount 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Name: ClusterDataMissing Type: response 
             Description: The backup server sends a ClusterDataMissing response to the client to indicate that the contents of a range of clusters was not included in the backup image (because, for example, the clusters were not in use by any file). The specified range will be a subrange of that in the GetClusters request. 
             Message code: −31 
             Prestate:
           Restoring   
         
             Poststate: (unchanged) 
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: clusterIndex 
                 Type: integer 
               
               
                   
                 Name: clusterCount 
                 Type: integer 
               
               
                   
                 Name: EndRestore 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends an EndRestore request when it has successfully finished a restore operation. 
             Message code: 25 
             Prestate:
           Restoring   
         
             Poststate:
           AwaitingEndRestore   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: EndRestore 
                 Type: response 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The backup server sends an EndRestore response to reply to an EndRestore request. 
             Message code: −32 
             Prestate:
           AwaitingEndRestore   
         
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: SetBackupSchedule 
                 Type: request 
               
               
                   
                   
               
            
           
         
       
         
         
           
             Description: The client sends a SetBackupSchedule request to inform the backup server of the expected schedule for backup operations. 
             Message code: 26 
             Prestate:
           Idle   
         
             Poststate:
           AwaitingSetBackupScheduleResponse   
         
             Parameters: 
           
         
       
    
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Name: machineGuid 
                 Type: byte[16] 
               
               
                   
                 Name: machineName 
                 Type: string 
               
               
                   
                 Name: machineDescription 
                 Type: string 
               
               
                   
                 Name: scheduleDays 
                 Type: integer 
               
               
                   
                 Name: scheduleMinutes 
                 Type: integer 
               
               
                   
                   
               
            
           
         
       
         
         
           
             machineGuid is the client-chosen GUID for the current machine. 
             machineName is a name for the current machine. 
             machineDescription is a description string for the current machine. 
             scheduleDays is an integer bit-mapped field describing on which days backup is scheduled to run, as follows:
           1—Sunday   2—Monday   4—Tuesday   8—Wednesday   16—Thursday   32—Friday   64—Saturday   
         
             scheduleMinutes is the number of minutes after midnight, local time, that backup is scheduled to run. 
             Name: SetBackupSchedule Type: response 
             Description: The backup server sends a SetBackupSchedule response to reply to a SetBackupSchedule request. 
             Message code: −33 
             Prestate:
           AwaitingSetBackupScheduleResponse   
         
             Poststate:
           Idle   
         
             Parameters: (none) 
           
         
       
    
     In one example, the various data types used by protocol messages are structured and transmitted as follows: 
     Integers—An integer is transmitted using a variable number of bytes; the smallest possible integer is sent as one byte while the largest possible 64-bit integer is sent as 10 bytes. The least significant 7 bits of the value are sent in the first byte; the most significant 0×80 bit is set if more bytes are to follow. If the integer&#39;s value is in the range [−64 . . . +63], then the integer comprises only one byte. Otherwise, the 0×80 bit is set in the first byte. Subsequent bytes each encode successive 7 bits of the value. In each byte except the last one, the 0×80 bit is set. In the last byte, the 0×40 bit is treated as a sign bit; this bit is repeated as necessary to fill out the length of the integer. 
     Booleans—A boolean false is transmitted as a single byte with value 0; a boolean true is transmitted as a single byte with value 1. (Note that this is the same encoding as an Integer 0 or 1.) 
     Fixed-length byte arrays—A fixed-length byte array is transmitted as the bytes of the array, with the lowest-indexed byte first. Since it&#39;s a fixed-length array, the receiver (by definition) knows how many bytes to expect. A fixed-length byte array containing, for example, 16 bytes is indicated herein by “byte[16]”. MD5 hashes, for example, tend to be 16 bytes long and transmitted as fixed-length byte arrays. 
     Variable-length byte arrays—A variable-length byte array is transmitted by sending the byte count, encoded as an integer as described above, followed by the contents of the array, lowest index first. A variable-length byte array is indicated herein by “byte [ ]”. 
     String—a string is transmitted as an integer containing the count of characters in the string followed by the characters of the string. In one example, the count and string characters are represented as bytes in universal character set transformation format 8 (“UTF-8”). 
     Message—Each message has a unique message code, which is transmitted first, encoded as an integer as described above. This is followed by the fields of the message; the types of these fields depend on the specific message. 
       FIG. 4  is a block diagram showing example protocol state transitions and messages for backup protocol session establishment and abort operations. The state transitions and message are based on the example protocol state and message sets described above. To establish a protocol session between a client and a backup server, the client sends the DiscoverServers request and receives a ServerHere reply from a backup server, as described above. Given the ServerHere reply, the client establishes a TCP connection with the backup server via example port number  8912 . At this point the client and server have established a backup protocol session. 
     Once a client establishes a TCP session and backup protocol session  410  with a backup server, the protocol enters AwaitingBanner state  420 . Once in AwaitingBanner state  420 , the backup server sends a Banner response message  430  to the client including a currentVersion parameter indicating the latest version of the protocol that the backup server understands, and a lowestVersion parameter indicating the oldest version of the protocol the backup server understands. After sending Banner response  430 , the protocol enters AwaitingProtocolVersion state  440 . 
     In response to Banner response  430  sent by the backup server, the client sends a ProtocolVersion request  450  to the backup server to indicate the version of the protocol to be used for the protocol session, which is typically in the range indicated by the currentVersion and lowestVersion parameters provided by Banner response  430 . At this point the protocol transitions to Idle state  460  and is ready for normal operation. 
     At any state during a protocol session, as indicated by block  470 , the client may send an Abort request  482  to the backup server indicating that a failure has occurred such that the client cannot continue the protocol session. The client typically closes the backup protocol TCP session on its end after sending an Abort request  482 , and the backup protocol session between the client and backup server is terminated as indicated by block  490 . The backup server typically closes the backup protocol TCP session on its end upon receipt of an Abort request  482 . 
     Similarly, should the backup server experience a failure such that it cannot continue the protocol session, it may send an Abort response  484  to the client during any protocol state, as indicated by block  470 . The backup server typically closes the backup protocol TCP session on its end after sending an Abort response  484 , and the backup protocol session between the client and backup server is terminated as indicated by block  490 . The client typically closes the backup protocol TCP session on its end upon receipt of an Abort response  484 . 
       FIG. 5  is a block diagram showing a simplified example backup process for performing a cluster-based backup. The process begins at block  520  by comparing the state of a file system to be backed up to a previously stored state of the same file system, if any. A previous state of the file system is typically stored by the backup system as a part of any previous backup operation. Typically the file system is that of a single volume or a set of volumes. The state of the file system includes data and metadata in the file system such as cluster contents, file records, files, folders, and any other file system data. Comparing the states determines if anything has changed in the file system relative to the file system&#39;s previous state, such as a file being modified, added, deleted, a folder being added, a file or folder timestamp, such as the last modified date, being changed, or the like. If there is no previous state available, then the entire file system is considered to have changed since it was not previously known. Such a backup, with no previous state available, is known as a “complete” backup indicating that the file system is completely backed up. Alternatively, when some of the file system data is already backed up by the backup system, then an “incremental” backup is performed. 
     In one example, the file system is linearly scanned, hashing each file record and checking for changes relative to the previous state. The set of current file record hashes generated is provided to the backup system for future use. The file record hashes may be generated using a hashing function, such as an MD5 hashing function. 
     At block  530 , if no changes to the file system are detected, then the backup process is complete as there is nothing new to backup since the previous file system state was backed up. If, on the other hand, there is some difference between the current and previous file system states, then the process continues at block  540 . In one example this check may not occur as it tends to be unlikely in modern file systems to not have changes, even over a very brief period of time. 
     At block  540 , the specific clusters that have changed, or that may have changed, are determined. In one example, this is done by noting that a file record has changed as part of comparing the current and previous file system states. Given a changed file record, the clusters associated with the changed file record are determined. One or more of the associated clusters may have changed since the previous backup as indicated by the changed file record which indicates that there has been some change to the file, folder, or other data represented by the file record. 
     Volume clusters may be categorized into one of three categories. 1) “Uninteresting clusters”: these are clusters that are currently not allocated for use by the file system or clusters associated with ephemeral files that typically need not be included in a backup. 2) “Unchanged clusters”: these are clusters that are not in the first category, and associated with files for which the file system metadata indicates that file contents have not changed. 3) “Potentially changed clusters”: these are clusters that are in neither the first nor second category; they represent clusters that may have changed since the previous backup. 
     At block  550 , a “current cluster hash” is generated for each cluster in the file system that may have changed—the potentially changed clusters. In one example, this is done by using a hashing function, such as an MD5 hashing function. In another example, the current cluster hashes and a list of unchanged clusters provided to the backup system. The backup system compares each current cluster hash to the corresponding cluster hash of the previous backup, if any, and creates a set of cluster and hash pairs for which the cluster contents have changed since the previous backup and sorts the set into hash order. 
     At block  560 , the current cluster hashes are compared to cluster hashes already stored by the backup system. There is typically one such stored cluster hash for each cluster backed up by the backup system. For example, if the backup system includes backups of 10 different clients, then the current cluster hashes are compared again the stored cluster hashes of all 10 different clients. If a match is found, that is, a current cluster hash is the same as a stored cluster hash, then the content for the current cluster hash is not needed as it is already stored by the backup system. Any current cluster hash for which there is not a matching stored cluster hash represents a cluster&#39;s content that is not currently stored by the backup system, and is therefore considered needed. 
     At block  570 , the needed cluster contents are retrieved from the file system being backed up and stored by the backup system. Once all needed cluster content has been retrieved and stored, the entire backup is committed, as indicated by block  580 , and the process is complete. An example commit process is described in connection with  FIG. 16 . 
       FIG. 6  is a block diagram showing example protocol state transitions and messages for performing a cluster-based backup operation during a protocol session. The state transitions are based on the example protocol states and messages described above. Starting at Idle state  460 , the client in the protocol session sends a BeginBackupSet request  602  to the backup server including a computerGuid parameter uniquely identifying the client. The protocol then enters AwaitingBeginBackupResponse state  620 . The backup server may send one or more Waiting responses  613  to the client if there will be a delay in performing the requested operation. When the backup server is able to begin a new backup set for the client, it sends a BeginBackupSet response  615  to the client and the protocol transitions to AwaitingVolumeConfigRequest state  620 . A backup set is typically a backup of one or more volumes. 
     Upon client receipt of BeginBackupSet response  615 , the client sends zero or more VolumeConfig requests  622  to the backup server, each request including a uniqueIdentifier parameter that uniquely identifies a volume that the backup server is to maintain information about. After the client has identified zero or more volumes to the backup server, it sends an EndVolumeConfig request  624  to the backup server and the protocol transitions to AwaitingBeginBackupRequest state  630  indicating that a backup set has begun, but no individual volume backup operation is currently in progress. This state may also be entered via an EndBackup response  695  as indicated in  FIGS. 6 and 7  by block  693 . 
     While the protocol is in AwaitingBeginBackupSet state  630 , the client may send an EndBackupSet request  632  indicating that the last volume backup in a backup set of zero or more backups has been completed, resulting in transitioning the protocol state to AwaitingEndBackupSetResponse state  680 . In response to the EndBackupSet request  632  from the client, the server sends an EndBackupSet response  683  to the client and the protocol transitions back to Idle state  460 . Alternatively, while the protocol is in AwaitingBeginBackupSet state  630 , the client may send a BeginBackup request  634  to the backup server, the request  634  including a uniqueIdentifier parameter that uniquely identifies the client volume to be backed up. Reception of the BeginBackup request  634  by the backup server transitions the protocol to AwaitingBeginBackupResponse state  640 . 
     In the event that the backup server is unable to initiate a backup operation responsive to BeginBackup request  634 , it sends a BeginBackupFailed response  645  to the client. Response  645  includes a reason parameter that identifies the reason for the failure. Following the sending of a BeginBackupFailed response  645 , the protocol returns to Idle state  460 . Alternatively, if and when the backup server is able to begin the backup operation, it sends a BeginBackup response  643  to the client and the protocol transitions to FileRecordHash state  650 . 
     While the protocol is in FileRecordHash state  650 , the backup server sends one FileRecordHash response  653  to the client including a hash of each file record previously provided to the backup server by the client at the time of the last backup, if any. These files record hashes may be used by the client to determine what files on the client may have changed since the last backup. Once all such file record hashes have been sent to the client, the backup server sends an EndFileRecordHash response  655  and the protocol transitions to. 
     While the protocol is in either FileRecordHash state  650  or EndFileRecordHash state  660 , the client scans the volume to be backed up and computes hashes for each file record, compares these current file records hashes to those sent by the backup server via FileRecordHash responses  653  to determine which may have changed since the last backup, and sends each changed file record hash to the backup server using a FileRecordHash request  652 . Once all of the changed file record hashes are sent by the client, and the protocol has transitioned to EndFileRecordHash state  660 , the client sends an EndFileRecordHash request  664  and the protocol transitions to AwaitingClusterHashCount state  670 . 
     Once the protocol is in AwaitingClusterHashCount state  670 , the client sends a ClusterHashCount request  672  indicating the maximum number of ClusterHash requests ( FIG. 7   a ,  712 ) that will be sent. At this point the protocol transitions to ClusterHash state  710 , as shown in  FIG. 7   a  via figure transition indicator  692 . 
       FIG. 7   a  is a block diagram showing a continuation of example protocol state transitions and messages for performing a cluster-based backup operation. While the protocol is in ClusterHash state  710 , the client sends a cluster hash to the backup server via a ClusterHash request  712  for each in-use cluster on the volume that has changed since the last backup. The client also sends zero or more ClustersUnchanged requests  714  to the backup server, each request  714  identifying a contiguous run of in-use clusters that have not changed since the last backup. Once the client has sent all the ClusterHash requests  712  and ClustersUnchanged requests  714 , it sends an EndClusterHashes request  716  to the backup server and the protocol transitions to BackupWorking state  720 . 
     While the protocol is in BackupWorking state  720 , the backup server may send one or more working responses  723 , indicating that it is currently busy working on an operation. When not busy while in BackupWorking state  720 , the backup server sends a NeedClusterCount response  725  to the client indicating an upper bound on the total number of clusters for which contents will be requested via NeedClusterData responses  733 . Once the NeedClusterCount response  725  has been sent to the client, the protocol transitions to BackupClusterData state  730 . 
     While the protocol is in BackupClusterData state  730 , the backup server sends zero of more NeedClusterData responses  733  for the clusters contents required for backup. In one example, one request  733  is sent for each contiguous range of clusters for which the content is needed for backup. Once all NeedClusterData responses  733  have been sent to the client, the backup server sends an EndNeedClusterData response  735  to the client and the protocol transitions to AwaitingEndBackupRequest state  740 . 
     While the protocol is in either BackupClusterData state  730  or AwaitingEndBackupRequest state  740 , the client sends cluster contents to the backup server via ClusterData requests  732 . Once all ClusterData requests  732  have been sent to the backup server, and the protocol has transitioned to AwaitingEndBackupRequest state  740 , the client sends an EndBackup request  744  to the backup server, requesting the backup server to commit the backup operation, and the protocol transitions to AwaitingEndBackupResponse state  750 . An example commit process is described in connection with  FIG. 16 . 
     While the protocol is in AwaitingEndBackupResponse state  750  the backup server commits the backup operation and may send a working response to the client indicating that it is busy with an operation such as the commit. When not busy, the backup server sends an EndBackup response  695  to the client and the protocol transitions to AwaitingBeginBackup state  630  as shown in  FIG. 6  and the backup operations continue as described above for state  630  where the backup set is ended or another volume in the backup set is backed up. 
       FIG. 7   b  is a block diagram showing example protocol state transitions and messages for discovering client machines that have one or more backups in a backup server&#39;s database (“backup database” or “database”). A backup server may backup multiple clients and thus contain backups for each of those multiple clients in its backup database. The state transitions, client requests and backup server responses shown in  FIG. 7   b  provide one example of how to discover what client machines have backup in a backup database using the protocol states and messages detailed above. 
     The machine discovery process may begin when the protocol is in Idle state  460 . At this point, a client may send a GetMachines request  762  to the backup server, upon receipt of which the protocol transitions to AwaitingMachines state  760 . While the protocol is in state  760 , the backup server sends zero or more Machine responses  763 , each response including a machineGuid parameter that uniquely identifies a machine with a backup in the backup database. Once all of the Machine responses  763  are sent to the client, the backup server sends an EndMachines response  765  to the client and the protocol transitions back to Idle state  460 . 
       FIG. 8   a  is a block diagram showing example protocol state transitions and messages for discovering any backup sets for a particular machine that are stored in a backup server&#39;s database. A backup database may include multiple backup sets for a particular machine, each backup set having been created at a different point in time. For example, a backup database may include two backup sets for machine A: the first having been created on January 10 th  starting at 9:30 pm and the second having been created on February 10 th  starting at 11:00 pm. 
     The backup set discovery process may begin when the protocol is in Idle state  460 . At this point, a client may send a GetBackupSets request  812  to the backup server, the request including a machineGuid parameter that uniquely identifies a machine. Upon receipt of the GetBackupSets request  812  by the backup server the protocol transitions to AwaitingBackupSets state  810 . While the protocol is in state  810 , the backup server sends zero or more BackupSet responses  813 , each response including a friendlyName parameter that uniquely identifies a backup set for the machine. Once all of the BackupSet responses  813  are sent to the client, the backup server sends an EndBackupSets response  815  to the client and the protocol transitions back to Idle state  460 . 
       FIG. 8   b  is a block diagram showing example protocol state transitions and messages for discovering any volume configurations for a particular machine that are stored in a backup server&#39;s database. A volume configuration is a description of a volume associated with a specific client machine. A backup database may include multiple volume configurations for a particular machine. For example, a backup database may include two volume configurations machine A: the first having been created for a 200 GB volume named “Main Volume” and the second for a 100 GB volume named “Second Volume”. 
     The volume configurations discovery process may begin when the protocol is in Idle state  460 . At this point, a client may send a GetVolumeConfigs request  822  to the backup server, the request including a machineGuid parameter that uniquely identifies a machine. Upon receipt of the GetVolumeConfigs request  822  by the backup server the protocol transitions to AwaitingVolumeConfigs state  820 . While the protocol is in state  820 , the backup server sends zero or more VolumeConfig responses  823 , each response including a friendlyName parameter that uniquely identifies a volume associated with the machine. Once all of the VolumeConfig responses  823  are sent to the client, the backup server sends an EndVolumeConfigs response  825  to the client and the protocol transitions back to Idle state  460 . 
       FIG. 8   c  is a block diagram showing example protocol state transitions and messages for discovering any volume backups in a specific backup set for a particular machine that are stored in a backup server&#39;s database. A volume backup is a backup of a particular volume. A backup database may include backups of multiple different volumes in a specific backup set for a particular machine. For example, a backup database may include two different volume backups in the backup set created on January 10 th  starting at 9:30 pm for machine A: the first volume backup for a 200 GB volume named “Main Volume” and the second for a 100 GB volume named “Second Volume”. 
     The volume backup discovery process may begin when the protocol is in Idle state  460 . At this point, a client may send a GetVolumes request  832  to the backup server, the request including a machineGuid parameter that uniquely identifies a machine and a backupSetIndex parameter that uniquely identifies a specific backup set for the machine. Upon receipt of GetVolumes request  832  by the backup server the protocol transitions to AwaitingVolumes state  830 . While the protocol is in state  830 , the backup server sends zero or more Volume responses  833 , each response including a friendlyName parameter that uniquely identifies a volume backup in the backup set of the machine. Once all of the Volume responses  823  are sent to the client, the backup server sends an EndVolumes response  835  to the client and the protocol transitions back to Idle state  460 . 
       FIG. 8   d  is a block diagram showing example protocol state transitions and messages for establishing a backup schedule for a particular machine. Such a backup schedule may be stored in a backup server&#39;s database. For example, a schedule may be established to perform a backup of a particular machine every other day starting at 11:30 pm. 
     The establishment of a backup schedule may begin when the protocol is in Idle state  460 . At this point, a client machine may send a SetBackupSchedule request  842  to the backup server, the request including a machineGuid parameter that uniquely identifies the machine and scheduleDays and scheduleMinutes parameters that identify specific days of the week and a time to start a backup operation on the machine. Upon receipt of SetBackupSchedule request  842  by the backup server the protocol transitions to AwaitingSetBackupScheduleResponse state  840 . While the protocol is in state  840 , the backup server sends a SetBackupSchedule response  843  indicating the backup schedule for the machine has been established and stored in the backup database. Once the SetBackupSchedule response  843  is sent to the client the protocol transitions back to Idle state  460 . 
       FIG. 9  is a block diagram showing example protocol state transitions and messages for restoring a particular machine. For example, a restore may be performed using a backup set created on January 10 th . Or, only the volume on a machine named “Main Volume” may be restored from a backup set created on July 23 rd . 
     The restore process may begin when the protocol is in Idle state  460 . At this point, a client may send a BeginRestore request  912  to the backup server, the request including a machineGuid parameter that uniquely identifies a machine, a backupSetIndex parameter that uniquely identifies a specific backup set for the machine, and a uniqueIdentifier that uniquely identifies a volume in the backup set. Upon receipt of BeginRestore request  912  by the backup server, the protocol transitions to AwaitingBeginRestore state  910 . 
     While the protocol is in AwaitingBeginRestore state  910 , the backup server may send one or more Waiting responses  613  to the client if there will be a delay in performing the requested operation. The backup server may also send one or more Working responses  623 , indicating that it is currently busy working on an operation. While the protocol is in to AwaitingBeginRestore state  910 , if unable to perform the requested restore operation due to a failure, the backup server sends a BeginRestoreFailed response  913  including a reason parameter describing the reason for the failure. Otherwise, when not delayed or busy while in AwaitingBeginRestore state  910 , the backup server sends a BeginRestore response  915  to the client and the protocol transitions to Restoring state  920 . 
     While the protocol is in Restoring state  920 , the client sends zero or more GetClusters requests  922  to the backup server, each request requesting the backup server to send backed-up data. In once example, GetClusters request  922  requests the backup server to send the backed-up contents of a range of clusters. In response to each request  922 , the backup server sends a ClusterData response  923  including at least a portion of the requested cluster contents. The backup server may also send a ClusterDataBad response  925  indicating that at least a portion of the requested cluster contents is unavailable for some reason, such as due to an input/output (“I/O”) error or the like. The backup server may also send a ClusterDataMissing response  927  indicating that at least a portion of the requested cluster contents was not included in the backup for some reason, such as the clusters where not in use on the machine at the time of the backup, or the like. While the protocol is in Restoring state  920 , and once all GetClusters request  922  have been sent, the client sends an EndRestore request  924  to the backup server and the protocol transitions to AwaitingEndRestore state  930 . 
     While the protocol is in AwaitingEndRestore state  930 , the backup server sends an EndRestore response  933  to the client indicating that all requested cluster contents have been sent. Once the EndRestore response  933  has been sent to the client the protocol transitions back to Idle state  460  and the requested restore operation is complete. 
       FIG. 10  is a block diagram showing example phases of a 5 phased cluster-based backup operation.  FIGS. 11-15  are block diagrams showing an example cluster-based backup operation. The simplified example backup process described in connection with  FIG. 5  and the protocol state transitions and messages described in connection with  FIGS. 6 and 7  can be further described as an example 5-phase cluster-based backup operation as shown in  FIGS. 11-15 , the operation being divided into 5 phases as a matter of convenience and not limitation.  FIGS. 11-15  divide the operations of the various phases into those that occur on a client and those that occur on a backup server, as indicated by the Client column and the Backup Server column shown of the figures. 
       FIG. 11  is a block diagram showing Phase  1  of an example cluster-based backup operation. After the client has established a protocol session with the backup server, requested the start of a backup operation, indicated the volumes to backup, and provided volume configuration information, then Phase  1  begins at block  1110  with respect to the first volume to be backed up. 
     At block  1110 , the backup server retrieves from its backup database a set of previous file record hashes from the last backup created of the volume, if any, and sends the set to the client. In one example, the previous file record hashes are sent to the client using FileRecordHash response messages. The set of previous file record hashes represent the state of the volume&#39;s files system at the time of the previous backup. If there was no previous backup, then no previous file record hashes are sent to the client. In this case a complete backup is generally performed. Otherwise an incremental backup is generally performed unless nothing has changed on the volume since the previous backup. 
     At block  1112 , the client scans the file system of the volume, reads the file records into a “new file record list”, and calculates a set of new file record hashes from the new file record list. The set of new file record hashes represents the current state of the volume&#39;s file system. The scanning, reading, and calculating may occur while the backup server is sending the previous set to the client. In one example, a point-in-time copy of the volume is used for the foregoing and subsequent backup operations, such as produced by Volume Shadow Copy Service (“VSS”) or the like. 
     At block  1114 , the client compares the sets of new and previous file record hashes to determine if there have been any changes on the volume. If not, as indicated by block  1116 , then Phase  1  and the entire backup operation for the unchanged volume is done. If something has changed on the volume, then Phase  1  continues at block  1118 . 
     At block  1118 , the client builds a list of the clusters on the volume that are in-use, resulting in a “current in-use clusters list”. Clusters that are not currently in-use are typically not included in the backup operation. In addition, clusters containing data from ephemeral files that contain temporary data, cached data, and the like may be marked as not-in-use by removing them from the current in-use clusters list. Specific examples of such files include “pagefile.sys” and “hiberfil.sys” as typically used by various versions of the Microsoft Windows operating system. Any such ephemeral file and the clusters it is comprised of may be marked as not-in-use. Such files may be determined automatically by the backup system, may be specified as part of a backup configuration, and/or may be specified by a user and/or administrator of the backup system. 
     Also, at block  1118 , the client builds a list of clusters that are unchanged since the previous backup, resulting in a “current unchanged clusters list”. In one example, if a new file record hash is unchanged compared to the corresponding previous file record hash, then the clusters associated with the new file record hash are assumed to be unchanged. 
     At block  1120 , the client determines which clusters on the volume have potentially changed since the previous backup, building a “potentially changed clusters list”. In one example, this is done by determining which clusters are associated with file records that have changed since the previous backup. 
     At block  1122 , the client builds a “fix-up list” that is used to modify the content of clusters, and applies the fix-up list to the potentially changed clusters. The fix-up list indicates which clusters should have their content modified and how the content should be modified; such a list may be empty. In one example, the portion of a cluster after the end of a file stored in the cluster is set to zero, or some other pre-determined value. In another example, a file record may be marked so as to indicate that the file it represents is not-in-use. In another example, a file record may be marked so as to indicate that the folder it represents is empty. Typically, file records in the new file record list are marked rather than the file records on the volume. In yet another example, the contents of a cluster may be partially or completely replaced. Such operations may be performed prior to when file record hashes and/or cluster hashes are calculated. Such fix-up operations are typically performed on clusters in lists, such as the current in-use clusters list, the current unchanged clusters list, the potentially changed clusters list, and the like, rather than on the volume itself. 
     At block  1124 , the client sends the set of new file record hashes to the backup server reflecting the state of the volume at the start of the backup operation. In one example, the new file record hashes are sent to the backup server using FileRecordHash request messages. 
     At block  1126 , the backup server receives and stores the set of new file record hashes from the client, and the backup process transitions to Phase  2  as indicated by block  1128 . In one example, the set of new file record hashes is stored in the backup database and becomes the previous set upon successful completion of the backup operation. 
       FIG. 12  is a block diagram showing Phase  2  of the example cluster-based backup operation. The transition from Phase  1  to Phase  2  is indicated by block  1210  with Phase  2  beginning at block  1212 . 
     At block  1212 , after applying the fix-up list, if any, and excluding any clusters marked as not-in-use, the client calculates a cluster hash for each of the remaining potentially changed clusters. The hash calculations result in a “set of current cluster hashes”. In one example, a cluster hash is calculated by first applying any appropriate fix-ups to the cluster content and then providing the fixed-up cluster content as an input value to an MD5 hashing function, resulting in a cluster output value. Alternatively, any other appropriate function as described above for calculating hash values may be used. 
     At block  1214 , the client sends the set of current cluster hashes to the backup server. In one example, the current cluster hashes are sent to the backup server using ClusterHash request messages. In another example, the current cluster hashes are sent in increasing order of cluster index. For example, when sending cluster hashes for the first 5 clusters on a volume, the cluster hash for the first cluster is sent first, the cluster hash for the second cluster is sent second, and so on until all 5 cluster hashes have been sent in cluster index order 0-4. The client also sends information from the unchanged cluster list to the backup server. In one example, the unchanged cluster list is scanned to determine contiguous ranges of unchanged clusters and the contiguous ranges are sent to the backup server using ClustersUnchanged request messages. 
     At block  1216 , the backup server receives the set of current cluster hashes and the information from the unchanged cluster list. 
     At block  1218 , the backup server reads records from a VolumeException data structure for the volume being backed up and builds a hash table with the contents of the data structure. The VolumeException data structure is described in more detail in connection with  FIG. 32 . 
     At block  1220 , the backup server reads and combines records including cluster hashes from a VolumeCluster data structure, a VolumeClusterLatest1 data structure, a VolumeClusterLatest2 data structure, and the set of current cluster hashes indicating potentially changed clusters, and merges the combined set of cluster hashes, except for any current cluster hashes representing clusters that have changed since the previous backup, into a new VolumeCluster data structure. Also resulting from the merge is a “set of changed cluster hashes” representing the cluster that have changed since the previous backup. In one example, the set of changed clusters is created by including hashes from the set of current cluster hashes that are not also in one or more of the VolumeCluster, VolumeClusterLatest1, and VolumeClusterLatest2 data structures, which are described in connection with  FIGS. 30 and 31 . 
     At block  1222 , the backup server sorts the set of changed cluster hashes resulting in a “set of sorted changed cluster hashes”. In one example, the set of changed cluster hashes is first structured as (index, hash) pairs and then sorted in index order, where index is the cluster&#39;s index on the volume and hash is the corresponding cluster hash. Any type of sort may be used. In one example, the sort is a virtual-memory and cache-aware sort of the type described in U.S. patent application Ser. No. 11/407,783 filed on Apr. 20, 2006 and herein included by reference in its entirety. At this point the backup process transitions to Phase  3  as indicated by block  1224 . 
       FIG. 13  is a block diagram showing Phase  3  of the example cluster-based backup operation. The transition from Phase  2  to Phase  3  is indicated by block  1310  with Phase  3  beginning at block  1312 . 
     At block  1312 , the backup server reads and combines records including cluster hashes from a GlobalCluster data structure, a GlobalClusterLatest data structure, and the set of sorted changed cluster hashes, and merges the combined set of cluster hashes into a new GlobalCluster data structure such that the resulting new GlobalCluster data structure that contains only one record for each unique hash from the combined set of cluster hashes that were merged. The GlobalCluster data structure and GlobalClusterLatest data structure are described in more detail in connection with  FIGS. 24 and 25 . 
     At block  1314 , the backup server determines if there were multiple records with the same cluster hash in the combined set of cluster hashes. If not, then the backup process transitions to Phase  4  as indicated by blocks  1316  and  1320 . If there are records with the same cluster hash, then the process continues at block  1318 . 
     At block  1318 , when there are records with the same cluster hash, the backup server adds a copy of the duplicated records to the VolumeException data structure, and the process transitions to Phase  4  as indicated by block  1320 . The VolumeException data structure is described in more detail in connection with  FIG. 32 . 
       FIG. 14  is a block diagram showing Phase  4  of the example cluster-based backup operation. The transition from Phase  3  to Phase  4  is indicated by block  1410  with Phase  4  beginning at block  1412 . 
     At block  1412 , the backup server scans the set of sorted changed cluster hashes and determines which of the cluster hashes from the set represent cluster contents already stored by the backup server. Cluster hashes from the set that are already stored by the backup server are added to a VolumeClusterLatest1 data structure. The VolumeClusterLatest1 data structure is described in more detail in connection with  FIG. 31 . 
     At block  1414 , the backup server scans the set of sorted changed cluster hashes and determines which of the cluster hashes from the set represent cluster contents that are not already stored by the backup server and creates a set of needed cluster hashes. 
     At block  1424 , the backup server coalesces the set of needed cluster hashes into a list of contiguous ranges of needed clusters. 
     At block  1418 , the backup server sends each contiguous range of needed clusters to the client. In one example, this is done by sending a NeedClusterData response message to the client for each continuous range of clusters needed. 
     At block  1420 , the client receives each contiguous range of needed clusters from the backup server and reads the content of the needed clusters from the volume being backed up. 
     At block  1422 , the client sends the needed cluster contents to the backup server. In one example, this is done by sending a ClusterData request message to the backup server for each continuous range of clusters needed. 
     At block  1424 , the backup server adds each of the cluster contents received from the client to a GlobalData data structure, calculates a cluster hash for each of the received cluster contents, adds records including the cluster hash representing each cluster contents to a VolumeClusterLatest2 data structure, sorts the records including the calculated cluster hashes, and the process transitions to Phase  5  as indicated by block  1426 . The VolumeClusterLatest2 data structure is described in more detail in connection with  FIG. 31 . 
       FIG. 15  is a block diagram showing Phase  5  of the example cluster-based backup operation. The transition from Phase  4  to Phase  5  is indicated by block  1510  with Phase  5  beginning at block  1512 . 
     At block  1512 , the backup server stores the sorted records in a GlobalClusterLatest data structure, commits the backup of the volume, and the backup process is complete. The GlobalClusterLatest data structure is described in more detail in connection with  FIG. 25 . 
       FIG. 16  is a block diagram showing an example commit operation for a backup operation. Once a backup operation is complete, as indicated by block  1610 , the data structures for the backup may be stored in the backup server database using a commit operation. Should a failure occur during the store, the commit operation can provide the ability to recover from the failure. In one example, the commit operation makes use of a Commit data structure, such as described in connection with  FIG. 19 , including records for the various backup data structures being stored and a commit flag. 
     At block  1612 , the backup server flushes the backup data structures to the backup database. 
     At block  1614 , the backup server adds a record to the Commit data structure for each backup data structure being stored. The backup server then flushes the Commit data structure to the backup database. 
     At block  1616 , the backup server sets the commit flag in the Commit data structure, and then flushes the Commit data structure to the backup database. 
     At block  1618 , the backup server sets a new stream index as appropriate for each of the backup data structures that make use of a stream index. The backup server then flushes the Commit data structure to the backup database. 
     At block  1620 , the backup server renames the backup data structures as appropriate, and then flushes the Commit data structure to the backup database. In one example, any backup data structures maintained as files with a “.new” file name extension are renamed with a “.dat” extension after any existing “.dat” files of the same name are deleted. 
     At block  1622 , the backup server clears the commit flag in the Commit data structure, and then flushes the Commit data structure to the backup database. 
     At block  1624 , the commit operation is complete and the backup data structures have been stored. 
     In one example, whenever the backup server starts, it reads the Commit data structure from the backup database. If a failure occurred during a previous commit operation, such as the backup server losing power or the like, and at startup time finds the commit flag set, then the backup server assumes there was a failure during the previous commit operation. In this case, the backup server repeats the work done indicated by blocks  1618  through  1624  to salvage the previously failed commit operation. 
       FIG. 17  is a block diagram showing an example cluster-based restore operation for restoring a partial or complete backup from a backup server to a client. The restore operation may be started by a user or automatically. Once the client has established a protocol session with the backup server and requests a restore, the client begins the restore operation as indicated by block  1712 . In one example, the client requests a restore using a BeginRestore request message. 
     At block  1712 , the client requests the desired backup data to be restored. In one example, the client sends one or more GetClusters request messages, each specifying a specific contiguous range of cluster contents to be restored. 
     At block  1714 , the backup server determines the specific volume backup containing the clusters requested for restore by the client and begins creating a map of backed-up volume clusters. In one example, each entry in the cluster map includes a cluster&#39;s volume index and a pointer to the backed-up contents for the cluster in the backup database. In another example, the map includes a count of contiguous cluster contents starting at the pointer, with one entry in the map for each set of contiguous clusters on the backup server. The map may be created by merging data from VolumeCluster, VolumeClusterLatest, and VolumeException data structures. 
     At block  1716 , the backup server checks the map for specific cluster contents requested by the client. In one example, the backup server may not yet find the requested clusters listed in the map and may delay the check while continuing to build the cluster map. 
     At block  1718 , once the requested clusters are listed in the map, the backup server reads the specific cluster contents from the backup database and sends the contents to the client. In one example, this is done using a ClusterData response message. Should the requested cluster data be missing from the backup, the backup server may send a ClusterDataMissing response message to the client. Should the backup server be unable to read requested cluster data from the backup database, the backup server may send a ClusterDataBad response message to the client. 
     At block  1720 , the client receives cluster contents from the backup server and restores the contents to the volume being restored. 
     At block  1724 , if more cluster contents are required to complete the restore, the process continues at block  1712  where the client may request additional cluster content and/or wait for cluster contents to be received from the backup server in response to requests already sent. If all requested cluster contents have been restored, then the process is complete as indicated by block  1726 . 
       FIG. 18  is a block diagram showing an example backup database  1800  including example data structures of which it is comprised. Example Control data structure  1852  maintains information about the client machine and volume most recently backed up. Example Machines data structure  1854  identifies the various client machines for which backups are maintained in backup database  1800 . Example VolumeConfig data structure  1856  identifies the various volumes for which backups are maintained in backup database  1800 . Example BackupSet data structure  1858  identifies the various backup sets maintained in backup database  1800 . The remaining example data structures may be organized into one of several sets: 
     Per backup database data structures: in one example, there is a single instance of this set of data structures  1810  per backup database  1800 . In one example, per backup database set  1810  is comprised of a Commit data structure. 
     Per cluster-size data structures: in one example, there is one instance of this set of data structures  1820  for each different cluster size that is backed up in the backup database  1800 . For example, a volume backed up from one client may have a 2048 byte cluster size. Volumes backed up from a second client may have cluster sizes of 4096 bytes and 2048 bytes. In this case, there is one set of per cluster-size data structures  1820  for each of the two cluster sizes of 2048 bytes and 4096 bytes. In one example, each per cluster-size set  1820  is comprised of a GlobalCluster data structure  1822 , a GlobalClusterLatest data structure  1824 , an Index data structure  1826 , and a Data data structure  1828 . 
     Per volume data structures: in one example, there is one instance of this set of data structures  1830  for each client volume that is backed up in backup database  1800 . For example, if client machine “Client1” includes volumes “Vol1” and “Vol2” that are both backed up, then backup database  1800  includes one per volume set  1830  for Vol1 and another per volume set  1830  for Vol2. In one example, per volume set  1830  include a Volume data structure. 
     Per volume-cluster-size data structures: in one example, there is one instance of this set of data structures  1840  for each different cluster size of each volume that is backed up in the backup database  1800 . For example, if Vol1 having as cluster size of 2048 bytes was backed up, then backup database  1800  includes one per volume-cluster-size set  1840  for Vol1 with a 2048 byte cluster size. If Vol1 is subsequently modified to have a 4096 byte cluster size (such as via replacement, reformatting, or the like) and is again backed up, then backup database  1800  further includes a per volume-cluster-size set  1840  for Vol1 with a 4096 byte cluster size. In one example, per volume-cluster-size set  1840  includes a FileRecordHash data structure  1842 , a VolumeCluster data structure  1844 , a VolumeClusterLatest data structure  1846 , and a VolumeException data structure  1848 . 
     In one example, each of the foregoing example data structures is implemented as a file with each file including: a fixed header providing information about the file including a “file type”, the number of data streams included in the file, the size of the data stream chunks if multiple data streams, a data stream sequence number, and a current data stream indicator or index; a file-specific header including a description of the specific set the data structure file is a part of; an extensible markup language (“XML”) description of the schema of the file; and one or more streams of data. 
       FIG. 19  is an XML description showing the schema of an example Commit data structure  1812 . In one example, Commit data structure  1812  is implemented as a file and is used to commit backup data at the end of a backup operation. 
     Header section  1910  includes a Committed field  1911  that is set and reset as part of the commit operation described in connection with  FIG. 16 . Record section  1920  includes a FileName field  1921  indicating the file name of a data structure file being created, updated, or deleted as part of a backup operation and a StreamIndex field  1922  indicating the index of the data structure file&#39;s current data stream. The Commit data structure  1812  file is named using the format: “Commit.dat”. 
     Alternatively, in another example, Commit data structure  1812  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 20  is an XML description showing the schema of an example Control data structure  1852 . In one example, Control data structure  1852  is implemented as a file and is used to maintain information about the client machine and volume most recently backed up. Once such file is maintained for each different volume cluster size. 
     Header section  2010  includes a BytesPerCluster field  2011  indicating the cluster size of the volume, a NextIndex field  2012  indicating the next available index in the Index data structure  1826 , and a NextDataOffset field  2013  indicating the offset of the next available cluster content data location in the Data data structure  1828 . 
     Control data structure  1852  files are named using the format: “Control.&lt;size&gt;.dat” where size is the volume cluster size in bytes. For example, for a volume with a cluster size of 4096 bytes, the associated Control data structure  1852  file would be named: “Control.4096.dat”. 
     Alternatively, in another example, Control data structure  1852  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 21  is an XML description showing the schema of an example Machines data structure  1854 . In one example, Machines data structure  1854  is implemented as a file and is used to maintain information about the client machines for which backups are maintained in the backup database. 
     One record section  2110  is included in the Machines data structure  1854  file for each client machine known to the backup database. Each machine record  2110  includes: a MachineGuid field  2111  uniquely identifying the client machine; a ScheduleDays field  2112  and a ScheduleMinutes field  2113  identifying the machine&#39;s backup schedule in days of the week and time in minutes after midnight, local time; and a MacAddress field  2114  identifying the machine&#39;s unique Media Access Control (“MAC”) address. The Machines data structure  1854  file is named using the format: “Machines.dat”. 
     Alternatively, in another example, Machines data structure  1854  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 22  is an XML description showing the schema of an example VolumeConfig data structure  1856 . In one example, volumeConfig data structure  1856  is implemented as a file and is used to maintain information about client machine volumes backed up in the backup database. The backup server maintains one such file for each client machine for which volume configurations are defined. 
     Header section  2210  includes a MachineGuid field  2211  to uniquely identify the client machine associated with the VolumeConfig data structure  1856  file&#39;s volume configuration information. Each record section  2220  includes information defining and uniquely identifying a volume associated with the client machine uniquely identified by MachineGuid  2211 . One such record section  2220  exists for each defined volume. 
     VolumeConfig data structure  1856  files are named using the format: “&lt;machine&gt;.VolumeConfig.dat” where machine is the name of the client machine for which the volume data is defined. For example, for a machine named “Client1”, the associated VolumeConfig data structure  1856  file would be named: “Client1.VolumeConfig.dat”. 
     Alternatively, in another example, VolumeConfig data structure  1856  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 23  is an XML description showing the schema of an example BackupSet data structure  1858 . In one example, BackupSet data structure  1858  is implemented as a file and is used to maintain a list of all backup sets stored in the backup database for a specific client machine. 
     Header section  2310  includes a MachineGuid field  2311  to uniquely identify the client machine associated with the backup sets. Each record section  2320  includes information defining and uniquely identifying a backup set associated with the client machine uniquely identified by MachineGuid  2311 . One such record section  2320  exists for each backup set associated with the client machine stored in the backup database. 
     BackupSet data structure  1858  files are named using the format: “&lt;machine&gt;.BackupSet.dat” where machine is the name of the client machine for which the backup set is defined. For example, for a machine named “Client1”, the associated BackupSet data structure  1858  file would be named: “Client1.Backup.dat”. 
     Alternatively, in another example, BackupSet data structure  1858  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 24  is an XML description showing the schema of an example GlobalCluster data structure  1822 . In one example, GlobalCluster data structure  1822  is implemented as a file and is used to store one record for each unique cluster in the backup database, excluding the clusters that were added by the most recent backup. There is one such file for each different cluster size stored in the backup database. 
     Header section  2410  includes a BytesPerCluster field  2411  to identify the cluster size associated with the GlobalCluster data structure  1822  file. Each record section  2420  includes information uniquely identifying a cluster stored in the backup database including a Hash field  2421  that is an MD5 hash of the cluster contents and a DataIndex field  2422  that references the associated cluster contents in the Data data structure  1828  of the backup database. One such record section  2420  exists for each cluster stored in the backup database. 
     GlobalCluster data structure  1822  files are named using the format: “GlobalCluster.&lt;size&gt;.dat” where size is the cluster size in bytes of the cluster associated with the file. For example, for a cluster size of 4096 bytes, the associated GlobalCluster data structure  1822  file would be named: “GlobalCluster.4096.dat”. 
     Alternatively, in another example, GlobalCluster data structure  1822  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 25  is an XML description showing the schema of an example GlobalClusterLatest data structure  1824 . In one example, GlobalClusterLatest data structure  1824  is implemented as a file and is used to store one record for each unique cluster in the backup database that was added by the most recent backup. There is one such file for each different cluster size stored in the backup database. 
     Header section  2510  includes a BytesPerCluster field  2511  to identify the cluster size associated with the GlobalClusterLatest data structure  1824  file. Each record section  2520  includes information uniquely identifying a cluster stored in the backup database including a Hash field  2521  that is an MD5 hash of the cluster contents and a DataIndex field  2522  that references the associated cluster contents in the Data data structure  1828  of the backup database. One such record section  2520  exists for each cluster stored in the backup database. 
     GlobalClusterLatest data structure  1824  files are named using the format: “GlobalClusterLatest.&lt;size&gt;.dat” where size is the cluster size in bytes of the cluster associated with the file. For example, for a cluster size of 4096 bytes, the associated GlobalClusterLatest data structure  1824  file would be named: “GlobalClusterLatest.4096.dat”. 
     Alternatively, in another example, GlobalClusterLatest data structure  1824  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 26  is an XML description showing the schema of an example Index data structure  1826 . In one example, Index data structure  1826  is implemented as a file and is used to store one record for each unique cluster or a particular size stored in the backup database, plus one record at the end indicating the next available record location. There is one such file for each different cluster size stored in the backup database. 
     Header section  2610  includes a BytesPerCluster field  2611  identifying the cluster size associated with the Index data structure  1826  file. Record section  2620  includes a ByteOffset field  2621  representing a cluster and indicating the offset of the cluster contents in the Data data structure  1828 . One such record section  2620  exists for each cluster stored in the backup database. Record sections  2620  are typically added to the Index data structure  1826  file in the same order cluster data is added to the Data data structure  1828  of the backup database. The length of a cluster is implied by the offset of the following cluster. Once a record  2620  is added it is typically not changed, except when recovering space from deleted backups. 
     Index data structure  1824  files are named using the format: “Index.&lt;size&gt;.dat” where size is the cluster size in bytes of the cluster associated with the file. For example, for a cluster size of 4096 bytes, the associated Index data structure  1824  file would be named: “Index.4096.dat”. 
     Alternatively, in another example, Index data structure  1824  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 27  is an XML description showing the schema of an example Data data structure  1828 . In one example, Data data structure  1828  is implemented as a file and is used to store one record for each unique cluster of a particular size stored in the backup database. There is one such file for each different cluster size stored in the backup database. 
     Header section  2710  includes a bytesPerCluster field  2711  identifying the cluster size associated with the Data data structure  1828  file. Record section  2720  includes a ClusterData field  2721  containing the content of a cluster. One such record section  2720  exists for each cluster stored in the backup database. The length of a cluster is implied by the offset of the cluster compared to the offset of the next cluster as indicated in the Index data structure  1826  file. Record sections  2720  are typically added to the Data data structure  1828  file in the order received from the client. Once a record  2720  is added it is typically not changed, except when recovering space from deleted backups. 
     Data data structure  1828  files are named using the format: “Data.&lt;size&gt;.dat” where size is the cluster size in bytes of the cluster associated with the file. For example, for a cluster size of 4096 bytes, the associated Data data structure  1828  file would be named: “Data.4096.dat”. 
     Alternatively, in another example, Data data structure  1828  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 28  is an XML description showing the schema of an example Volume data structure  1832 . In one example, Volume data structure  1832  is implemented as a file and is used to store each backup version of the volume. There is one such file for each different volume backed up in the backup database. 
     Header section  2810  includes a MachineGuid field indicating the client machine and a UniqueId field indicating the backed up volume associated with the machine. Record section  2820  includes a BackupSetIndex field indicating the backup set of which the backup version identified by record  1829  is a part. Record section  2820  also includes a Version field indicating the specific version of the backup identified by record  1829 . One such record section  2820  exists for each backup version of the volume that is stored in the backup database with the records typically stored in increasing order of version number. 
     Volume data structure  1858  files are named using the format: “&lt;machine&gt;.&lt;volume&gt;.Volume.dat” where machine is the name of the client machine and volume is the backed up volume. For example, for a machine named “Client1” with a volume named “Vol1”, the associated Volume data structure  1858  file would be named: “Client.Vol1.Volume.dat”. 
     Alternatively, in another example, Volume data structure  1858  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 29  is an XML description showing the schema of an example FileRecordHash data structure  1842 . In one example, FileRecordHash data structure  1842  is implemented as a file and is used to store file record hashes of the most recent volume backup. There is one such file for each different volume and volume cluster size backed up in the backup database. 
     Header section  2910  includes a MachineGuid field  2911  indicating the client machine, a UniqueId field  2912  indicating the volume associated with the machine, and a BytesPerCluster field  2913  indicating the cluster size of the volume. Record section  2920  includes an Index field  2921  indicating the index number of a file record in the volume&#39;s file system and a Hash field  2922  storing a hash of the file record associated with the index number. 
     FileRecordHash data structure  1842  files are named using the format: “&lt;machine&gt;.&lt;volume&gt;.FileRecordHash.&lt;size&gt;.dat” where machine is the name of the client machine, and volume is the volume associated with the machine, and size is the cluster size of the volume. For example, for a machine named “Client1” with a volume named “Vol1” with a 2048 cluster size, the associated FileRecordHash data structure  1842  file would be named: “Client1.Vol1.FileRecordHash.2048.dat”. 
     Alternatively, in another example, FileRecordHash data structure  1842  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 30  is an XML description showing the schema of an example VolumeCluster data structure  1844 . In one example, VolumeCluster data structure  1844  is implemented as a file and is used to store one record for each version of each cluster of a volume that has been backed up, excluding the most recent backup. There is one such file for each different volume and volume cluster size backed up in the backup database. 
     Header section  3010  includes a MachineGuid field  3011  indicating the client machine, a UniqueId field  3012  indicating the volume associated with the machine, and a BytesPerCluster field  3013  indicating the cluster size of the volume. Record section  3020  includes: a ClusterIndex field  3021  indicating the cluster index associated with a record  3020 ; a LowestVersion field  3022  indicating the lowest backup version number to which the record  3020  applies; a HighestVersion field  3023  indicating the highest backup version number to which the record  3020  applies; a Hash field  3024  storing a hash of the cluster associated with the cluster index; and a DataIndex field  3025  pointing to the cluster stored in the Data data structure  1828 . There is one such record  3020  for each version of each cluster on a backed up volume, excluding clusters in the latest backup that changed from the previous backup. 
     VolumeCluster data structure  1842  files are named using the format: “&lt;machine&gt;.&lt;volume&gt;.VolumeCluster.&lt;size&gt;.dat” where machine is the name of the client machine, and volume is the volume associated with the machine, and size is the cluster size of the volume. For example, for a machine named “Client1” with a volume named “Vol1” with a 2048 cluster size, the associated VolumeCluster data structure  1842  file would be named: “Client1.Vol1.VolumeCluster.2048.dat”. 
     Alternatively, in another example, VolumeCluster data structure  1842  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 31  is an XML description showing the schema of an example VolumeClusterLatest data structure  1858 . In one example, VolumeClusterLatest data structure  1858  is implemented as two files that are used to store one record for each cluster of the current volume backup, excluding clusters unchanged from the previous backup. The first of the two files (indicated by a “1” in the file name) includes records for those clusters of the volume that were already present in the backup database, typically from a different client. The second of the two files (indicated by a “2” in the file name) includes records for those clusters of the volume for which the cluster content was not already present in the backup database. 
     Header section  3110  includes a MachineGuid field  3111  indicating the client machine, a UniqueId field  3112  indicating the volume associated with the machine, a BytesPerCluster field  3113  indicating the cluster size of the volume, and a BackupSetIndex field  3114  indicating the backup set of which the VolumeClusterLatest data structure  1858  file is a part. Record section  3020  includes: a ClusterIndex field  3121  indicating the cluster index associated with a record  3020 ; a Hash field  3122  storing a hash of the cluster associated with the cluster index; and a DataIndex field  3123  pointing to the cluster stored in the Data data structure  1828 . There is one such record  3120  for each cluster in the latest backed up the volume. 
     VolumeClusterLatest data structure  1842  files are named using the format: “&lt;machine&gt;.&lt;volume&gt;.VolumeCluster&lt;n&gt;.&lt;size&gt;.dat” where machine is the name of the client machine, and volume is the volume associated with the machine, and size is the cluster size of the volume, and n is either “1” or “2”. For example, for a machine named “Client1” with a volume named “Vol1” with a 2048 cluster size, the associated pair of VolumeClusterLatest data structure  1842  files would be named: “Client1.Vol1.VolumeCluster1.2048.dat” and “Client1.Vol1.VolumeCluster2.2048.dat”. 
     Alternatively, in another example, VolumeClusterLatest data structure  1842  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 32  is an XML description showing the schema of an example VolumeException data structure  1848 . In one example, VolumeException data structure  1848  is implemented as a file and is used to store clusters received from the client but later determined to already exist in the backup database. There is one such file for each different volume and volume cluster size backed up in the backup database. 
     Header section  3210  includes a MachineGuid field  3211  indicating the client machine, a UniqueId field  3212  indicating the volume associated with the machine, a BytesPerCluster field  3213  indicating the cluster size of the volume, and a BackupSetIndex field  3214  indicating the backup set of which the VolumeException data structure  1848  file is a part. Record section  3120  includes an OldClusterIndex field  3221  indicating the location of the original cluster in Data data structure  1828  and a NewClusterIndex field  3222  indicating the location of the duplicate cluster in Data data structure  1828 . 
     VolumeException data structure  1848  files are named using the format: “&lt;machine&gt;.&lt;volume&gt;.VolumeException.&lt;size&gt;.dat” where machine is the name of the client machine, and volume is the volume associated with the machine, and size is the cluster size of the volume. For example, for a machine named “Client1” with a volume named “Vol1” with a 2048 cluster size, the associated VolumeException data structure  1848  file would be named: “Client1.Vol1.VolumeException.2048.dat”. 
     Alternatively, in another example, VolumeException data structure  1848  may be titled differently, may include equivalent fields named and/or structured differently, may be combined with other data structures, or may be implemented in various other forms. 
       FIG. 33  is a block diagram showing example relationships between a portion of the per cluster-size  1820  data structures. These relationships provide for the organization and efficient storage and access of backup data. One such set of data structures  1820  exists for each cluster size stored in the backup database. 
     Control data structure  1852  includes: NextIndex field  2012  that indicates, as illustrated by pointer  3382 , the next available record location Offset next    3349  in Index data structure  1826 ; and NextDataOffset field  2013  that indicates, as illustrated by pointer  3383 , the next available record location D next    3359  in Data data structure  1828 . 
     GlobalCluster data structure  1822  is comprised of records, each record including a cluster hash Hash field  2421  associated with a DataIndex field  2422  pointing to a cluster offset stored in Index data structure  1826  that in turn points to cluster data stored in Data data structure  1828  that is uniquely identified by cluster hash  2421 . For example, GlobalCluster entry (H 0 , Idx 0 ) points  3384  to Index entry (Offset 0 ) which in turn points  3386  to Data entry (D 0 ). 
     GlobalCluster data structure  1822  stores one record for each unique cluster in the backup database, excluding the clusters that were added by the most recent backup. For example, before the beginning of the 17 th  backup, GlobalCluster data structure  1822  contains records for data added by backups version  1  through  15 , but not for backup version  16 . Thus, GlobalCluster entry (H n , Idx n ) represents the n th  record of backup version  15  and points  3385  to Index entry (Offset n ), the last index record of backup version  15 , which in turn points  3387  to Data entry (D n ), the last data record of backup version  15 . 
     Records in GlobalCluster data structure  1822  are typically ordered by the value of their Hash fields  2421 . Typically, each backup operation reads the entire GlobalCluster data structure  1822  sequentially and writes a new version of the structure. 
     Records are appended to in Index data structure  1826  in the order cluster data is received from a client. Once data is added to structure  1826  it is generally not changed, except when recovering space from deleted backups. Records are also appended to in Data data structure  1828  in the order cluster data is received from the client. Cluster data may be stored in a compressed or uncompressed format. Once data is added to structure  1828  it is generally not changed, except when recovering space from deleted backups. 
       FIG. 34  is a block diagram showing example relationships between the per cluster-size  1820  data structures as shown in  FIG. 33  with the addition of a GlobalClusterLatest data structure  1824 . GlobalClusterLatest data structure  1824  is comprised of records, each record  2520  including a cluster hash Hash field  2521  associated with a DataIndex field  2522  pointing to a cluster offset stored in Index data structure  1826  that in turn points to cluster data stored in Data data structure  1828  that is uniquely identified by cluster hash  2521 . For example, GlobalClusterLatest entry (H n+1 , Idx n+1 )  3429  points to Index entry (Offset n+1 )  3349  which in turn points  3386  to Data entry (D n+1 )  3459 . 
     GlobalClusterLatest data structure  1824  stores one record for each unique cluster in the backup database that was added by the most recent backup. For example, before the beginning of the 17 th  backup, GlobalClusterLatest data structure  1824  contains records for data added by backup version  16 , but not for backup versions  1 - 16 . Thus, GlobalClusterLatest entry (H n+m , Idx n+m )  3430  represents the m th  record of backup version  16  and points  3472  to Index entry (Offset n+m )  3450 , the last index record of backup version  16 , which in turn points  3474  to Data entry (D n+m )  3460 , the last data record of backup version  16 . 
     In first embodiments, a method for restoring a backup of a storage media comprises: (a) receiving a request for a cluster data, the request associated with the backup, a backup database comprising the backup, the backup database further comprising a plurality of cluster data, each of the plurality of cluster data being unique wherein single instance storage within the backup database is provided; (b) reading the cluster data from the backup database; and (c) providing the cluster data read from the backup database. 
     In second embodiments, the backup database of the first embodiments contains a plurality of backups, the plurality of backups associated with a plurality of machines. 
     In third embodiments, the backup database of the first embodiments comprises a set of cluster hashes, each cluster hash of the set of cluster hashes uniquely corresponding to one of the plurality of cluster data in the backup database, and each of the plurality of cluster data in the backup database uniquely corresponding to one of the cluster hashes in the set of cluster hashes. 
     In fourth embodiments, the backup of the first embodiments comprises a set of cluster indexes and a set of cluster hashes, each index of the set of cluster indexes corresponding to a single cluster hash of the set of cluster hashes, (b) the request of the first embodiments comprises a requested cluster index, and (c) the reading the cluster data is based at least in part on comparing the requested cluster index with the set of cluster indexes and determining the corresponding cluster hash of the set of cluster hashes. 
     In fifth embodiments, the method of the first embodiments comprises creating a cluster map comprising a count of contiguous available cluster data, wherein the providing further comprises providing a plurality of contiguous cluster data in a single response. 
     In sixth embodiments, the method of the first embodiments comprises providing an indication of missing cluster data if at least a portion of the requested cluster data is not included in the backup database. 
     In seventh embodiments, the method of the first embodiments comprises providing an indication of bad cluster data if at least a portion of the requested cluster data is unavailable. 
     In eighth embodiments, the clusters associated with the plurality of cluster data of the first embodiments are of a plurality of sizes. 
     In ninth embodiments, a computer-readable medium is encoded with computer-executable instructions embodying a method for restoring a backup of a storage media that when executed are configured to: (a) receive a request for a cluster data, the request associated with a backup, a backup database comprising the backup, the backup database further comprising a plurality of cluster data, each of the plurality of cluster data being unique wherein single instance storage within the backup database is provided; (b) read the cluster data from the backup database; and (c) provide the cluster data read from the backup database. 
     In tenth embodiments, the backup database of the ninth embodiments contains a plurality of backups, the plurality of backups associated with a plurality of machines. 
     In eleventh embodiments, the backup database of the ninth embodiments comprises a set of cluster hashes, each cluster hash of the set of cluster hashes uniquely corresponding to one of the cluster data in the backup database, each cluster data in the backup database uniquely corresponding to one of the cluster hashes in the set of cluster hashes. 
     In twelfth embodiments, (a) the backup of the ninth embodiments comprises a set of cluster indexes and a set of cluster hashes, each index of the set of cluster indexes corresponding to a single cluster hash of the set of cluster hashes; (b) the request of the ninth embodiments comprises a requested cluster index; and (c) the read of the cluster data of the ninth embodiment is configured at least in part to compare the requested cluster index with the set of cluster indexes and determine the corresponding cluster hash of the set of cluster hashes to read from the backup database. 
     In thirteenth embodiments, the method of the twelfth embodiments comprises creating a cluster map comprising a count of contiguous available cluster data, wherein the providing comprises providing a plurality of contiguous cluster data in a single response. 
     In fourteenth embodiments, the method of the ninth embodiments comprises providing an indication of missing cluster data if at least a portion of the requested cluster data is not included in the backup. 
     In fifteenth embodiments, the method of the ninth embodiments comprises providing an indication of bad cluster data if at least a portion of the requested cluster data is unavailable. 
     In sixteenth embodiments, the clusters associated with the plurality of cluster data of the ninth embodiments are of a plurality of sizes. 
     In seventeenth embodiments, a method for restoring a backup of a storage media comprises: (a) receiving a request for a cluster data, the request associated with a backup, the backup comprising a set of cluster indexes and a first set of cluster hashes, each index of the set of cluster indexes corresponding to a single cluster hash of the first set of cluster hashes, the backup associated with a backup database, the backup database comprising a first plurality of cluster data, the backup database further comprising a second set of cluster hashes, each of the second set of cluster hashes uniquely corresponding to one of the first plurality of cluster data, each of the first plurality of cluster data uniquely corresponding to one of the cluster hashes in the second set of cluster hashes, each of the first plurality of cluster data being unique wherein single instance storage within the backup database is provided; (b) reading the cluster data from the backup database; and (c) providing the cluster data read from the backup database. 
     In eighteenth embodiments, the method of the seventeenth embodiments comprises correlating a cluster index to a cluster hash of the first set of cluster hashes, based at least in part on the set of cluster indexes, the request comprising the cluster index, wherein the reading the cluster data from the backup database is based at least in part on the cluster hash. 
     In nineteenth embodiments, the requesting of the eighteenth embodiments comprises a cluster count, the cluster count indicating a count of contiguous cluster data requested. 
     In twentieth embodiments, the method of the nineteenth embodiments comprises creating a cluster map comprising a set of contiguous cluster data, based at least in part on the cluster index and the cluster count, wherein the provided cluster data comprises one of the set of contiguous cluster data. 
       FIG. 35  is a block diagram showing an example computing environment  3500  in which the technologies, processes, systems and methods described above may be implemented. A suitable computing environment may be implemented with numerous general purpose or special purpose systems. Examples of well known systems may include, but are not limited to, personal computers (“PC”), hand-held or laptop devices, microprocessor-based systems, multiprocessor systems, servers, workstations, consumer electronic devices, set-top boxes, and the like. 
     Computing environment  3500  generally includes a general-purpose computing system in the form of a computing device  3501  coupled to various peripheral devices  3502 ,  3503 ,  3504  and the like. System  3500  may couple to various input devices  3503 , including keyboards and pointing devices, such as a mouse or trackball, via one or more I/O interfaces  3512 . The components of computing device  3501  may include one or more processors (including central processing units (“CPU”), graphics processing units (“GPU”), microprocessors (“uP”), and the like)  3507 , system memory  3509 , and a system bus  3508  that typically couples the various components. Processor  3507  typically processes or executes various computer-executable instructions to control the operation of computing device  3501  and to communicate with other electronic and/or computing devices, systems or environment (not shown) via various communications connections such as a network connection  3514  or the like. System bus  3508  represents any number of several types of bus structures, including a memory bus or memory controller, a peripheral bus, a serial bus, an accelerated graphics port, a processor or local bus using any of a variety of bus architectures, and the like. 
     System memory  3509  may include computer readable media in the form of volatile memory, such as random access memory (“RAM”), and/or non-volatile memory, such as read only memory (“ROM”) or flash memory (“FLASH”). A basic input/output system (“BIOS”) may be stored in non-volatile or the like. System memory  3509  typically stores data, computer-executable instructions and/or program modules comprising computer-executable instructions that are immediately accessible to and/or presently operated on by one or more of the processors  3507 . 
     Mass storage devices  3504  and  3510  may be coupled to computing device  3501  or incorporated into computing device  3501  via coupling to the system bus. Such mass storage devices  3504  and  3510  may include a magnetic disk drive which reads from and/or writes to a removable, non-volatile magnetic disk (e.g., a “floppy disk”)  3505 , and/or an optical disk drive that reads from and/or writes to a non-volatile optical disk such as a CD ROM, DVD ROM  3506 . Alternatively, a mass storage device, such as hard disk  3510 , may include non-removable storage medium. Other mass storage devices may include memory cards, memory sticks, tape storage devices, and the like. 
     Any number of computer programs, files, data structures, and the like may be stored on the hard disk  3510 , other storage devices  3504 ,  3505 ,  3506  and system memory  3509  (typically limited by available space) including, by way of example, operating systems, application programs, data files, directory structures, and computer-executable instructions. 
     Output devices, such as display device  3502 , may be coupled to the computing device  3501  via an interface, such as a video adapter  3511 . Other types of output devices may include printers, audio outputs, tactile devices or other sensory output mechanisms, or the like. Output devices may enable computing device  3501  to interact with human operators or other machines or systems. A user may interface with computing environment  3500  via any number of different input devices  3503  such as a keyboard, mouse, joystick, game pad, data port, and the like. These and other input devices may be coupled to processor  3507  via input/output interfaces  3512  which may be coupled to system bus  3508 , and may be coupled by other interfaces and bus structures, such as a parallel port, game port, universal serial bus (“USB”), fire wire, infrared port, and the like. 
     Computing device  3501  may operate in a networked environment via communications connections to one or more remote computing devices through one or more local area networks (“LAN”), wide area networks (“WAN”), storage area networks (“SAN”), the Internet, radio links, optical links and the like. Computing device  3501  may be coupled to a network via network adapter  3513  or the like, or, alternatively, via a modem, digital subscriber line (“DSL”) link, integrated services digital network (“ISDN”) link, Internet link, wireless link, or the like. 
     Communications connection  3514 , such as a network connection, typically provides a coupling to communications media, such as a network. Communications media typically provide computer-readable and computer-executable instructions, data structures, files, program modules and other data using a modulated data signal, such as a carrier wave or other transport mechanism. The term “modulated data signal” typically means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communications media may include wired media, such as a wired network or direct-wired connection or the like, and wireless media, such as acoustic, radio frequency, infrared, or other wireless communications mechanisms. 
     Those skilled in the art will realize that storage devices utilized to provide computer-readable and computer-executable instructions and data can be distributed over a network. For example, a remote computer or storage device may store computer-readable and computer-executable instructions in the form of software applications and data. A local computer may access the remote computer or storage device via the network and download part or all of a software application or data and may execute any computer-executable instructions. Alternatively, the local computer may download pieces of the software or data as needed, or distributively process the software by executing some of the instructions at the local computer and some at remote computers and/or devices. 
     Those skilled in the art will also realize that, by utilizing conventional techniques, all or portions of the software&#39;s computer-executable instructions may be carried out by a dedicated electronic circuit such as a digital signal processor (“DSP”), programmable logic array (“PLA”), discrete circuits, and the like. The term “electronic apparatus” may include computing devices or consumer electronic devices comprising any software, firmware or the like, or electronic devices or circuits comprising no software, firmware or the like. 
     The term “firmware” typically refers to executable instructions, code or data maintained in an electronic device such as a ROM. The term “software” generally refers to executable instructions, code, data, applications, programs, or the like maintained in or on any form of computer-readable media. The term “computer-readable media” typically refers to system memory, storage devices and their associated media, communications media, and the like. 
     In view of the many possible embodiments to which the principles of the present invention and the forgoing examples may be applied, it should be recognized that the examples described herein are meant to be illustrative only and should not be taken as limiting the scope of the present invention. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and any equivalents thereto.