Patent Publication Number: US-9405481-B1

Title: Replicating using volume multiplexing with consistency group file

Description:
BACKGROUND 
     Computer data is vital to today&#39;s organizations and a significant part of protection against disasters is focused on data protection. As solid-state memory has advanced to the point where cost of memory has become a relatively insignificant factor, organizations can afford to operate with systems that store and process terabytes of data. 
     Conventional data protection systems include tape backup drives, for storing organizational production site data on a periodic basis. Another conventional data protection system uses data replication, by generating a copy of production site data of an organization on a secondary backup storage system, and updating the backup with changes. The backup storage system may be situated in the same physical location as the production storage system, or in a physically remote location. Data replication systems generally operate either at the application level, at the file system level, or at the data block level. 
     SUMMARY 
     In one aspect, a method includes replicating a first volume to a consistency group (CG) file on a backup device. The method also includes replicating a second volume to the CG file concurrently with the replicating of the first volume, the first and second volumes being in a consistency group. 
     In another aspect, an apparatus includes electronic hardware circuitry configured to replicate a first volume to a consistency group (CG) file on a backup device and replicate a second volume to the CG file concurrently with the replicating of the first volume, the first and second volumes being in a consistency group. 
     In a further aspect, an article includes a non-transitory computer-readable medium that stores computer-executable instructions. The instructions cause a machine to replicate a first volume to a consistency group (CG) file on a backup device and replicate a second volume to the CG file concurrently with the replicating of the first volume, the first and second volumes being in a consistency group. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an example of a data protection system. 
         FIG. 2  is an illustration of an example of a journal history of write transactions for a storage system. 
         FIG. 3  is a block diagram of an example of a system to initialize a backup snapshot. 
         FIG. 4  is a flowchart of an example of a process to initialize a backup snapshot. 
         FIG. 5  is a block diagram of an example of a system to initialize a backup snapshot. 
         FIG. 6  is a block diagram of an example of a system to synthesize new backup snapshots. 
         FIG. 7  is a flowchart of an example of a process to synthesize new backup snapshots. 
         FIG. 7A  is a flowchart of an example, of a process to generate a synthesis plan. 
         FIG. 8  is a block diagram of an example of a system to recover point-in-time data. 
         FIG. 9  is a flowchart of an example, of a process to recover point-in-time data. 
         FIG. 10  is a simplified diagram depicting data protection windows providing backup granularity. 
         FIG. 11  is a block diagram of another example of a data protection system using volume multiplexing. 
         FIG. 12  is a flowchart of an example of a process to perform snapshot replication to a backup device. 
         FIG. 13A  is a block diagram of an example of a CG file. 
         FIG. 13B  is a block diagram of an example of a copy of a CG file at a point-in-time. 
         FIG. 13C  is a block diagram of an example of a recovering a volume using the process of  FIG. 15 . 
         FIG. 13D  is a block diagram of an example of a CG file after a new volume has been added using a process of  FIG. 16 . 
         FIG. 13E  is a block diagram of an example of a CG file after a volume has been deleted using a process of  FIG. 17 . 
         FIG. 13F  is a block diagram of an example of a CG file after volume has been resized using a process of  FIG. 18 . 
         FIG. 14  is a flowchart of an example of a process to protect data using the data protection system of  FIG. 11 . 
         FIG. 15  is a flowchart of an example of a process to restore protected data from the data protection system of  FIG. 11 . 
         FIG. 16  is a flowchart of an example of a process to add a volume to a consistency group (CG) file in the data protection system of  FIG. 11 . 
         FIG. 17  is a flowchart of an example of a process to remove a volume from the CG file in the data protection system of  FIG. 11 . 
         FIG. 18  is a flowchart of an example of a process to resize a volume and resize the CG file in the data protection system of  FIG. 11 . 
         FIG. 19  is a simplified block diagram of an example of a computer on which any of the processes of  FIGS. 4, 7, 7A, 9, 12 and 14 to 18  may be implemented. 
     
    
    
     DETAILED DESCRIPTION 
     Described herein are techniques to perform continuous data protection using volume multiplexing. 
     The following definitions may be useful in understanding the specification and claims. 
     BACKUP SITE—a facility where replicated production site data is stored; the backup site may be located in a remote site or at the same location as the production site; a backup site may be a virtual or physical site. 
     BOOKMARK—a bookmark is metadata information stored in a replication journal which indicates a point in time. 
     CDP—Continuous Data Protection, a full replica of a volume or a set of volumes along with a journal which allows any point in time access, the CDP copy is at the same site, and maybe the same storage array of the production site. 
     DATA PROTECTION APPLIANCE (DPA)—a computer or a cluster of computers, or a set of processes that serve as a data protection appliance, responsible for data protection services including inter alia data replication of a storage system, and journaling of I/O requests issued by a host computer to the storage system. The DPA may be a physical device, a virtual device running, or may be a combination of a virtual and physical device. 
     DEDUPLICATED STORAGE SYSTEM—any storage system capable of storing deduplicated or space reduced data, and in some examples, is an EMC® DataDomain® system. Deduplicated data may also be any data that is processed to remove redundant data. 
     HOST—at least one computer or networks of computers that runs at least one data processing application that issues I/O requests to one or more storage systems; a host is an initiator with a SAN. 
     HOST DEVICE—an internal interface in a host, to a logical storage unit. 
     IMAGE—a copy of a logical storage unit at a specific point in time. 
     INITIATOR—a node in a SAN that issues I/O requests. 
     I/O REQUEST—an input/output request (sometimes referred to as an I/O or IO), which may be a read I/O request (sometimes referred to as a read request or a read) or a write I/O request (sometimes referred to as a write request or a write). 
     JOURNAL—a record of write transactions issued to a storage system; used to maintain a duplicate storage system, and to roll back the duplicate storage system to a previous point in time. 
     LOGICAL UNIT—a logical entity provided by a storage system for accessing data from the storage system. The logical disk may be a physical logical unit or a virtual logical unit. 
     LUN—a logical unit number for identifying a logical unit. 
     PHYSICAL LOGICAL UNIT—a physical entity, such as a disk or an array of disks, for storing data in storage locations that can be accessed by address. 
     PRODUCTION SITE—a facility where one or more host computers run data processing applications that write data to a storage system and read data from the storage system. 
     REMOTE ACKNOWLEDGEMENTS—an acknowledgement from remote DPA to the local DPA that data arrived at the remote DPA (either to the appliance or the journal). 
     SNAPSHOT—a snapshot is an image or differential representations of an image, i.e., the snapshot may have pointers to the original volume, and may point to log volumes for changed locations. Snapshots may be combined into a snapshot array, which may represent different images over a time period. 
     SPLITTER/PROTECTION AGENT—is an agent running either on a production host a switch or a storage array which can intercept Ms and split them to a DPA and to the storage array, fail Ms, redirect I/Os or do any other manipulation to the I/O; the splitter or protection agent may be used in both physical and virtual systems. The splitter may be in the I/O stack of a system and may be located in the hypervisor for virtual machines. In some examples, a splitter may be referred to as an Open Replicator Splitter (ORS). 
     SPLITTER ACKNOWLEDGEMENT—an acknowledgement from a DPA to the protection agent (splitter) that data has been received at the DPA; this may be achieved by an SCSI status command. 
     SAN—a storage area network of nodes that send and receive an I/O and other requests, each node in the network being an initiator or a target, or both an initiator and a target. 
     SOURCE SIDE—a transmitter of data within a data replication workflow, during normal operation a production site is the source side; and during data recovery a backup site is the source side, sometimes called a primary side. Source side may be a virtual or physical site. 
     STORAGE SYSTEM—a SAN entity that provides multiple logical units for access by multiple SAN initiators. 
     STREAMING—transmitting data in real time, from a source to a destination, as the data is read or generated. 
     SYNTHESIZE—generating a new file, for example, using pointers from existing files, without actually copying the referenced data. In one particular example, a new file representing a volume at a points-in-time may be generated using pointers to a file representing a previous point-in-time, as well pointers to journal representing changes to the volume. 
     TARGET—a node in a SAN that replies to I/O requests. 
     TARGET SIDE—a receiver of data within a data replication workflow; during normal operation a back site is the target side, and during data recovery a production site is the target side, sometimes called a secondary side. The target side may be a virtual or physical site. 
     THIN PROVISIONING—thin provisioning involves the allocation of physical storage when it is needed rather than allocating the entire physical storage in the beginning Thus, use of thin provisioning is known to improve storage utilization. 
     THIN LOGICAL UNIT—a thin logical unit is a logical unit that uses thin provisioning. 
     VIRTUAL LOGICAL UNIT—a virtual storage entity which is treated as a logical unit by virtual machines. 
     WAN—a wide area network that connects local networks and enables them to communicate with one another, such as the Internet. 
     A description of journaling and some techniques associated with journaling may be described in the patent titled “METHODS AND APPARATUS FOR OPTIMAL JOURNALING FOR CONTINUOUS DATA REPLICATION” and with U.S. Pat. No. 7,516,287, which is hereby incorporated by reference. 
     Referring to  FIG. 1 , a data protection system  100  includes two sites; Site I, which is a production site, and Site II, which is a backup site or replica site. Under normal operation the production site is the source side of system  100 , and the backup site is the target side of the system. The backup site is responsible for replicating production site data. Additionally, the backup site enables roll back of Site I data to an earlier pointing time, which may be used in the event of data corruption of a disaster, or alternatively in order to view or to access data from an earlier point in time. 
       FIG. 1  is an overview of a system for data replication of either physical or virtual logical units. Thus, one of ordinary skill in the art would appreciate that in a virtual environment a hypervisor, in one example, would consume logical units and generate a distributed file system on them such as VMFS generates files in the file system and expose the files as logical units to the virtual machines (each VMDK is seen as a SCSI device by virtual hosts). In another example, the hypervisor consumes a network based file system and exposes files in the NFS as SCSI devices to virtual hosts. 
     During normal operations, the direction of replicate data flow goes from source side to target side. It is possible, however, for a user to reverse the direction of replicate data flow, in which case Site I starts to behave as a target backup site, and Site II starts to behave as a source production site. Such change of replication direction is referred to as a “failover”. A failover may be performed in the event of a disaster at the production site, or for other reasons. In some data architectures, Site I or Site II behaves as a production site for a portion of stored data, and behaves simultaneously as a backup site for another portion of stored data. In some data architectures, a portion of stored data is replicated to a backup site, and another portion is not. 
     The production site and the backup site may be remote from one another, or they may both be situated at a common site, local to one another. Local data protection has the advantage of minimizing data lag between target and source, and remote data protection has the advantage is being robust in the event that a disaster occurs at the source side. 
     The source and target sides communicate via a wide area network (WAN)  128 , although other types of networks may be used. 
     Each side of system  100  includes three major components coupled via a storage area network (SAN); namely, (i) a storage system, (ii) a host computer, and (iii) a data protection appliance (DPA). Specifically with reference to  FIG. 1 , the source side SAN includes a source host computer  104 , a source storage system  108 , and a source DPA  112 . Similarly, the target side SAN includes a target host computer  116 , a target storage system  120 , and a target DPA  124 . As well, the protection agent (sometimes referred to as a splitter) may run on the host, or on the storage, or in the network or at a hypervisor level, and that DPAs are optional and DPA code may run on the storage array too, or the DPA  124  may run as a virtual machine. 
     Generally, a SAN includes one or more devices, referred to as “nodes”. A node in a SAN may be an “initiator” or a “target”, or both. An initiator node is a device that is able to initiate requests to one or more other devices; and a target node is a device that is able to reply to requests, such as SCSI commands, sent by an initiator node. A SAN may also include network switches, such as fiber channel switches. The communication links between each host computer and its corresponding storage system may be any appropriate medium suitable for data transfer, such as fiber communication channel links. 
     The host communicates with its corresponding storage system using small computer system interface (SCSI) commands. 
     System  100  includes source storage system  108  and target storage system  120 . Each storage system includes physical storage units for storing data, such as disks or arrays of disks. Typically, storage systems  108  and  120  are target nodes. In order to enable initiators to send requests to storage system  108 , storage system  108  exposes one or more logical units (LU) to which commands are issued. Thus, storage systems  108  and  120  are SAN entities that provide multiple logical units for access by multiple SAN initiators. 
     Logical units are a logical entity provided by a storage system, for accessing data stored in the storage system. The logical unit may be a physical logical unit or a virtual logical unit. A logical unit is identified by a unique logical unit number (LUN). Storage system  108  exposes a logical unit  136 , designated as LU A, and storage system  120  exposes a logical unit  156 , designated as LU B. 
     LU B is used for replicating LU A. As such, LU B is generated as a copy of LU A. In one example, LU B is configured so that its size is identical to the size of LU A. Thus, for LU A, storage system  120  serves as a backup for source side storage system  108 . Alternatively, as mentioned hereinabove, some logical units of storage system  120  may be used to back up logical units of storage system  108 , and other logical units of storage system  120  may be used for other purposes. Moreover, there is symmetric replication whereby some logical units of storage system  108  are used for replicating logical units of storage system  120 , and other logical units of storage system  120  are used for replicating other logical units of storage system  108 . 
     System  100  includes a source side host computer  104  and a target side host computer  116 . A host computer may be one computer, or a plurality of computers, or a network of distributed computers, each computer may include inter alia a conventional CPU, volatile and non-volatile memory, a data bus, an I/O interface, a display interface and a network interface. Generally a host computer runs at least one data processing application, such as a database application and an e-mail server. 
     Generally, an operating system of a host computer generates a host device for each logical unit exposed by a storage system in the host computer SAN. A host device is a logical entity in a host computer, through which a host computer may access a logical unit. Host device  104  identifies LU A and generates a corresponding host device  140 , designated as Device A, through which it can access LU A. Similarly, host computer  116  identifies LU B and generates a corresponding device  160 , designated as Device B. 
     In the course of continuous operation, host computer  104  is a SAN initiator that issues I/O requests (write/read operations) through host device  140  to LU A using, for example, SCSI commands. Such requests are generally transmitted to LU A with an address that includes a specific device identifier, an offset within the device, and a data size. Offsets are generally aligned to 512 byte blocks. The average size of a write operation issued by host computer  104  may be, for example, 10 kilobytes (KB); i.e., 20 blocks. For an I/O rate of 50 megabytes (MB) per second, this corresponds to approximately 5,000 write transactions per second. 
     System  100  includes two data protection appliances, a source side DPA  112  and a target side DPA  124 . A DPA performs various data protection services, such as data replication of a storage system, and journaling of I/O requests issued by a host computer to source side storage system data. As explained in detail herein, when acting as a target side DPA, a DPA may also enable roll back of data to an earlier point in time, and processing of rolled back data at the target site. Each DPA  112  and  124  is a computer that includes inter alia one or more conventional CPUs and internal memory. 
     For additional safety precaution, each DPA is a cluster of such computers. Use of a cluster ensures that if a DPA computer is down, then the DPA functionality switches over to another computer. The DPA computers within a DPA cluster communicate with one another using at least one communication link suitable for data transfer via fiber channel or IP based protocols, or such other transfer protocol. One computer from the DPA cluster serves as the DPA leader. The DPA cluster leader coordinates between the computers in the cluster, and may also perform other tasks that require coordination between the computers, such as load balancing. 
     In the architecture illustrated in  FIG. 1 , DPA  112  and DPA  124  are standalone devices integrated within a SAN. Alternatively, each of DPA  112  and DPA  124  may be integrated into storage system  108  and storage system  120 , respectively, or integrated into host computer  104  and host computer  116 , respectively. Both DPAs communicate with their respective host computers through communication lines such as fiber channels using, for example, SCSI commands or any other protocol. 
     DPAs  112  and  124  are configured to act as initiators in the SAN; i.e., they can issue I/O requests using, for example, SCSI commands, to access logical units on their respective storage systems. DPA  112  and DPA  124  are also configured with the necessary functionality to act as targets; i.e., to reply to I/O requests, such as SCSI commands, issued by other initiators in the SAN, including inter alia their respective host computers  104  and  116 . Being target nodes, DPA  112  and DPA  124  may dynamically expose or remove one or more logical units. 
     As described hereinabove, Site I and Site II may each behave simultaneously as a production site and a backup site for different logical units. As such, DPA  112  and DPA  124  may each behave as a source DPA for some logical units, and as a target DPA for other logical units, at the same time. 
     Host computer  104  and host computer  116  include protection agents  144  and  164 , respectively. Protection agents  144  and  164  intercept SCSI commands issued by their respective host computers, via host devices to logical units that are accessible to the host computers. A data protection agent may act on an intercepted SCSI commands issued to a logical unit, in one of the following ways: send the SCSI commands to its intended logical unit; redirect the SCSI command to another logical unit; split the SCSI command by sending it first to the respective DPA; after the DPA returns an acknowledgement, send the SCSI command to its intended logical unit; fail a SCSI command by returning an error return code; and delay a SCSI command by not returning an acknowledgement to the respective host computer. 
     A protection agent may handle different SCSI commands, differently, according to the type of the command. For example, a SCSI command inquiring about the size of a certain logical unit may be sent directly to that logical unit, while a SCSI write command may be split and sent first to a DPA associated with the agent. A protection agent may also change its behavior for handling SCSI commands, for example as a result of an instruction received from the DPA. 
     Specifically, the behavior of a protection agent for a certain host device generally corresponds to the behavior of its associated DPA with respect to the logical unit of the host device. When a DPA behaves as a source site DPA for a certain logical unit, then during normal course of operation, the associated protection agent splits I/O requests issued by a host computer to the host device corresponding to that logical unit. Similarly, when a DPA behaves as a target device for a certain logical unit, then during normal course of operation, the associated protection agent fails I/O requests issued by host computer to the host device corresponding to that logical unit. 
     Communication between protection agents and their respective DPAs may use any protocol suitable for data transfer within a SAN, such as fiber channel, or SCSI over fiber channel. The communication may be direct, or via a logical unit exposed by the DPA. Protection agents communicate with their respective DPAs by sending SCSI commands over fiber channel. 
     Protection agents  144  and  164  are drivers located in their respective host computers  104  and  116 . Alternatively, a protection agent may also be located in a fiber channel switch, or in any other device situated in a data path between a host computer and a storage system or on the storage system itself. In a virtualized environment, the protection agent may run at the hypervisor layer or in a virtual machine providing a virtualization layer. 
     What follows is a detailed description of system behavior under normal production mode, and under recovery mode. 
     In production mode DPA  112  acts as a source site DPA for LU A. Thus, protection agent  144  is configured to act as a source side protection agent; i.e., as a splitter for host device A. Specifically, protection agent  144  replicates SCSI I/O write requests. A replicated SCSI I/O write request is sent to DPA  112 . After receiving an acknowledgement from DPA  124 , protection agent  144  then sends the SCSI I/O write request to LU A. After receiving a second acknowledgement from storage system  108  host computer  104  acknowledges that an I/O command complete. 
     When DPA  112  receives a replicated SCSI write request from data protection agent  144 , DPA  112  transmits certain I/O information characterizing the write request, packaged as a “write transaction”, over WAN  128  to DPA  124  on the target side, for journaling and for incorporation within target storage system  120 . 
     DPA  112  may send its write transactions to DPA  124  using a variety of modes of transmission, including inter alia (i) a synchronous mode, (ii) an asynchronous mode, and (iii) a snapshot mode. In synchronous mode, DPA  112  sends each write transaction to DPA  124 , receives back an acknowledgement from DPA  124 , and in turns sends an acknowledgement back to protection agent  144 . Protection agent  144  waits until receipt of such acknowledgement before sending the SCSI write request to LU A. 
     In asynchronous mode, DPA  112  sends an acknowledgement to protection agent  144  upon receipt of each I/O request, before receiving an acknowledgement back from DPA  124 . 
     In snapshot mode, DPA  112  receives several I/O requests and combines them into an aggregate “snapshot” of all write activity performed in the multiple I/O requests, and sends the snapshot to DPA  124 , for journaling and for incorporation in target storage system  120 . In snapshot mode DPA  112  also sends an acknowledgement to protection agent  144  upon receipt of each I/O request, before receiving an acknowledgement back from DPA  124 . 
     For the sake of clarity, the ensuing discussion assumes that information is transmitted at write-by-write granularity. 
     While in production mode, DPA  124  receives replicated data of LU A from DPA  112 , and performs journaling and writing to storage system  120 . When applying write operations to storage system  120 , DPA  124  acts as an initiator, and sends SCSI commands to LU B. 
     During a recovery mode, DPA  124  undoes the write transactions in the journal, so as to restore storage system  120  to the state it was at, at an earlier time. 
     As described hereinabove, LU B is used as a backup of LU A. As such, during normal production mode, while data written to LU A by host computer  104  is replicated from LU A to LU B, host computer  116  should not be sending I/O requests to LU B. To prevent such I/O requests from being sent, protection agent  164  acts as a target site protection agent for host Device B and fails I/O requests sent from host computer  116  to LU B through host Device B. 
     Target storage system  120  exposes a logical unit  176 , referred to as a “journal LU”, for maintaining a history of write transactions made to LU B, referred to as a “journal”. Alternatively, journal LU  176  may be striped over several logical units, or may reside within all of or a portion of another logical unit. DPA  124  includes a journal processor  180  for managing the journal. 
     Journal processor  180  functions generally to manage the journal entries of LU B. Specifically, journal processor  180  enters write transactions received by DPA  124  from DPA  112  into the journal, by writing them into the journal LU, reads the undo information for the transaction from LU B. updates the journal entries in the journal LU with undo information, applies the journal transactions to LU B, and removes already-applied transactions from the journal. 
     Referring to  FIG. 2 , which is an illustration of a write transaction  200  for a journal. The journal may be used to provide an adaptor for access to storage  120  at the state it was in at any specified point in time. Since the journal includes the “undo” information necessary to roll back storage system  120 , data that was stored in specific memory locations at the specified point in time may be obtained by undoing write transactions that occurred subsequent to such point in time. 
     Write transaction  200  generally includes the following fields: one or more identifiers; a time stamp, which is the date &amp; time at which the transaction was received by source side DPA  112 ; a write size, which is the size of the data block; a location in journal LU  176  where the data is entered; a location in LU B where the data is to be written; and the data itself. 
     Write transaction  200  is transmitted from source side DPA  112  to target side DPA  124 . As shown in  FIG. 2 , DPA  124  records the write transaction  200  in the journal that includes four streams. A first stream, referred to as a DO stream, includes new data for writing in LU B. A second stream, referred to as an DO METADATA stream, includes metadata for the write transaction, such as an identifier, a date &amp; time, a write size, a beginning address in LU B for writing the new data in, and a pointer to the offset in the DO stream where the corresponding data is located. Similarly, a third stream, referred to as an UNDO stream, includes old data that was overwritten in LU B; and a fourth stream, referred to as an UNDO METADATA, include an identifier, a date &amp; time, a write size, a beginning address in LU B where data was to be overwritten, and a pointer to the offset in the UNDO stream where the corresponding old data is located. 
     In practice each of the four streams holds a plurality of write transaction data. As write transactions are received dynamically by target DPA  124 , they are recorded at the end of the DO stream and the end of the DO METADATA stream, prior to committing the transaction. During transaction application, when the various write transactions are applied to LU B, prior to writing the new DO data into addresses within the storage system, the older data currently located in such addresses is recorded into the UNDO stream. In some examples, the metadata stream (e.g., UNDO METADATA stream or the DO METADATA stream) and the data stream (e.g., UNDO stream or DO stream) may be kept in a single stream each (i.e., one UNDO data and UNDO METADATA stream and one DO data and DO METADATA stream) by interleaving the metadata into the data stream. 
       FIGS. 3 to 5  depict systems and processes for initializing a backup snapshot on deduplicated storage consistent. Before deduplicated storage can provide continuous backup protection, it may be necessary to generate an initial backup snapshot of the source storage system. This initial backup snapshot may represent the earliest point-in-time backup that may be restored. As changes are made to the source storage system, journal files and/or new backups may be updated and/or synthesized to provide continuous protection. In some examples, the initial backup snapshot may be generated by streaming I/Os from a storage system scan to a data protection appliance, or by taking an initial snapshot of the storage system and transmitting the entire snapshot to deduplicated storage. 
       FIG. 3  depicts a system for generating an initial backup snapshot by scanning a source storage system and streaming I/Os to the deduplicated storage. Data protection application  300  may include journal processor  302 , and may be in communication with deduplicated storage  304 . In one example, deduplicated storage  304  may be target side storage residing at a backup site. Data protection appliance  300  may be similar to data protection appliance  112  and/or  124 , and may be responsible for streaming I/Os to deduplicated storage  304 . 
     In one example, a source storage system may be scanned and individual offsets may be streamed to data protection appliance  300 . The offsets streamed from the scanned system may be referred to as initialization I/Os, and may be streamed sequentially to data protection appliance  300 . For example, the scanned system may include offsets 0, 1, 2, and 3, comprising data A, B, C, and D. The initial scan may start at the beginning of the system, and transmit offset 0, followed by offset 1, and so forth. 
     As data protection appliance  300  receives the initialization I/Os, journal processor  302  may identify the offset data and metadata, and may stream the I/Os to metadata journal  306  and/or data journal  308  residing on deduplicated storage  304 . Data journal  308  may include data stored within an offset, and metadata  306  may include metadata associated with that offset. Metadata could include, for example, an offset identifier, size, write time, and device ID. These journals may then be used to synthesize a backup snapshot on deduplicated storage  304 , as described herein. 
     In some examples, a scanned storage system may operate in a live environment. As a result, applications may be writing to the storage concurrently with the scan process. If an application writes to a location that has already been streamed, the journal files and ultimately the synthesized snapshot may be out of date. To address this issue, application I/Os may be streamed concurrently with the initialization I/Os if the application I/Os are to an offset that has already been scanned. For example, consider Table 1: 
     
       
         
           
               
               
               
            
               
                   
               
               
                   
                 Time 
                   
               
            
           
           
               
               
               
               
               
            
               
                 Offset 
                 t0 
                 t1 
                 t2 
                 t3 
               
               
                   
               
               
                 0 
                 A 
                   
                   
                 A′ 
               
               
                 1 
                 B 
                 B′ 
                   
                   
               
               
                 2 
                 C 
                   
                   
                   
               
               
                 3 
                 D 
                   
                 D′ 
               
               
                   
               
            
           
         
       
     
     Table 1 depicts four different offsets, denoted as 0, 1, 2, and 3, and four times, t0, t1, t2, and t3. Letters A, B, C, and D may represent the data stored at the offsets. Time t0 may represent the offsets as they exist when the scan begins. These offsets may be streamed to data protection appliance  300  sequentially from 0 to 3. At time t1, however, the data at offset 1 is modified by an application from B to B′. Similarly, at t2 the data at offset 3 changes from D to D′, and at t3 the data at offset 0 changes from A to A′. If the scan transmits the data at offset 1 before t1, B′ may be missed since the change occurred after offset 1 was scanned and B was transmitted. Similarly, if the scan has not reached offset 3 before t2, only D′ will be transmitted since D no longer exists. It may therefore be beneficial to transmit application I/Os to data protection appliance  300  if those I/Os write to an offset that has already been scanned. If the offset has not been scanned, it may not be necessary to transmit the application I/Os because the change will be transmitted when the scan reaches that offset. 
     Referring back to  FIG. 3  and with continued reference to Table 1, offset metadata journal entries  310  and offset data journal entries  312  depict the state of metadata journal  306  and data journal  308  after the initial scan is complete. While there are only four offsets on the scanned storage system, there are six entries in the journal because the data in offset 0 and 1 was modified by an application after they were scanned. They each therefore have two entries: B and B′. Segment D was modified after the scan began, but before it was reached. Segment D therefore only has one entry: D′. 
     Metadata journal entries  310  and data journal entries  312  may include all of the data necessary to synthesize a backup snapshot of the scanned storage system. Data journal entries  312  may include the actual data from the storage system: A, B, B′ C, A′ and D′. Note that data D is not in the data journal  308  since it was modified on the storage system before its offset was scanned and transmitted. Metadata journal entries  310  may include metadata about the offsets. For example, metadata journal entries  310  may include an offset identifier, offset length, and write time, and volume/device ID. In the present example, metadata journal entries may include the entries shown in Table 2: 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Offset/Time 
                 Volume 
                 Offset 
                 Time 
               
               
                   
                   
               
             
            
               
                   
                 0 
                 A 
                 0 
                 t0 
               
               
                   
                 1 
                 A 
                  8 kb 
                 t0 
               
               
                   
                 2 
                 A 
                  8 kb 
                 t1 
               
               
                   
                 3 
                 A 
                 16 kb 
                 t0 
               
               
                   
                 4 
                 A 
                 0 
                 t3 
               
               
                   
                 5 
                 A 
                 24 kb 
                 t2 
               
               
                   
                   
               
            
           
         
       
     
     Table 2&#39;s metadata entries may correspond to the states shown in Table 1. The offset at location 0 may be offset 0, the offset at 8 kb may be offset 1, the offset at 16 kb may be offset 2, and the offset at 24 kb may be offset 3. The subscript of each journal entries  310  also identifies the offset associated with that metadata entry. 
     Deduplicated storage may use metadata journal  306  and data journal  308  to synthesize initial backup snapshot  314 . First, metadata journal  306  may be queried to identify the most recent data associated with each offset. Next, the data may be retrieved from journal data file  308  and synthesized into backup snapshot  314 . In some examples, synthesizing the backup snapshot may include generating and/or copying pointers rather than copying entire data blocks. This could be, for example, using a product such as EMC® Data Domain® Boost™ 
     For example, once the initial scan is complete, data journal  308  includes data A, B, B′, C, A′, and D′. A′ and B′ are the result of application I/Os occurring during the scan process, and therefore represent the present state of offsets 0 and 1. To generate backup snapshot  314 , deduplicated storage may therefore retrieve A′, B′, C, and D′ from the data journal  308  and synthesize them together. 
     Once initial backup snapshot  314  is synthesized, journal entries  310  and  312  may no longer be needed. In some examples, they may be removed from deduplicated storage  304  in order to conserve space. Alternatively, they may remain in the journals. 
     The systems and processes described in reference to  FIG. 3  enable a system to generate an initial backup snapshot. Once the initial snapshot is generated, additional processes may enable continuous data protection and point-in-time recovery. 
     Referring to  FIG. 4 , an example of a process to generate an initial backup snapshot is a process  400 , which includes processing blocks  401 ,  402 ,  404 ,  406 ,  408 ,  410 ,  412 ,  414  and  416 . At block  401 , sequential initialization I/Os are received from a scanned storage volume. These I/Os could be, for example, received at a data protection appliance, such as data protection appliance  300 . In some examples, the initialization I/Os are read from the scanned storage volume by the data protection appliance. 
     At block  402 , the initialization I/Os are streamed to a deduplicated storage. In an example, the deduplicated storage may be substantially similar to deduplicated storage  304 . In some examples, the initialization I/Os are streamed to a data journal using a data stream, and to a metadata journal using a metadata stream. Each stream may be a file in the deduplicated storage. Additionally or alternatively, writes to the journal files may be performed through the EMC® Data Domain® Boost™ API or any other API. 
     At block  404 , the initialization I/Os may be written to a journal on the deduplicated storage. This journal may be, for example, similar to metadata journal  306  and/or data journal  308 . In an example, these journals may be in the same journal files. Alternatively, these may be separate files on the deduplicated storage system. 
     At block  406 , application I/Os comprising writes to offsets on the scanned storage volume may be received. These application I/Os may also be received at a data protection appliance, such as data protection appliance  300 . 
     At block  408 , an offset associated with a specific application I/O is identified, and at block  410  it is determined whether the offset has already been streamed to the deduplicated storage. 
     This determination could be made on data protection appliance  300  using journal processor  302 . If the offset has already been streamed, it must have already been scanned and included in an initialization I/O. If the offset has not been streamed, the storage volume scan may not have reached the offset on the storage volume. 
     At block  412 , the application I/O is streamed to the deduplicated storage if its offset was included in a previously streamed initialization I/O. In an example, the application I/O is only streamed when its offset was included a previously streamed initialization I/O. Streaming the application I/O when its offset was included in a previous initialization I/O ensures that writes to the scanned volume are not missed during the initialization processes. In some examples, the application I/Os are streamed to a data journal using a data stream, and to a metadata journal using a metadata stream. 
     In an example, application Ms are not streamed if they comprise writes to an offset that has not yet been scanned and streamed in an initialization I/O. This is because the data generated by the write will be included in the initialization I/O once the scan reaches that offset. This may reduce traffic between the data protection appliance and the deduplicated storage, and may reduce the workload on the deduplicated because the data will only be processed once. 
     At block  414 , the application I/O is written to the journal. This journal may be the same journal as the initialization I/Os, or it may be a separate journal. In an example, the journal is data journal  308  and/or metadata journal  306 . 
     At block  416 , a backup snapshot is synthesized from the initialization I/Os and the application I/Os. This snapshot may be substantially similar to snapshot  314 . In an example, the snapshot is synthesized by generating data pointers in a new file on the deduplicated storage. Additionally or alternatively, the pointers may be copied from the data journal. These pointers may point to the data referenced and/or included in the journal. Synthesizing the snapshot using pointers may improve performance, as the data may not need to be replicated. 
       FIG. 5  depicts an additional or alternative example for initializing a backup snapshot. The system shown in  FIG. 5  may include data protection appliance  500 , journal processor  502 , and deduplicated storage  504 . These elements may be substantially similar to those described in reference to  FIG. 3 . 
     Data protection appliance  500  may take a snapshot of a storage system and transmit that snapshot to deduplicated storage  504  for storage as a file. In an example, this is different than streaming initialization I/Os and synthesizing a snapshot from journal files. 
     Rather than generating the snapshot on the deduplicated storage, the backup snapshot is generated using the data protection appliance and transmitted to deduplicated storage to be stored as backup snapshot  514 . 
     In an example, journal processor  502  may stream application I/Os to deduplicated storage, and those application Ms may be stored in metadata journal  506  and data journal  508 . Like the journals of  FIG. 3 , metadata journal  506  may include metadata journal entries  510 , and data journal  508  may include data journal entries  512 . These journals may be used to synthesize a second backup snapshot or enable point-in-time recovery, as described below. 
     The systems and processes described in reference to  FIGS. 3 to 5  enable a system to generate an initial backup snapshot. Once the initial snapshot is generated, additional processes may enable continuous data protection and point-in-time recovery. 
     Referring to  FIG. 6 , a system and process for maintaining backups using continuous data replication is described. As datasets increase in size, backing them up to remote or local backup devices becomes increasingly costly and complex. Additionally, traditional backup processes may not allow point-in-time recovery since the backups occur on a periodic, rather than continuous, basis. The methods and systems described herein provide continuous backup protection as writes are made to a source device, thereby reducing backup cost and complexity, and may allowing point-in-time recovery for backed up files. 
     The system of  FIG. 6  includes a data protection appliance  600 , a journal processor  602 , and a deduplicated storage  604 . These elements may be substantially similar to those described in reference to  FIG. 3 . Deduplicated storage  604  may include a backup snapshot  614 , a metadata journal file  606 , and a data journal file  608 . In one example, backup snapshot file  614  is synthesized in a manner substantially similar to backup snapshot  314 , and may be generated using metadata journal entries  610  and data journal entries  612 . 
     As users, applications, and other processes access and use the source storage system, data on that system may change and/or new data may be generated. As a result, initial backup snapshot  614  may become stale. If the source storage system should fail, there is a chance that any new or modified data may be lost. To address this concern, data protection appliance  600  may receive and stream application I/Os to deduplicated storage system  604  on a continuous basis, even after initial backup snapshot  614  is synthesized. Streaming the application I/Os allows the backups on deduplicated storage  604  to remain up-to-date, without needing to perform additional backups of large datasets. This may reduce network traffic, reduce workloads, and conserve space on deduplicated storage  604 . 
     For example, new metadata entries  611  and new data journal entries  613  represent I/Os made after initial backup snapshot  614  was synthesized. These entries may be written to metadata journal  606  and data journal  608 , as shown in  FIG. 6 , or they may be written to separate journal files. In  FIG. 6 , data A′ and C were modified on the source storage device, and the journal entries therefore include A″ and C′. 
     Periodically, new backup snapshots may be synthesized from a previous backup snapshot and new journal entries. For example, second backup snapshot  616  may be synthesized from initial backup snapshot  614 , new metadata journal entries  611 , and new data journal entries  613 . Second backup snapshot  616  may be used to restore source storage system up to the point-in-time the last journal entry was received. That is, backup snapshot  616  represents a backup of the source storage system at a later timestamp than initial backup snapshot  614 . 
     In one example, synthesizing second backup journal entry  616  may be substantially similar to synthesizing the initial backup snapshot  614 . Rather than synthesizing all of the data from data journal  608 , however, unchanged data may be synthesized from initial backup snapshot  614 . In one example, this synthesis may include copying and/or generating a data pointer. For example, in  FIG. 6  the solid arrows between initial backup snapshot  614  and second backup snapshot  616  represent unchanged data that is common between the two. In this case, only B′ and D′ remain unchanged. The dashed arrows represent new or changed data that needs to be synthesized into second backup snapshot  616 . In  FIG. 6 , A′ is changed to A″, C is change to C′. Synthesizing the data into second backup snapshot  616  therefore results in A″, B′, C′, D′. 
     Additionally or alternatively, second backup snapshot  616  may be synthesized entirely from journal entries. Rather than synthesizing unchanged data from initial backup  614 , deduplicated storage  604  may retrieve the unchanged data from data journal entries  612 . For example, B′ and D′ may be synthesized from data journal entries  612  rather than from initial backup snapshot  614 . 
     Additional backup snapshots, such as second backup snapshot  616 , may be generated periodically or on demand. For example, a user policy may specify that new snapshots should be generated every week. Additionally or alternatively, a user may be preparing to perform some risky operations on the source storage system, and may demand that a snapshot be generated in case something goes wrong. These policies may be maintained and applied using data protection appliance  600 , deduplicated storage  604 , and/or an external system. 
     Referring to  FIG. 7 , an example of a process to maintain backup snapshots using continuous data replication is a process  700 , which includes processing blocks  701 ,  702 ,  704 ,  706 ,  708  and  710 . At block  701 , an initial snapshot of a source storage system may be generated. This initial snapshot may be substantially similar to initial backup snapshot  614 , and may be generated using any one of the processes described in reference to  FIGS. 3 to 5 . Additionally or alternatively, the initial snapshot may be any previously generated snapshot. For example, the initial snapshot may be similar to second backup snapshot  616 , and may be used in conjunction with journal files to generate a third backup snapshot. 
     At block  702 , application I/Os comprising writes to the source storage system may be received. These writes may update existing data or generate new data. In some examples, the application I/Os may be received by a data protection appliance, such as data protection appliance  600 . 
     At block  704 , the application I/Os may be written to a journal file. This journal file may be substantially similar to metadata journal file  606  and/or data journal file  608 . In some examples, the application I/Os may be written to one or more existing journals. Alternatively, application I/Os arriving after a snapshot is synthesized may be written to their own unique journals. This may be beneficial, for example, when maintaining different levels of backup granularity, as described below. 
     In some examples, the application I/Os are sequentially written to the journal as they are received. For example, if application I/Os arrive in order B, C, A, their corresponding entries in the journal will also be B, C, A. 
     At block  706 , a second snapshot may be synthesized from the initial backup snapshot and the journal. The second snapshot may be substantially similar to second backup snapshot  616 , and the synthesis process may be similar to that depicted by the solid and dashed lines. In some examples, the second snapshot may be synthesized entirely from journal files rather than use the initial backup snapshot. 
     During and/or after the synthesis process, additional application I/Os may be received at block  708 . These application I/Os could be used, for example, to generate the third backup snapshot in the future, and may be processed in a manner similar to all the other application I/Os described herein. 
     At block  710  the additional application I/Os may be written to a journal file. They may be written to the same journal as the previous I/Os, or they may be written to a new journal file. 
     Referring to  FIG. 7A , an example of a process to synthesize snapshots used for continuous data replication is a process  712 , which includes processing blocks  713 ,  714 ,  716  and  718 . At block  712 , a metadata journal may be read. This metadata journal could be, for example, metadata journal file  606 . In some examples, the metadata journal may be read using a journal processor on a data protection appliance. Additionally or alternatively, the read operation may be local to the deduplicated storage device. 
     At block  714 , the latest I/Os for each offset may be identified. For example, metadata journal file  606  includes journal entries  610  and  611 . The latest entry for offset 0 is A″, 1 is B′, 2 is C′, and 3 is D′. In some examples, journal entries  610  and  611  may be written to different journals. In such some examples, the only I/Os identified would be A″ and C′ since we are synthesizing a snapshot from initial backup snapshot  614 . 
     At block  716 , a synthesis plan may be generated. This plan may identify where each I/O should be synthesized from. For example, the synthesis plan may only identify A″ and C′ for synthesis from data journal  608 . The B′ and D′, in contrast, may be obtained from initial backup snapshot  614  since they have not changed. 
     At block  718 , the backup snapshot may be synthesized. This backup snapshot could be, for example, substantially similar to backup snapshot  616 . 
     The system and processes described herein may enable additional backup snapshots to be synthesized from journal entries and existing snapshots. In some examples, the journal entries may be application I/Os which are continuously streamed to a data protection appliance. While these snapshots may provide additional data protection, they may only allow data that exists in the snapshots to be recovered. Combining snapshots and journal files may, however, allow any point-in-time recovery. 
     When datasets are backed-up on a periodic rather than continuous basis, data recovery may only be available for specific time intervals. For example, if a dataset is backed up at the end of every business day, the only data that is available for recovery is the data as it exists at the end of the day. Continuous backups, however, may allow recovery of data at any, or nearly any, point-in-time. By transmitting application I/Os to a backup location as they occur, an interim snapshot may be synthesized between scheduled snapshots and data may be recovered. 
       FIGS. 8 and 9  depict a system and process to synthesize an interim snapshot for point-in-time recovery. In one example, the system may include data protection appliance  800 , journal processor  802 , and deduplicated storage  804 . The system may also include metadata journal file  806 , comprising metadata journal entries  810  and  811 , and data journal file  808 , comprising data journal entries  812  and  813 . 
     Data protection appliance  800  may receive application I/Os as they are made to a source storage system. In some examples, journal processor  802  may write those I/Os to metadata journal file  806  and data journal file  808 . Initialization journal entries  810  and  812  may be used to synthesize initial backup snapshot  814 . Metadata entries  811  and data journal file entries  813  may be application I/Os made to the source storage volume after or while initial backup snapshot  814  was synthesized. These elements may be substantially similar to those described in reference to  FIG. 6 . 
     In one example, metadata journal entries  811  and data journal entries  813  may be used to synthesize interim snapshot  816 . Interim snapshot  816  may then be used as a source for point-in-time recovery. For example, application I/Os A″ and C′ may be streamed to deduplicated storage as they are made to the source storage system. A user may then decide they wish recover data from the point-in-time immediately after application I/O A″ was streamed. When the user&#39;s request arrives, the most recent snapshot may be initial backup snapshot  814 , which does not include A″ or C′. To respond to the user&#39;s request, deduplicated storage  804  may synthesize interim snapshot  816 . This snapshot may include unchanged data from initial backup snapshot  814 , as shown by the solid black arrows, and application I/O A″ synthesized from data journal file  808 , as shown by the dashed arrow. Note that interim snapshot  816  does not include C′. This is because the user requested data recovery at a point-in-time before C′ may made. 
     In one example, the data from interim snapshot  816  may be transmitted back to the source storage system and recovered. Additionally or alternatively, it may be exposed to a host as LUN, as described in reference to  FIGS. 12 and 13 . Interim snapshot  816  may be deleted after recovery, or may be retained. In some examples, if interim snapshot  816  is generated at a point-in-time sufficiently close to a scheduled synthesis time, the scheduled synthesis may be cancelled and interim snapshot  816  may be treated as second backup snapshot  616 . 
     Referring to  FIG. 9 , an example of a process to perform recovery for a point-in-time is a process  900 , which includes processing blocks  901 ,  902 ,  904 ,  906  and  908 . At block  901 , a request to recover some data is received. This request could be, for example, received at data protection appliance  800  and/or deduplicated data storage  804 . In one example, the request may specify a file representing a LUN to recover, or it may be a request to recover an entire system. Additionally or alternatively, the request may specify a point-in-time for the recovery. The point-in-time may be a date, event, or any other mechanism to identify a specific time. In some examples, the point-in-time may be between snapshots. 
     At block  902 , a snapshot nearest the point-in-time may be identified. The snapshot could be, for example, initial backup snapshot  814 . 
     At block  906 , a recovery snapshot may be synthesized. This recovery snapshot could be, for example, substantially similar to interim snapshot  816 . If the recovery snapshot is synthesized using a snapshot from an earlier point-in-time, I/Os stored in a journal file may be applied to synthesize the recovery snapshot. 
     At block  908  the recovery snapshot may be provided in response to the request. For example, the recovery snapshot may be exposed as a LUN and mounted on a host computer, or exposed as a network file system share. Additionally or alternatively, the recovery snapshot may be transmitted back to the source storage system. In some examples, only a portion of the snapshot, such as a specific file, may be provided. 
     Combining backup snapshots, journals, and continuous data replication may provide point-in-time recovery capabilities. As more data is written to and/or modified on a source storage system, however, the number of journals and snapshots may increase. In some examples, data protection windows may be used to manage this data growth. 
     As the number of snapshots and journals on the deduplicated storage grows, more space may be required. Deleting snapshots and journals may result in important information being lost, and adding to space to the deduplicated storage may be expensive. To address these concerns, backup windows and policies may be defined. Backup windows may be defined intervals designating which snapshot and journals should be stored, and for how long. 
       FIG. 10  depicts a system and process to define backup granularity using data protection windows.  FIG. 10  shows seventeen snapshot files, labeled S 1  through S 17 , stored on a deduplicated storage device. These snapshots may be generated and maintained in a manner substantially similar to that described above. The deduplicated storage device may also include six journal files, labeled J 1  through J 6 , which may be used to synthesize new snapshots or perform point-in-time recovery. 
       FIG. 10  also includes three data protection windows: short-term protection window  1000 , mid-term protection window  1002 , and long term protection window  1004 . Each of these protection windows may have an associated policy specifying actions to take on any snapshot and/or journal file within the protection window. For example, one policy may be “delete all journals within this protection window.” While the examples described herein address deletion and/or retention policies, any other policy which may be applied to the journals and/or snapshots is consistent with this disclosure. 
     Short-term protection window  1000  may be defined to protect both snapshots and journal files allowing for point-in-time recovery. This window may be particularly beneficial for snapshots that were generated recently and/or were generated on demand by a user. On demand generation may signify that the snapshot is more important than a scheduled snapshot because a user must go out of their way to generate it. Further, it may be more likely that a user needs to recover data which was modified or generated recently. 
     Mid-term protection window  1002  may include only snapshot files. As time progresses and journal files move from short-term protection window  1000  into mid-term protection window  1002 , they may be deleted. While deleting journal files may prevent most point-in-time recovery, the snapshots may be maintained in mid-term protection window. As a result, some level of point-in-time recovery is preserved. Specifically, any data included in one of the maintained snapshots may be recovered. Mid-term protection window therefore balances storage needs with recovery needs. 
     As snapshots move from mid-term protection  1002  window into long-term protection window  1004 , certain snapshots may be deleted. Point-in-time recovery may be less important for long-term backups because of their age. The deleted snapshots may be chosen based on a policy, such as size or a user assigned priority. Additionally or alternatively, they may be arbitrarily chosen (for example, only retaining every fifth snapshot). 
     In some examples, data protection windows may be defined and maintained using a data protection appliance, a deduplicated storage device, and/or an external system. For example, if the data protection window is defined using a deduplicated storage device, that device may delete the journals and/or snapshots as the move from one data protection window into another. In some examples, the data protection windows may change dynamically based on available space on the deduplicated storage device. For example, if there is a large amount of available space the short-term protection window may be very large, and/or the mid-term and long-term protection windows may not exist. Similarly, if there is not much available space the long-term protection window may be very long. In further examples the short term protection may not exist at all and the system may use snapshot shipping in order to generate mid- and long-term snapshots on the deduplicated storage device. 
     In some examples, a backup system has a limited amount of resources and the number of files or stream the system can manage is limited. In such examples, keeping a file open for each replicated volume is problematic, and thus multiplexing multiple volumes into one file may be required. 
     Referring to  FIG. 11 , an example of a data protection system that includes volume multiplexing is a data protection system  1100 . The system  1100  includes a DPA  1104 , a storage array  1106 , a backup storage device  1116  (e.g., a de-duplication device). The storage array  1106  includes a first storage volume  1108   a , a second storage volume  1108   b  and a third storage volume  1108   c.    
     The backup storage  1116  includes a consistency group (CG) file  1122 , which is a single, concatenated, file that holds data for LUNs (volumes) in a given consistency group. For example, the CG file  1122  includes a replica of the first, second and third storage  1108   a - 1108   c . The volumes  1108   a - 1108   c  are replicated to the CG file concurrently. Using this approach, resource requirements are reduced to a single write-stream per CG (rather than per replicated LUN (volume)) to the backup device  1116 , which gives an order-of-magnitude reduction in the requirements. That is, volume multiplexing provides a better approach than copying a file for each volume, which would require a large number of open files when replicating, as each source LUN maps to a file. For example, thousands of LUNs being replicated concurrently would lead to thousands of write-streams to the backup device  1116 , which typically exceeds the resource requirements of backup devices. 
     The backup storage  1116  may also include point-in-time (PIT) copies of the CG file  1122  (e.g., a first copy of the CG file  1132 , a second copy of the CG file  1133  and a third copy of the CG file  1134 ). In one example, a PIT copy is generated periodically. 
     Each of the PIT copies  1132 ,  1133 ,  1134  includes metadata (e.g., the first copy of CG file  1132  includes metadata  1144 , the second copy of CG file  1133  includes metadata  1145  and the third copy of CG file  1134  includes metadata  1146 ). In one example, each metadata  1144 ,  1145 ,  1146  includes a timestamp when the copy of the CG file was generated, a list of volumes that are included in the copy of the CG file and the sizes of the volumes. 
     As further described herein the copies  1132 ,  1133 ,  1134  may be used to extract copies of the first, second and third volumes  1108   a - 1108   c  (e.g., from the first copy of the CG File  1132 , a copy of the first storage volume  1108   a  (i.e., volume  1142   a  may be extracted) as well as volumes  1142   b ,  1142   c , which are copies of volume  1108   b ,  1108   c  respectively. 
     Referring to  FIG. 12 , a process  1200  is an example of a process to perform snapshot replication to a backup device (e.g., the backup storage  1116 ). Process  1200  generates the first snapshot of a set of volumes ( 1202 ), sends the first snapshot to the backup device by writing the data to the CG file ( 1206 ) and generates a snapshot of the CG file (e.g., first copy of the CG file  1132 ) ( 1208 ). Process  1200  generates the next snapshot of the volumes ( 1210 ) and sends the differences between the previous and latest snapshot to the CG file ( 1212 ). Process  1200  generates a snapshot of the CG file (e.g., a second copy of the CG file  1133 ) ( 1214 ). 
     Referring to  FIG. 13A , an example of the CG file  1122  is the CG file  1122 ′. The CG file  1122  is a multiplexed file that includes concatenated versions of the volumes  1108   a - 1108   c . In this example, the CG file  1122 ′ includes replica of a first storage volume  1108   a ′, a replica of the second storage volume  1108   b ′ and a replica of third storage volume  1108   c ′. In this example, if the volumes  1108   a - 1108   c  have sizes of 1 GB, 2 GB and 3 GB respectively then the CG file  1122 ′ will be 6 GB in size and the offset from 0 to 1 GB will be the first replica of the first volume  1108 ′, the offset from 1 GB to 3 GB will be the replica of the second volume  1108   b ′ and the offset from 3 GB to 6 GB will be the replica of the third volume  1108   c′.    
     Referring to  FIG. 13B , an example of a first copy of the CG file  1132  is a file  1132 ′. The file  1132 ′ is a point-in-time copy of the CG file  1122 ′ and includes metadata  1144 ′, an example of metadata  1144 . 
     Referring to  FIG. 14 , a process  1400  is an example of a process to protect data using the data protection system  1100 . Process  1400  copies a first volume to a consistency group file at the backup device ( 1402 ). For example, the DPA  1104  replicates the first storage volume  1108   a  to the CG file  1122 . 
     Process  1400  determines if there are additional volumes to replicate and if there are, process  1400  copies the volumes to the CG file ( 1406 ). For example, the DPA  1104  replicates the second storage volume  1108   b  to the CG file  1122  and the DPA  1104  replicates the third storage volume  1108   c  to the CG file  1122 . 
     Referring to  FIG. 15 , a process  1500  is an example of a process to restore protected data. Process  1500  copies the CG file ( 1502 ). For example, the CG file  1122  is copied to become the first copy of CG File  1132  and the copy process, for example, is a fast copy doing a metadata operation only. 
     Process  1500  extracts a volume using synthesis ( 1506 ). For example, the process in  FIG. 9  is used to extract a volume. In one particular example, to extract a replica of a first volume  1108   a ′, the process  900  in  FIG. 9  is used to copy data from the 0 offset to the 1 GB offset to a new file  1142   a ′ of size 1 GB (see  FIG. 13C ). In one example, the copy operation for extracting a volume from the CG file is a metadata operation and does not do any actual data copying and thus is very efficient. 
     Process  1500  exposes the extracted volume to the user ( 1510 ). For example the extracted volume is exposed as a logical unit for a user to access. 
     Referring to  FIG. 16 , a process  1600  is an example of a process to add a volume to a consistency group (CG) file. Process  1600  receives notification that a new volume was added ( 1602 ) and adds a volume to the end of the CG file ( 1606 ). For example, after a notification is received that a consistency group includes a new volume, the new volume is added to the end of the CG file  1122 , i.e., the file size is increased and the last offset of the file are part of the new volume. For example, a CG file  1122 ″ is formed by placing a new volume  1202  of size 1 GB at the end of the CG file  1122 ′ (see  FIG. 13D ). 
     Referring to  FIG. 17 , a process  1700  is an example of a process to remove a volume from the CG file. Process  1700  receives notification that a volume in a CG file has been removed ( 1702 ) and process  1700  extracts each volume to a separate file ( 1706 ) (e.g., using the synthesis process (e.g., the process  900  in  FIG. 9 )). For example, the copies of the files  1142   a - 1142   c  are generated (e.g., using the process  1400 ). 
     Process  1700  copies all the volumes back to a new CG file except the deleted volume ( 1708 ). For example, if the second storage volume is deleted then copies of the first and third volumes  1142   a ,  1142   c  are copied to a CG file  1122 ′″ (see  FIG. 13E ). 
     Referring to  FIG. 18 , a process  1800  is an example of a process to resize a volume in the CG file in the data protection system of  FIG. 11 . Process  1800  receives notification that a volume is being resized ( 1802 ) and process  1800  extracts each volume to a separate file ( 1806 ) (e.g., using the synthesis process (e.g., the process  900  in  FIG. 9 )). For example, the copies of the files  1142   a - 1142   c  are generated (e.g., using the process  1400 ). 
     Process  1800  copies all the volumes back to a new CG file accommodating the new volume size ( 1808 ). For example, if the third storage volume is increased by 1 GB, then the first, second third volumes from copies  1142   a - 1142   c  are copied to a new CG file  1122 ″″ (see  FIG. 13F ). 
     Referring to  FIG. 19 , in one example, a computer  1900  includes a processor  1902 , a volatile memory  1904 , a non-volatile memory  1906  (e.g., hard disk) and the user interface (UI)  1908  (e.g., a graphical user interface, a mouse, a keyboard, a display, touch screen and so forth). The non-volatile memory  1906  stores computer instructions  1912 , an operating system  1916  and data  1918 . In one example, the computer instructions  1912  are executed by the processor  1902  out of volatile memory  1904  to perform all or part of the processes described herein (e.g., processes  400 ,  700 ,  712 ,  900 ,  1200 ,  1400 ,  1500 ,  1600 ,  1700  and  1800 ). 
     The processes described herein (e.g., processes  400 ,  700 ,  712 ,  900 ,  1200 ,  1400 ,  1500 ,  1600 ,  1700  and  1800 ) are not limited to use with the hardware and software of  FIG. 19 ; they may find applicability in any computing or processing environment and with any type of machine or set of machines that is capable of running a computer program. The processes described herein may be implemented in hardware, software, or a combination of the two. The processes described herein may be implemented in computer programs executed on programmable computers/machines that each includes a processor, a non-transitory machine-readable medium or other article of manufacture that is readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and one or more output devices. Program code may be applied to data entered using an input device to perform any of the processes described herein and to generate output information. 
     The system may be implemented, at least in part, via a computer program product, (e.g., in a non-transitory machine-readable storage medium such as, for example, a non-transitory computer-readable medium), for execution by, or to control the operation of, data processing apparatus (e.g., a programmable processor, a computer, or multiple computers). Each such program may be implemented in a high level procedural or object-oriented programming language to communicate with a computer system. However, the programs may be implemented in assembly or machine language. The language may be a compiled or an interpreted language and it may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program may be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. A computer program may be stored on a non-transitory machine-readable medium that is readable by a general or special purpose programmable computer for configuring and operating the computer when the non-transitory machine-readable medium is read by the computer to perform the processes described herein. For example, the processes described herein may also be implemented as a non-transitory machine-readable storage medium, configured with a computer program, where upon execution, instructions in the computer program cause the computer to operate in accordance with the processes. A non-transitory machine-readable medium may include but is not limited to a hard drive, compact disc, flash memory, non-volatile memory, volatile memory, magnetic diskette and so forth but does not include a transitory signal per se. 
     The processes described herein are not limited to the specific examples described. For example, the processes  400 ,  700 ,  712 ,  900 ,  1200 ,  1400 ,  1500 ,  1600 ,  1700  and  1800  are not limited to the specific processing order of  FIGS. 4, 7, 7A, 9, 12 and 14 to 18 , respectively. Rather, any of the processing blocks of  FIGS. 4, 7, 7A, 9, 12 and 14 to 18  may be re-ordered, combined or removed, performed in parallel or in serial, as necessary, to achieve the results set forth above. 
     The processing blocks (for example, in the processes  400 ,  700 ,  712 ,  900 ,  1200 ,  1400 ,  1500 ,  1600 ,  1700  and  1800 ) associated with implementing the system may be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or part of the system may be implemented as, special purpose logic circuitry (e.g., an FPGA (field-programmable gate array) and/or an ASIC (application-specific integrated circuit)). All or part of the system may be implemented using electronic hardware circuitry that include electronic devices such as, for example, at least one of a processor, a memory, a programmable logic device or a logic gate. 
     Elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Various elements, which are described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims.