Abstract:
In a dispersed storage network, data objects are dispersed storage error encoded into pluralities of sets of encoded data slices that are stored in a set of storage units. To recover a data object, a read threshold number of encoded data slices from each set of encoded data slices of a corresponding set of the plurality of sets of encoded data slices are required. Upon determining that an update is available for the set of storage units, a dispersed storage managing unit takes a first subset of storage units off line to perform the update. During the update, a remaining number of storage units of the set of storage units remain on line such that at least the read threshold number of encoded data slices are available for each set of the pluralities of sets of encoded data slices.

Description:
CROSS-REFERENCE TO RELATED PATENTS 
     The present U.S. Utility patent application claims priority pursuant to 35 U.S.C. §120, as a continuation of U.S. Utility patent application Ser. No. 14/132,020, entitled “DISTRIBUTED STORAGE NETWORK FOR MODIFICATION OF A DATA OBJECT”, filed Dec. 18, 2013, now issued as U.S. Pat. No. 8,914,707 on Dec. 16, 2014, which is a continuation of U.S. Utility patent application Ser. No. 13/932,320, entitled “DISTRIBUTED STORAGE NETWORK FOR MODIFICATION OF A DATA OBJECT,” filed Jul. 1, 2013, now issued as U.S. Pat. No. 8,631,303 on Jan. 14, 2014, which is a continuation of U.S. Utility patent application Ser. No. 12/839,197, entitled “DISTRIBUTED STORAGE NETWORK FOR MODIFICATION OF A DATA OBJECT,” filed Jul. 19, 2010, now issued as U.S. Pat. No. 8,479,078 on Jul. 2, 2013, which claims priority pursuant to 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/256,436 entitled “DISTRIBUTED STORAGE NETWORK ACCESS,” filed Oct. 30, 2009, all of which are hereby incorporated herein by reference in their entirety and made part of the present U.S. Utility patent application for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     This invention relates generally to computing systems and more particularly to data storage within such computing systems. 
     2. Description of Related Art 
     This invention relates generally to computing systems and more particularly to data storage solutions within such computing systems. 
     DESCRIPTION OF RELATED ART 
     Computers are known to communicate, process, and store data. Such computers range from wireless smart phones to data centers that support millions of web searches, stock trades, or on-line purchases every day. In general, a computing system generates data and/or manipulates data from one form into another. For instance, an image sensor of the computing system generates raw picture data and using an image compression program (e.g., JPEG, MPEG, etc.), the computing system manipulates the raw picture data into a standardized compressed image. 
     With continued advances in processing speed and communication speed, computers are capable of processing real time multimedia data for applications ranging from simple voice communications to streaming high definition video. As such, general-purpose information appliances are replacing purpose-built communications devices (e.g., a telephone). For example, smart phones can support telephony communications but they are also capable of text messaging and accessing the internet to perform functions including email, web browsing, remote applications access, and media communications (e.g., telephony voice, image transfer, music files, video files, real time video streaming, etc.). 
     Each type of computer is constructed and operates in accordance with one or more communication, processing, and storage standards. As a result of standardization and with advances in technology, more and more information content is being converted into digital formats. For example, more digital cameras are now being sold than film cameras, thus producing more digital pictures. As another example, web-based programming is becoming an alternative to over the air television broadcasts and/or cable broadcasts. As further examples, papers, books, video entertainment, home video, etc. are now being stored digitally. This increased storage of information content increases the demand on the storage function of computers. 
     A typical computer storage system includes one or more memory devices aligned with the needs of the various operational aspects of the computer&#39;s processing and communication functions. Generally, the immediacy of access dictates what type of memory device is used. For example, random access memory (RAM) memory can be accessed in any random order with a constant response time, thus it is typically used for cache memory and main memory. By contrast, memory device technologies that require physical movement such as magnetic disks, tapes, and optical discs, have a variable response time as the physical movement can take longer than the data transfer, thus they are typically used for secondary memory (e.g., hard drive, backup memory, etc.). 
     A computer&#39;s storage system will be compliant with one or more computer storage standards that include, but are not limited to, network file system (NFS), flash file system (FFS), disk file system (DFS), small computer system interface (SCSI), internet small computer system interface (iSCSI), file transfer protocol (FTP), and web-based distributed authoring and versioning (WebDAV). These standards specify the data storage format (e.g., files, data objects, data blocks, directories, etc.) and interfacing between the computer&#39;s processing function and its storage system, which is a primary function of the computer&#39;s memory controller. 
     Despite the standardization of the computer and its storage system, memory devices fail; especially commercial grade memory devices that utilize technologies incorporating physical movement (e.g., a disc drive). For example, it is fairly common for a disc drive to routinely suffer from bit level corruption and to completely fail after three years of use. One solution is to utilize a higher-grade disc drive, which adds significant cost to a computer. 
     Another solution is to utilize multiple levels of redundant disc drives to replicate the data into two or more copies. One such redundant drive approach is called redundant array of independent discs (RAID). In a RAID device, a RAID controller adds parity data to the original data before storing it across the array. The parity data is calculated from the original data such that the failure of a disc will not result in the loss of the original data. For example, RAID 5 uses three discs to protect data from the failure of a single disc. The parity data, and associated redundancy overhead data, reduces the storage capacity of three independent discs by one third (e.g., n−1=capacity). RAID 6 can recover from a loss of two discs and requires a minimum of four discs with a storage capacity of n−2. 
     While RAID addresses the memory device failure issue, it is not without its own failure issues that affect its effectiveness, efficiency and security. For instance, as more discs are added to the array, the probability of a disc failure increases, which increases the demand for maintenance. For example, when a disc fails, it needs to be manually replaced before another disc fails and the data stored in the RAID device is lost. To reduce the risk of data loss, data on a RAID device is typically copied on to one or more other RAID devices. While this addresses the loss of data issue, it raises a security issue since multiple copies of data are available, which increases the chances of unauthorized access. Further, as the amount of data being stored grows, the overhead of RAID devices becomes a non-trivial efficiency issue. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  is a schematic block diagram of an embodiment of a computing system in accordance with the invention; 
         FIG. 2  is a schematic block diagram of an embodiment of a computing core in accordance with the invention; 
         FIG. 3  is a schematic block diagram of an embodiment of a distributed storage processing unit in accordance with the invention; 
         FIG. 4  is a schematic block diagram of an embodiment of a grid module in accordance with the invention; 
         FIG. 5  is a diagram of an example embodiment of error coded data slice creation in accordance with the invention; 
         FIG. 6  is a schematic block diagram of an embodiment of a file system hierarchy in accordance with the invention; 
         FIG. 7  is a schematic block diagram of an embodiment of a segment and slice directory in accordance with the invention; 
         FIG. 8  is a logic flow diagram of an embodiment of a method for modifying a data object in accordance with the invention; 
         FIG. 9  is a logic flow diagram of an embodiment of a method for identifying a data segment of a data object for modification in accordance with the invention; 
         FIG. 10  is a schematic block diagram of an embodiment of a modification request in accordance with the invention; 
         FIG. 11  is a logic flow diagram of another embodiment of a method for modifying a data object in accordance with the invention; 
         FIG. 12  is a logic flow diagram of another embodiment of a method for modifying a data object in accordance with the invention; 
         FIG. 13  is a schematic block diagram of an embodiment of a write request in accordance with the invention; 
         FIG. 14  is a logic flow diagram of an embodiment of a method for generating and storing rebuilt encoded data slices from a modified data segment in accordance with the invention; 
         FIG. 15  is a schematic block diagram of an embodiment of a data segment header in accordance with the invention; 
         FIG. 16  is a logic flow diagram of another embodiment of a method for modifying a data object in accordance with the invention; 
         FIG. 17  is a logic flow diagram of an embodiment of a method for updating a system element in accordance with the invention; and 
         FIG. 18  is a logic flow diagram of another embodiment of a method for updating a system element in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic block diagram of a computing system  10  that includes one or more of a first type of user devices  12 , one or more of a second type of user devices  14 , at least one distributed storage (DS) processing unit  16 , at least one DS managing unit  18 , at least one storage integrity processing unit  20 , and a distributed storage network (DSN) memory  22  coupled via a network  24 . The network  24  may include one or more wireless and/or wire lined communication systems; one or more private intranet systems and/or public internet systems; and/or one or more local area networks (LAN) and/or wide area networks (WAN). 
     The DSN memory  22  includes a plurality of distributed storage (DS) units  36  for storing data of the system. Each of the DS units  36  includes a processing module and memory and may be located at a geographically different site than the other DS units (e.g., one in Chicago, one in Milwaukee, etc.). The processing module may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or operational instructions. The processing module may have an associated memory and/or memory element, which may be a single memory device, a plurality of memory devices, and/or embedded circuitry of the processing module. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that if the processing module includes more than one processing device, the processing devices may be centrally located (e.g., directly coupled together via a wired and/or wireless bus structure) or may be distributedly located (e.g., cloud computing via indirect coupling via a local area network and/or a wide area network). Further note that when the processing module implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory and/or memory element storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. Still further note that, the memory element stores, and the processing module executes, hard coded and/or operational instructions corresponding to at least some of the steps and/or functions illustrated in  FIGS. 1-18 . 
     Each of the user devices  12 - 14 , the DS processing unit  16 , the DS managing unit  18 , and the storage integrity processing unit  20  may be a portable computing device (e.g., a social networking device, a gaming device, a cell phone, a smart phone, a personal digital assistant, a digital music player, a digital video player, a laptop computer, a handheld computer, a video game controller, and/or any other portable device that includes a computing core) and/or a fixed computing device (e.g., a personal computer, a computer server, a cable set-top box, a satellite receiver, a television set, a printer, a fax machine, home entertainment equipment, a video game console, and/or any type of home or office computing equipment). Such a portable or fixed computing device includes a computing core  26  and one or more interfaces  30 ,  32 , and/or  38 . An embodiment of the computing core  26  will be described with reference to  FIG. 2 . 
     With respect to the interfaces, each of the interfaces  30 ,  32 , and  38  includes software and/or hardware to support one or more communication links via the network  24  and/or directly. For example, interfaces  30  support a communication link (wired, wireless, direct, via a LAN, via the network  24 , etc.) between the first type of user device  14  and the DS processing unit  16 . As another example, DSN interface  32  supports a plurality of communication links via the network  24  between the DSN memory  22  and the DS processing unit  16 , the first type of user device  12 , and/or the storage integrity processing unit  20 . As yet another example, interface  38  supports a communication link between the DS managing unit  18  and any one of the other devices and/or units  12 ,  14 ,  16 ,  20 , and/or  22  via the network  24 . 
     In general and with respect to data storage, the system  10  supports three primary functions: distributed network data storage management, distributed data storage and retrieval, and data storage integrity verification. In accordance with these three primary functions, data can be distributedly stored in a plurality of physically different locations and subsequently retrieved in a reliable and secure manner regardless of failures of individual storage devices, failures of network equipment, the duration of storage, the amount of data being stored, attempts at hacking the data, etc. 
     The DS managing unit  18  performs distributed network data storage management functions, which include establishing distributed data storage parameters, performing network operations, performing network administration, and/or performing network maintenance. The DS managing unit  18  establishes the distributed data storage parameters (e.g., allocation of virtual DSN memory space, distributed storage parameters, security parameters, billing information, user profile information, etc.) for one or more of the user devices  12 - 14  (e.g., established for individual devices, established for a user group of devices, established for public access by the user devices, etc.). For example, the DS managing unit  18  coordinates the creation of a vault (e.g., a virtual memory block) within the DSN memory  22  for a user device (for a group of devices, or for public access). The DS managing unit  18  also determines the distributed data storage parameters for the vault. In particular, the DS managing unit  18  determines a number of slices (e.g., the number that a data segment of a data file and/or data block is partitioned into for distributed storage) and a read threshold value (e.g., the minimum number of slices required to reconstruct the data segment). 
     As another example, the DS managing module  18  creates and stores, locally or within the DSN memory  22 , user profile information. The user profile information includes one or more of authentication information, permissions, and/or the security parameters. The security parameters may include one or more of encryption/decryption scheme, one or more encryption keys, key generation scheme, and data encoding/decoding scheme. 
     As yet another example, the DS managing unit  18  creates billing information for a particular user, user group, vault access, public vault access, etc. For instance, the DS managing unit  18  tracks the number of times a user accesses a private vault and/or public vaults, which can be used to generate a per-access bill. In another instance, the DS managing unit  18  tracks the amount of data stored and/or retrieved by a user device and/or a user group, which can be used to generate a per-data-amount bill. 
     The DS managing unit  18  also performs network operations, network administration, and/or network maintenance. As at least part of performing the network operations and/or administration, the DS managing unit  18  monitors performance of the devices and/or units of the system  10  for potential failures, determines the devices&#39; and/or units&#39; activation status, determines the devices&#39; and/or units&#39; loading, and any other system level operation that affects the performance level of the system  10 . For example, the DS managing unit  18  receives and aggregates network management alarms, alerts, errors, status information, performance information, and messages from the devices  12 - 14  and/or the units  16 ,  20 ,  22 . For example, the DS managing unit  18  receives a simple network management protocol (SNMP) message regarding the status of the DS processing unit  16 . 
     The DS managing unit  18  performs the network maintenance by identifying equipment within the system  10  that needs replacing, upgrading, repairing, and/or expanding. For example, the DS managing unit  18  determines that the DSN memory  22  needs more DS units  36  or that one or more of the DS units  36  needs updating. 
     The second primary function (i.e., distributed data storage and retrieval) begins and ends with a user device  12 - 14 . For instance, if a second type of user device  14  has a data object  40 , such as a data file and/or data block, to store in the DSN memory  22 , it sends the data object  40  to the DS processing unit  16  via its interface  30 . As will be described in greater detail with reference to  FIG. 2 , the interface  30  functions to mimic a conventional operating system (OS) file system interface (e.g., network file system (NFS), flash file system (FFS), disk file system (DFS), file transfer protocol (FTP), web-based distributed authoring and versioning (WebDAV), etc.) and/or a block memory interface (e.g., small computer system interface (SCSI), internet small computer system interface (iSCSI), etc.). In addition, the interface  30  may attach a user identification code (ID) to the data object  40 . 
     The DS processing unit  16  receives the data object  40  via its interface  30  and performs a distributed storage (DS) process  34  thereon (e.g., an error coding dispersal storage function). The DS processing  34  begins by partitioning the data object  40  into one or more data segments, which is represented as Y data segments. The DS processing  34  may partition the data object  40  into fixed byte size segments (e.g., 21 to 2n bytes, where n=&gt;2) or variable byte size segments (e.g., change byte size from segment to segment, or from groups of segments to groups of segments, etc.). 
     For example, in  FIG. 1  for each of the Y number of data segments  42   a - n , the DS processing  34  error encodes (e.g., forward error correction (FEC), information dispersal algorithm, or error correction coding) and slices (or slices then error encodes) the data segments  42   a - n  into a plurality of error coded (EC) data slices  42   a - 42   n  and  46   a - 46   n , which are represented as X slices per data segment. The number of slices (X) per segment, which corresponds to a number of pillars n, is set in accordance with the distributed data storage parameters and the error coding scheme. For example, if a Reed-Solomon (or other FEC scheme) is used in an X/T system, then a data segment is divided into X number of slices, where T number of slices are needed to reconstruct the original data (i.e., T is the threshold). As a few specific examples, the X/T factor may be 5/3; 6/4; 8/6; 8/5; 16/10. 
     For each slice  44   a - n  and  46   a - n , the DS processing unit  16  creates a unique slice name and appends it to the corresponding slice. The slice name includes universal DSN memory addressing routing information (e.g., virtual memory addresses in the DSN memory  22 ) and user-specific information (e.g., user ID, file name, data block identifier, etc.). 
     The DS processing unit  16  transmits the plurality of EC slices  44   a - n  and  46   a - n  to a plurality of DS units  36  of the DSN memory  22  via the DSN interface  32  and the network  24 . The DSN interface  32  formats each of the slices for transmission via the network  24 . For example, the DSN interface  32  may utilize an internet protocol (e.g., TCP/IP, etc.) to packetize the slices  44   a - n  and  46   a - n  for transmission via the network  24 . 
     The number of DS units  36  receiving the slices  44   a - n  and  46   a - n  is dependent on the distributed data storage parameters established by the DS managing unit  18 . For example, the DS managing unit  18  may indicate that each slice is to be stored in a different DS unit  36 . As another example, the DS managing unit  18  may indicate that like slice numbers of different data segments are to be stored in the same DS unit  36 . For example, the first slice  44   a  and  46   a  of each of the data segments  42   a - n  is to be stored in a first DS unit  36 , the second slice  44   b  and  46   b  of each of the data segments  42   a - n  is to be stored in a second DS unit  36 , etc. In this manner, the data is encoded and distributedly stored at physically diverse locations to improve data storage integrity and security. Further examples of encoding the data segments will be provided with reference to one or more of  FIGS. 2-18 . 
     Each DS unit  36  that receives a slice for storage translates the virtual DSN memory address of the slice into a local physical address for storage. Accordingly, each DS unit  36  maintains a virtual to physical memory mapping to assist in the storage and retrieval of data. 
     The first type of user device  12  performs a similar function to store data in the DSN memory  22  with the exception that it includes the DS processing. As such, the device  12  encodes and slices the data file and/or data block it has to store. The device then transmits the slices  11  to the DSN memory via its DSN interface  32  and the network  24 . 
     For a second type of user device  14  to retrieve a data file or data block from memory, it issues a read command via its interface  30  to the DS processing unit  16 . The DS processing unit  16  performs the DS processing  34  to identify the DS units  36  storing the slices of the data file and/or data block based on the read command. The DS processing unit  16  may also communicate with the DS managing unit  18  to verify that the user device  14  is authorized to access the requested data. 
     Assuming that the user device is authorized to access the requested data, the DS processing unit  16  issues slice read commands to at least a threshold number of the DS units  36  storing the requested data (e.g., to at least 10 DS units for a 16/10 error coding scheme). Each of the DS units  36  receiving the slice read command, verifies the command, accesses its virtual to physical memory mapping, retrieves the requested slice, or slices, and transmits it to the DS processing unit  16 . 
     Once the DS processing unit  16  has received a read threshold number of slices for a data segment, it performs an error decoding function and de-slicing to reconstruct the data segment. When Y number of data segments has been reconstructed, the DS processing unit  16  provides data object  40  to the user device  14 . Note that the first type of user device  12  performs a similar process to retrieve data object  40 . 
     The storage integrity processing unit  20  performs the third primary function of data storage integrity verification. In general, the storage integrity processing unit  20  periodically retrieves slices  48 , and/or slice names, of a data object  40  to verify that one or more slices have not been corrupted or lost (e.g., the DS unit failed). The retrieval process mimics the read process previously described. 
     If the storage integrity processing unit  20  determines that one or more slices  48  is corrupted or lost, it rebuilds the corrupted or lost slice(s) in accordance with the error coding scheme. The storage integrity processing unit  20  stores the rebuilt slice, or slices, in the appropriate DS unit(s)  36  in a manner that mimics the write process previously described. 
       FIG. 2  is a schematic block diagram of an embodiment of a computing core  26  that includes a processing module  50 , a memory controller  52 , main memory  54 , a video graphics processing unit  55 , an input/output (IO) controller  56 , a peripheral component interconnect (PCI) interface  58 , at least one IO interface  60 ,  10  device interface module  62 , a read only memory (ROM) basic input output system (BIOS)  64 , and one or more memory interface modules. The memory interface module(s) includes one or more of a universal serial bus (USB) interface module  66 , a host bus adapter (HBA) interface module  68 , a network interface module  70 , a flash interface module  72 , a hard drive interface module  74 , and a DSN interface module  76 . Note the DSN interface module  76  and/or the network interface module  70  may function as the interface  30  of the user device  14  of  FIG. 1 . Further note that the IO device interface module  62  and/or the memory interface modules may be collectively or individually referred to as IO ports. 
     The processing module  50  may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on hard coding of the circuitry and/or operational instructions. The processing module  50  may have an associated memory and/or memory element, which may be a single memory device, a plurality of memory devices, and/or embedded circuitry of the processing module  50 . Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, cache memory, and/or any device that stores digital information. Note that if the processing module  50  includes more than one processing device, the processing devices may be centrally located (e.g., directly coupled together via a wired and/or wireless bus structure) or may be distributedly located (e.g., cloud computing via indirect coupling via a local area network and/or a wide area network). Further note that when the processing module  50  implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory and/or memory element storing the corresponding operational instructions may be embedded within, or external to, the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. Still further note that, the memory element stores, and the processing module  50  executes, hard coded and/or operational instructions corresponding to at least some of the steps and/or functions illustrated in  FIGS. 1-18 . 
       FIG. 3  is a schematic block diagram of an embodiment of a dispersed storage (DS) processing module  34  of user device  12  and/or of the DS processing unit  16 . The DS processing module  34  includes a gateway module  78 , an access module  80 , a grid module  82 , and a storage module  84 . The DS processing module  34  may also include an interface  30  and DSN interface  32  or the interfaces  30  and/or  32  may be part of user  12  or of the DS processing unit  14 . The DS processing module  34  may further include a bypass/feedback path between the storage module  84  to the gateway module  78 . Note that the modules  78 - 84  of the DS processing module  34  may be in a single unit or distributed across multiple units. 
     In an example of storing data, the gateway module  78  receives an incoming request with a data object  40 . The incoming request may also include a user ID field  86 , an object name field  88  and other corresponding information such as a process identifier (e.g., an internal process/application ID), metadata, a file system directory, a block number, a transaction message, a user device identity (ID), a data object identifier, a source name, and/or user information. The gateway module  78  authenticates the user associated with the data object by verifying the user ID  86  with the managing unit  18  and/or another authenticating unit. 
     When the user is authenticated, the gateway module  78  obtains user information from the management unit  18 , the user device  12 -Source  14 , and/or the other authenticating unit. The user information includes a vault identifier, operational parameters, and user attributes (e.g., user data, billing information, etc.). A vault identifier identifies a vault, which is a virtual memory space that maps to a set of DS storage units  36 . For example, vault 1 (i.e., user 1&#39;s DSN memory space) includes eight DS storage units (X=8 wide) and vault 2 (i.e., user 2&#39;s DSN memory space) includes sixteen DS storage units (X=16 wide). The operational parameters may include an error coding algorithm, the width n (number of pillars X or slices per segment for this vault), a read threshold T, a write threshold, an encryption algorithm, a slicing parameter, a compression algorithm, an integrity check method, caching settings, parallelism settings, and/or other parameters that may be used to access the DSN memory layer. 
     The gateway module  78  uses the user information to assign a source name  35  to the data object  40 . For instance, the gateway module  78  determines the source name  35  of the data object  40  based on the vault identifier and the data object  40 . For example, the source name may contain a file identifier (ID), a vault generation number, a reserved field, and a vault identifier (ID). As another example, the gateway module  78  may generate the file ID based on a hash function of the data object  40 . Note that the gateway module  78  may also perform message conversion, protocol conversion, electrical conversion, optical conversion, access control, user identification, user information retrieval, traffic monitoring, statistics generation, configuration, management, and/or source name determination. 
     The access module  80  receives the data object  40  and creates a plurality of data segments 1 through Y  42   a - n  in accordance with a data storage protocol (e.g., file storage system, a block storage system, and/or an aggregated block storage system). The number Y of data segments may be fixed with a segment size depending on the data object size or the number of segments may vary with a fixed segment size. For example, when the number Y of segments is chosen to be a fixed number, then the size of the segments varies as a function of the size of the data object. For instance, if the data object is an image file of 4,194,304 eight bit bytes (e.g., 33,554,432 bits) and the number of segments Y=131,072, then each segment is 256 bits or 32 bytes. As another example, when the segment size is fixed, then the number of segments Y varies based on the size of data object. For instance, if the data object is an image file of 4,194,304 bytes and the fixed segment size of each segment is 4,096 bytes, then the number of segments Y=1,024. Note that each segment is associated with the same source name  35 . 
     The grid module  82  receives the Y data segments and may manipulate (e.g., compression, encryption, cyclic redundancy check (CRC), etc.) each of the data segments before performing an error coding function of the error coding dispersal storage function to produce a pre-manipulated data segment. After manipulating a data segment, if applicable, the grid module  82  error encodes (e.g., Reed-Solomon, Convolution encoding, Trellis encoding, etc.) the data segment or manipulated data segment into X error coded data slices  42 - 44 . 
     The value X, or the number of pillars (e.g., X=16), is chosen as a parameter of the error coding dispersal storage function. Other parameters of the error coding dispersal function include a read threshold T, a write threshold W, etc. The read threshold (e.g., T=10, when X=16) corresponds to the minimum number of error coded data slices required to reconstruct the data segment. In other words, the DS processing module  34  can compensate for X-T (e.g., 16−10=6) missing error coded data slices per data segment. The write threshold W corresponds to a minimum number of DS storage units that acknowledge proper storage of their respective data slices before the DS processing module indicates proper storage of the encoded data segment. Note that the write threshold W is greater than or equal to the read threshold T (i.e., W≧T) for a given number of pillars (X). 
     For each data slice of a data segment, the grid module  82  generates a unique slice name  37  and attaches it thereto. The slice name  37  includes a universal routing information field and a vault specific field and may be 48 bytes (e.g., 24 bytes for each of the universal routing information field and the vault specific field). As illustrated, the universal routing information field includes a slice index, a vault ID, a vault generation, and a reserved field. The slice index is based on the pillar number n and the vault ID and, as such, is unique for each pillar (e.g., slices of the same pillar for the same vault for any segment will share the same slice index). The vault specific field includes a data name, which includes a file ID and a segment number (e.g., a sequential numbering of data segments 1-Y of a simple data object or a data block number). 
     Prior to outputting the error coded data slices of a data segment, the grid module may perform post-slice manipulation on the slices. If enabled, the manipulation includes slice level compression, encryption, CRC, addressing, tagging, and/or other manipulation to improve the effectiveness of the computing system. 
     When the error coded (EC) data slices of a data segment are ready for storage, the grid module  82  determines which of the DS storage units  36  will store the EC data slices based on a dispersed storage memory mapping associated with the user&#39;s vault and/or DS storage unit  36  attributes. The DS storage unit attributes may include availability, self-selection, performance history, link speed, link latency, ownership, available DSN memory, domain, cost, a prioritization scheme, a centralized selection message from another source, a lookup table, data ownership, and/or any other factor to optimize the operation of the computing system. Note that the number of DS storage units  36  in an embodiment is equal to or greater than the number of pillars (e.g., X) so that no more than one error coded data slice of the same data segment is stored on the same DS storage unit  36 . Further note that EC data slices of the same pillar number but of different segments (e.g., EC data slice 1 of data segment 1 and EC data slice 1 of data segment 2) may be stored on the same or different DS storage units  36 . 
     The storage module  84  performs an integrity check on the outbound encoded data slices and, when successful, identifies a plurality of DS storage units based on information provided by the grid module. The storage module then outputs the encoded data slices  1  through X of each segment 1 through Y to the DS storage units. Each of the DS storage units  36  stores its EC data slice(s) and maintains a local virtual DSN address to physical location table to convert the virtual DSN address of the EC data slice(s) into physical storage addresses. 
     In an example of a read operation, the user device  12  and/or  14  sends a read request to the DS processing  34 , which authenticates the request. When the request is authentic, the DS processing  34  sends a read message to each of the DS storage units  36  storing slices of the data object being read. The slices are received via the DSN interface  32  and processed by the storage module  84 , which performs a parity check and provides the slices to the grid module  82  when the parity check is successful. The grid module  82  decodes the slices in accordance with the error coding dispersal storage function to reconstruct the data segment. The access module  80  reconstructs the data object from the data segments and the gateway module  78  formats the data object for transmission to the user device. 
       FIG. 4  is a schematic block diagram of an embodiment of a grid module  82  that includes a control unit  73 , a pre-slice manipulator  75 , an encoder  77 , a slicer  79 , a post-slice manipulator  81 , a pre-slice de-manipulator  83 , a decoder  85 , a de-slicer  87 , and/or a post-slice de-manipulator  89 . Note that the control unit  73  may be partially or completely external to the grid module  82 . For example, the control unit  73  may be part of the computing core at a remote location, part of a user device, part of the DS managing unit  18 , or distributed amongst one or more DS storage units. 
     In an example of write operation, the pre-slice manipulator  75  receives a data segment  42  and a write instruction from an authorized user device. The pre-slice manipulator  75  determines if pre-manipulation of the data segment  42  is required and, if so, what type. The pre-slice manipulator  75  may make the determination independently or based on instructions from the control unit  73 , where the determination is based on a computing system-wide predetermination, a table lookup, vault parameters associated with the user identification, the type of data, security requirements, available DSN memory, performance requirements, and/or other metadata. 
     Once a positive determination is made, the pre-slice manipulator  75  manipulates the data segment  42  in accordance with the type of manipulation. For example, the type of manipulation may be compression (e.g., Lempel-Ziv-Welch, Huffman, Golomb, fractal, wavelet, etc.), signatures (e.g., Digital Signature Algorithm (DSA), Elliptic Curve DSA, Secure Hash Algorithm, etc.), watermarking, tagging, encryption (e.g., Data Encryption Standard, Advanced Encryption Standard, etc.), adding metadata (e.g., time/date stamping, user information, file type, etc.), cyclic redundancy check (e.g., CRC32), and/or other data manipulations to produce the pre-manipulated data segment. 
     The encoder  77  encodes the pre-manipulated data segment  42  using a forward error correction (FEC) encoder (and/or other type of erasure coding and/or error coding) to produce an encoded data segment 94. The encoder  77  determines which forward error correction algorithm to use based on a predetermination associated with the user&#39;s vault, a time based algorithm, user direction, DS managing unit direction, control unit direction, as a function of the data type, as a function of the data segment  42  metadata, and/or any other factor to determine algorithm type. The forward error correction algorithm may be Golay, Multidimensional parity, Reed-Solomon, Hamming, Bose Ray Chauduri Hocquenghem (BCH), Cauchy-Reed-Solomon, or any other FEC encoder. Note that the encoder  77  may use a different encoding algorithm for each data segment  42 , the same encoding algorithm for the data segments  42  of a data object, or a combination thereof. 
     The encoded data segment  94  is of greater size than the data segment  42  by the overhead rate of the encoding algorithm by a factor of X/T, where X is the width or number of slices, and T is the read threshold. In this regard, the corresponding decoding process can accommodate at most X-T missing EC data slices and still recreate the data segment 42. For example, if X=16 and T=10, then the data segment  42  will be recoverable as long as 10 or more EC data slices per data segment are not corrupted. 
     The slicer  79  transforms the encoded data segment  94  into EC data slices in accordance with the slicing parameter from the vault for this user and/or data segment 42. For example, if the slicing parameter is X=16, then the slicer slices each encoded data segment  94  into 16 encoded slices. 
     The post-slice manipulator  81  performs, if enabled, post-manipulation on the encoded slices to produce the EC data slices. If enabled, the post-slice manipulator  81  determines the type of post-manipulation, which may be based on a computing system-wide predetermination, parameters in the vault for this user, a table lookup, the user identification, the type of data, security requirements, available DSN memory, performance requirements, control unit directed, and/or other metadata. Note that the type of post-slice manipulation may include slice level compression, signatures, encryption, CRC, addressing, watermarking, tagging, adding metadata, and/or other manipulation to improve the effectiveness of the computing system. 
     In an example of a read operation, the post-slice de-manipulator  89  receives at least a read threshold number of EC data slices and performs the inverse function of the post-slice manipulator  81  to produce a plurality of encoded slices. The de-slicer  87  de-slices the encoded slices to produce an encoded data segment  94 . The decoder  85  performs the inverse function of the encoder  77  to recapture the data segment  42 . The pre-slice de-manipulator  83  performs the inverse function of the pre-slice manipulator  75  to recapture the data segment. 
       FIG. 5  is a diagram of an example of slicing an encoded data segment  94  by the slicer  79 . In this example, the encoded data segment includes thirty-two bits, but may include more or less bits. The slicer  79  disperses the bits of the encoded data segment  94  across the EC data slices in a pattern as shown. As such, each EC data slice does not include consecutive bits of the data segment  94  reducing the impact of consecutive bit failures on data recovery. For example, if EC data slice 2 (which includes bits  1 ,  5 ,  9 ,  13 ,  17 ,  25 , and  29 ) is unavailable (e.g., lost, inaccessible, or corrupted), the data segment can be reconstructed from the other EC data slices (e.g., 1, 3 and 4 for a read threshold of 3 and a width of 4). 
       FIG. 6  is a schematic block diagram of an embodiment of a file system hierarchy including a plurality of user virtual memories in a virtual DSN address space  148 , a virtual dispersed storage network (DSN) address to physical location table  142 , and a physical dispersed storage network (DSN) memory  22 . The file system hierarchy is an illustration of translating a user virtual memory address space  152  into a virtual dispersed storage network (DSN) address space  148  and then to a physical address in a DSN memory  22 . In this illustration, the physical DSN memory  22  includes a plurality of DS storage units  36  (e.g., A, C, D, and F). In an example, where there are four pillars, there are four slices (X=4) created for each of Y data segments. Pillars can be allocated to more than one DS storage unit, but a given DS storage unit is not generally assigned to store more than one pillar from a given file/data object of a user vault to improve system robustness (e.g., avoiding loss of multiple slices of a data segment as a result of a single DS storage unit failure). 
     In an embodiment, one of the plurality of user virtual memories  152   a - n  utilizes a native OS file system to access the virtual DSN address space  148  by including source name information in requests such as read, write, modify, delete, list, etc. A vault identifier in the source name and/or a file/block name may be used to index the virtual DSN address space  148  to determine a user vault. A unique virtual vault is associated with each user (e.g., an individual, a group of individuals, a business entity, a group of business entities, etc.) and may contain operational parameters (described with more detail with respect to  FIG. 7 ), user attributes (e.g., user identification, billing data, etc.) and a list of DSN memories  22  and a plurality of storage units  36  for a DSN memory  22  that may be utilized to support the user. 
     In an example, the total virtual DSN address space  148  is defined by a forty-eight byte identifier thus creating 25648 possible slice names. The virtual DSN address space  148  accommodates addressing of EC data slices corresponding to segments of data objects (e.g., data file, blocks, streams) over various generations and vaults. The slice name is a virtual DSN address and remains the same even as different DS memories  22  or DS storage units  36  are added or deleted from the physical DSN memory  22 . 
     A user has a range of virtual DSN addresses assigned to their vault, user virtual memory  152   a - n . For instance, the virtual DSN addresses typically do not change over the operational lifespan of the system for the user. In another instance, the virtual DSN address space  148  is dynamically altered from time to time to provide such benefits as improved security and expansion, retraction, and/or capability. A virtual DSN address space  148  security algorithm may alter the virtual DSN address space  148  according to one or more of a command (e.g., from the DS managing unit  18 ), a schedule, a detected security breach, or any other trigger. The virtual DSN address may also be encrypted in use thus requiring encryption and decryption steps whenever the virtual DSN address is used. 
     The vault and file name index used to access the virtual DSN address space  148  and to create the slice names (virtual DSN addresses) may also be used as an index to access the virtual DSN address to physical location table  142 . For example, the virtual DSN address to physical location table  142  is sorted by vaults and pillars so that subsequent addresses are organized by pillar of the file data segments of a data object that have EC data slices with the same slice identifier and hence are typically stored at the same DS storage unit (e.g., slices having a first pillar identifier are stored in DS storage unit A of DSN memory  22 ). The output of the access to the virtual DSN address to physical location table  142  is the DSN memory identifier  154  and DS storage unit identifiers  156 . A source name, data segment header and/or slice name may include the DSN memory identifier  154  and/or DS storage unit identifiers  156 . 
     The slice names may be used as the virtual index to the memory system of each DS storage unit  36  of a particular DS memory  22  to gain access to the physical location of the EC data slices. In this instance, the DS storage unit  36  of the DS memory  22  maintains a local table correlating slice names (virtual DSN address) to the addresses of the physical media internal to the DS storage unit  36 . For example, user number 1 has a vault identified operational parameter of four pillars and pillar 0 is mapped to DS storage unit A of DSN memory  22 , pillar 1 is mapped to DS storage unit C of DSN memory  22 , pillar 2 is mapped to DS storage unit D of DSN memory  22 , and pillar 3 is mapped to DS storage unit F of DSN memory  22 . 
       FIG. 7  is a schematic block diagram of an embodiment of certain parameters associated with a user vault  200 . The parameters illustrated in  FIG. 7  may be stored in the user vault  200  or other resource, such as a user file, parameter database, file/block index, URL, etc. that is implemented in the managing unit  18 , DS processing unit  16  or a DS processing module  34 . 
     The operational parameters  202  include vault identifier field  204 , vault generation field  206 , error encoding scheme field  212 , slice number X field  214  (e.g., number of pillars n for the user vault) and threshold number T field  216 . The operational parameters  202  also include a fixed segment number Y field  208  and/or a Fixed Segment Size Field  210 . In an embodiment, the user vault  200  is configured with a Fixed Segment Size Field  210 . Since the data segment size is fixed, the number Y of data segments varies depending on the size of a data object. Padding or stuffing bytes may be added to one or more data segments to obtain the fixed segment size. In another embodiment, the user vault  200  is configured with a fixed segment number Y field  208 . Since the number of data segments is fixed, the size of the data segments varies depending on the size of a data object. In another embodiment, a user vault  200  may have varying configurations for different data objects. For example, some data objects are partitioned into a varying number Y of data segments with a fixed segment size while other data objects are partitioned into a fixed number Y of data segments with varying size. The operational parameters  202  associated with a user vault  200  shown in  FIG. 7  may also include other fields not described herein. 
     The user vault  200 , or other resource, such as a user file, parameter database, file/block index, URL, etc., also stores Files  220   a - n  with data segment information specific to data objects, including data segment size field  224 , data segment number Y field  226 , segment revision field  228 , data object size field  230  and segmentation strategy field  232 . In an example for a data object  40  having 4,194,304 bytes, when the Fixed Segment Size Field  210  specifies partitioning a data object  40  into fixed byte size segments of 4,096 bytes, then the data segment number field  224  specifies 1,024 data segments for the data object. Since the segment size is fixed, the File  220  for the data object may not include the data segment size field  226 . In another example for a data object  40  having 4,194,304 bytes, when the Fixed Segment Number Y Field  208  specifies Y=131,072, then the data segment size field  224  for the data object specifies 32 bytes. Since the segment number Y is fixed, the File  220  for the data object may not include the data segment number field  226 . The segment revision field  228  stores a revision number for the data object. The data object size field  230  stores a size of the data object, e.g. a number of bytes in the data object. The segmentation strategy field  232  stores whether the data object has a fixed number of data segments or a fixed segment size. 
     In an embodiment, one or more of the parameters in the File  220  may be included in the source name  35  for a data object or included in slice names  37  for a data segment or included in a data segment name or header. Other information not shown in  FIG. 7 , such as data object name, source name, file id, vault id, etc. associated with a data object may be stored as well in the user vault  200 . 
     In an embodiment, when a stored data object needs to be modified, a user device  12  and/or  14  sends a modification request to a DS processing module  34 , which authenticates the request. When the request is authenticated, the DS processing  34  reconstructs each of the plurality of data segments for the data object. It sends a read message to each of the DS storage units  36  storing at least a threshold number T of data slices for each of the plurality of data segments. The data slices are received for the plurality of data segments and the data segments are rebuilt therefrom. The DS processing  34  then reconstructs the data object from the plurality of rebuilt data segments and modifies the data object as per the modification request. However, this process of modification requires that each of the plurality of data segments is rebuilt and that in turn requires retrieving data slices for each data segment. 
       FIG. 8  is a flowchart illustrating another embodiment of a method  250  for modifying a stored data object  40  in the distributed storage network in accordance with the invention. In this embodiment, the DS processing module  34  only retrieves the data segments of the data object that require modification in response to the modification request. This embodiment improves response time and security by retrieving and rebuilding only a portion of the data object rather than the entire data object. In addition, only the rebuilt portion of the data object needs to be processed and stored after modification. 
     In operation, the DS processing module  34  identifies at least one of a plurality of data segments of a data object requiring modification in step  252 . The DS processing module  34  reconstructs the identified data segment from at least a threshold number T of the plurality of encoded data slices for the identified data segment to produce a reconstructed data segment in step  254 . The DS processing module  34  then modifies the reconstructed data segment to generate a modified data segment in step  256 . The modifications may include additions, deletions or revisions to one or more bytes of the reconstructed data segment. In an embodiment, the DS processing module  34  then generates a plurality of rebuilt encoded data slices from the modified data segment using the error encoding dispersal function and transmits the rebuilt encoded data slices for storage. 
       FIG. 9  is a logic flow diagram of an embodiment of a method  280  for identifying at least one of a plurality of data segments of a data object requiring modification. In an embodiment, in step  282 , the DS processing module  34  receives a request to modify a portion of a data object  40  from one of a user device  12 - 14 , DS processing unit  16 , DS managing unit  18 , storage integrity processing unit  20 , DSN memory or a DS unit  36 . In an embodiment, the modification request includes, inter alia, a user ID field, object name field and a position indicator and requested modifications. The position indicator includes an identification of or pointer to one or more bytes of the data object  40  for modification. For example, the position indicator may indicate byte 125,348 out of 2,465,820 bytes in the data object  40 . 
     The DS processing module  34  determines a segment size of the plurality of data segments of the data object in step  284 . In an embodiment, the DS processing module  34  accesses the user vault  200  to determine a data segment size for the data object  40 . When the operational parameters  202  for a user vault  200  indicate that data segments must have a fixed size, then the DS processing module  30  may only need to access the Fixed Segment Size Field  210  for the user vault  200 . When the user vault indicates data objects have a fixed segment number Y with varying sizes, then the DS Processing Module  34  may also need to access the data segment size field  224  for the data object in one of the Files  220   a - n . In an embodiment, the data segments of a data object may have varying sizes. For example, a first data segment includes 100,000 bytes and a second data segment includes 80,000 bytes, etc. In such a case, the DS processing module  34  must determine one or more sizes for the plurality of the data segments of the data object from the user vault  200 . In another embodiment, the modification request may include a data segment size for the plurality of data segments for the data object. 
     The DS processing module  34  in step  286  then identifies one or more data segments of the data object  40  requiring modification based on the position indicator and the data segment sizes. For example, when the data segment size is 100,000 bytes and the position indicator denotes byte 125,348, the DS processing module  34  identifies the second data segment of the data object  40  for modification because it includes the byte 125,348 that requires modification. Once the data segment is identified, the DS processing module  34  then determines a virtual DSN address of the encoded data slices for the identified data segment from the user virtual memory  152 , source name, data segment header, etc. and retrieves at least a threshold number T of the encoded data slices for the identified data segment from a DSN memory  22  based on the virtual DSN address to physical location table  142 . The DS processing module then reconstructs the identified data segment to generate a reconstructed data segment in step  288 . 
       FIG. 10  is a schematic block diagram of an embodiment of a modification request  300 . The modification request  300  includes a packet header  302  having for example, a user ID field  306 , object name field  308 , transaction type field  310 , source name field  312 , and payload length field  314 . The transaction type field  310  identifies the packet as a modification request. In operation, the DS processing module  34  processes the source name field  312  information in the modification request  300  to determine a vault identifier and to index the user vault  200 . When a source name is not available, the DS processing module  34  utilizes the user ID and object name to access the user virtual memory  152  to determine a vault identifier. The DS processing module then determines a virtual DSN address  148  for the data object from user virtual memory  152 . 
     The payload  304  of the modification request  300  includes one or more position indicator fields  316   a - n  and corresponding one or more modification fields  318   a - n . The position indicator field  316  includes an identification of or pointer to one or more bytes of the data object  40  for modification in accordance with the corresponding modification field  318 . The modification field  318  may include instructions for additions, deletions or revisions. 
       FIG. 11  is a logic flow diagram of an embodiment of a method  340  for modifying the reconstructed data segment. In step  342 , the DS processing module  34  modifies the reconstructed data segment in accordance with the modification request to generate a modified data segment. The modification may include changing one or more bytes of the data segment or deleting or adding one or more bytes. In an embodiment, the DS processing module  34  identifies and modifies more than one data segment when one or more bytes to be modified are included within more than one data segment. In step  344 , the data segment size field  224  in the user vault  200  or in a source name or packet header for the data segment is modified to update any changes to the data segment size. The segment revision field  228  in the user vault  200  or in a source name or packet header for the data segment is also updated in step  346 . 
       FIG. 12  is a logic flow diagram of another embodiment of a method  350  for modifying the reconstructed data segment. When modifications result in deleting or adding one or more bytes to a data segment or otherwise changing the data segment size in step  352 , the DS processing module  34  in step  354  determines whether the modified data segment size needs to be revised in step  354 . For example, the operational parameters  202  for the user vault  200  may require a fixed segment size or each of the plurality of data segments for the data object may each need to have a same data segment size, etc. When the segment size of the modified data segment does not need to be modified, the process continues to step  364  in which a data segment size field  224  is updated and then to step  366  in which a revision field is updated. 
     When the modified data segment size needs to be revised in step  354 , the DS processing module  34  determines whether it needs to increase or decrease the size of the modified data segment in step  356 . To increase the size of the modified data segment in step  358 , the DS processing module includes stuffing or padding bytes to the data segment. When the modified data segment size needs to decrease, the DS processing module  34  divides the modified data segment to generate at least two divided modified data segments in step  360 . The DS processing module  34  may then add stuffing or padding bytes to one or more of the divided data segments to reach the desired segment size, e.g., the fixed segment size or data segment size of the other plurality of data segments for the data object, etc. In step  362 , the DS processing module updates the Data Segment Number Y field  226  for the data object  40  in the user vault  200 . The DS processing module  30  also updates the data segment size field  224  in step  364 , and the revision field  228  for the data segment is updated to indicate a new number of total data object bytes in step  366 . 
     When modification is complete on a modified data segment (including any divided modified data segments), the DS processing module  34  encodes the modified data segment and slices it using an error encoding dispersal function based on the operational parameters in the user vault  200  to produce a number X of rebuilt encoded data slices. The DS processing module  34  generates a write request message to transmit the rebuilt encoded data slices to a DSN memory  22  for storage in a plurality of DS units  36 . 
       FIG. 13  illustrates a schematic block diagram of an embodiment of a write request message  380  having a protocol header  382  and a payload with one or more slice packets  384   a - n . A slice packet  384  includes a slice name field  388 , a slice revision field  390 , a slice length field  392 , and a slice payload field  394 . Each of the fields of a slice packet corresponds to the same encoded data slice. The slice name field  388  contains the slice name of the rebuilt encoded data slice while the slice revision field  390  contains a slice revision of the rebuilt encoded data slice. Since the rebuilt encoded data slice has been modified, the slice revision field is updated to reflect a new version. The slice length field  392  includes a slice length value representing a number of bytes of the rebuilt encoded data slice. The slice payload field  394  includes the bytes of the rebuilt encoded data slice. 
       FIG. 14  illustrates a logic flow diagram of an embodiment of a method  400  for generating and storing rebuilt encoded data slices from a modified data segment. As discussed, the DS processing module  34  encodes the modified data segment and slices it using an error encoding dispersal function based on the operational parameters in the user vault  200  to produce a plurality of rebuilt encoded data slices in step  402 . The DS processing module  34  generates a slice packet  384  for each of the plurality of rebuilt encoded data slices in step  404  and updates the slice name field  388 , slice revision field  390 , slice length field  392  and slice payload field  394  for each of the slice packets  384  in step  406 . The DS processing module  34  generates the protocol header and payload with the slice packets  384  to produce a write request message in step  408  and transmits the write request message to one or more DSN memories  22  for storage of the rebuilt encoded data slices in a plurality of storage units  36  in step  410 . The DS processing module  34  may update the virtual DSN address to physical location table  142  when there are any changes to the addressing of the rebuilt encoded data slices. 
       FIG. 15  is a schematic block diagram of an embodiment of a data segment header  412  for a data segment  42 . The data segment  412  includes a data object size field  230 , a fixed segment size field  210 , segmentation strategy field  232  and segment revision field  228 . The data segment header  412  may be included with a first of the plurality of data segments of the data object or included on each of the data segments. Additional or alternate fields may also be included in the data segment header  412 . 
       FIG. 16  is a flowchart illustrating another embodiment of a method  430  for modifying a data object stored in a DSN memory  22 . In an embodiment, the DS processing module  34  replaces an identified data segment without reconstructing it. For example, when a modification request includes modifications that would replace data for an entire identified data segment, then the identified data segment does not need to be reconstructed. Instead, a replacement data segment is generated and the identified data segment is replaced or overwritten by the replacement data segment. 
     In an embodiment, in step  432 , the DS processing module  34  receives a modification request  300  to modify a data object  40  from one of a user device  12 - 14 , DS processing unit  16 , DS managing unit  18 , storage integrity processing unit  20 , DSN memory or a DS unit  36 . The DS processing module  34  determines a segment size of the plurality of data segments of the data object in step  434 . The DS processing module  34  in step  436  then identifies one or more data segments of the data object  40  requiring modification based on the position indicator and the data segment size of the plurality of data segments to generate an identified data segment. In step  438 , the DS processing module  34  determines whether the identified data segment is replaced. For example, the requested modifications may include new data or revised data for the entire identified data segment. If so, a replacement data segment is generated from the data in the modification request in step  440 . The replacement data segment is then processed based on an error encoding dispersal function to generate a plurality of replacement data slices in step  440 . A segment revision  228  is updated for the replacement data segment in the user vault  200  or the data segment header  412 . The slice revision field  390  for the plurality of replacement data slices is also revised in step  442  though the replacement data slices will retain the same slice names as the stored data slices of the identified data segment. The DS processing module  34  then transmits the plurality of replacement data slices to the DSN memory  22  in step  446 . The plurality of data slices from the identified data segment are deleted and overwritten or replaced by the plurality of replacement data slices of the replacement data segment. 
     When a data segment is not replaced in step  438 , the identified data segment is reconstructed in step  448  and modified to generate a modified data segment in step  450  as described herein. 
     In an embodiment, the DS processing module  34  identifies and reconstructs one or more data segments of a data object that require modification in response to a modification request. Response time and security are improved because only a portion of the data object is processed for modification. 
       FIG. 17  is a logic flow diagram of an embodiment of a method  500  for updating software operating or stored on system elements of the distributed storage network. The system elements include devices or modules thereof operating in the distributed storage network, such as inter alia, user device  12 ,  14 , DS processing unit  16 , computing core  26 , interfaces  30 ,  32 ,  38 , DS managing unit  18 , storage integrity unit  20 , DSN memory  22 , and DS unit  36 . DS managing unit  18  determines whether a software update for one or more of the system elements is available in step  502 . A software update includes updates, fixes, patches, new applications, new versions of existing applications, or other modifications or additions to the software operating or stored on a system element. For example, the DS managing unit  18  determines whether a software update has been received over a network connection from another network node or a memory device (e.g., a disc, a USB memory stick, etc.) or whether a software update is available for download, such as from a network web server or other resource. 
     When available in step  504 , the DS managing unit  18  downloads or receives the software update and stores the software update in a repository memory. When the DS managing unit  18  determines that software updates are not currently available in step  504 , the DS managing unit  18  continues to determine whether a software update for one or more of the system elements is available. 
     In step  506 , the DS managing unit  18  determines whether any of the system elements require the software update. For example, the DS managing unit  18  may maintain a list of system elements and versions of software operating thereon. The DS managing unit  18  then compares the version of the software update to the version listed for the system elements. In another example, the DS managing unit  18  may determine whether the software update is optional, recommended or required. For example, the system elements may have a current version, not utilizing the applicable software, etc. When the DS managing unit  18  determines that the system elements do not currently require the software update in step  508 , the process continues back to step  502 . 
     When the DS managing unit  18  determines that the system elements do currently require the software update in step  508 , the DS managing unit identifies a system element to update in step  510  based on one or more factors. For example, the DS managing unit  18  may determine to install the software update first when it requires the update. In another example, a factor includes maintaining availability of at least a threshold number T of a storage set of DS units  36 . A storage set is the plurality of DS units  36  that store pillars for a user vault. Since the update process may take minutes or even hours, a limit on the number of DS units  36  that are unavailable due to a software update process may still enable a data object to be retrieved that is stored in the storage set. For example, at least a threshold number T of DS units  36  in a storage set need to be available to retrieve a data object. In another example, the DS managing unit  18  determines that at least a threshold number T plus a safety factor (e.g., one or two) of DS units  36  are available to enable the retrieval of data objects. In other words, the DS managing unit  18  will only update a number of DS units in the same storage set equal to [width n number of pillars−read threshold number T−safety factor]. For example, the DS managing unit  18  may concurrently update 4 DS units when n=16, read threshold T=10, and the safety factor=2. 
     The DS managing unit sends an activate process update client (PUC) message to the identified system element to initiate the software update process for that system element in step  512 . If additional system elements require the software update, the process continues to step  510  to identify a next system element to update. 
       FIG. 18  is a logic flow diagram of an embodiment of a method  520  for updating software operating or stored on a system element of the distributed storage network. In an embodiment, a system element installs a software update. The system element may have previously installed a process update client program which may be utilized to install and activate the software update. In step  522 , the system element determines whether it has received an activate process update client (PUC) message where the determination is based on comparing incoming commands from the network to that of the PUC command. When the system element determines that it has not received an activate process update client (PUC) message in step  524 , the process continues to step  522  to continue to scan for a PUC command. When the system element has received a PUC command, the system element activates the PUC and changes its status to unavailable in step  526 . The system element may complete critical steps in progress prior to changing the status and stop accepting new tasks. 
     The system element may suspend active processes in step  528  and save next steps in such suspended processes to execute later. The system element determines a location of the software update based on a local registry that may contain the network uniform resource identifier (URI) of the software repository and/or the URI of the DS managing unit  18  or other location. The system element accesses the URI and downloads the software update in step  530 . The system element installs the software update in step  532 . The software update should be backwards compatible with previous software versions to enable interactions with other system elements that have not installed the software update. The system element may activate one or more software installation and activation scripts included with the software update to perform an initialization in step  534 . When complete, the system element changes its status from unavailable to available, and it may complete earlier suspended tasks. 
     As may be used herein, the term(s) “coupled to” and/or “coupling” and/or includes direct coupling between items and/or indirect coupling between items via an intervening item (e.g., an item includes, but is not limited to, a component, an element, a circuit, and/or a module). As may further be used herein, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two items in the same manner as “coupled to”. As may even further be used herein, the term “operable to” indicates that an item includes one or more of power connections, input(s), output(s), etc., to perform one or more its corresponding functions and may further include inferred coupling to one or more other items. As may still further be used herein, the term “associated with”, includes direct and/or indirect coupling of separate items and/or one item being embedded within another item. 
     The present invention has also been described above with the aid of method steps illustrating the performance of specified functions and relationships thereof. The boundaries and sequence of these functional building blocks and method steps have been arbitrarily defined herein for convenience of description. Alternate boundaries and sequences can be defined so long as the specified functions and relationships are appropriately performed. Any such alternate boundaries or sequences are thus within the scope and spirit of the claimed invention. 
     The present invention has been described above with the aid of functional building blocks illustrating the performance of certain significant functions. The boundaries of these functional building blocks have been arbitrarily defined for convenience of description. Alternate boundaries could be defined as long as the certain significant functions are appropriately performed. Similarly, flow diagram blocks may also have been arbitrarily defined herein to illustrate certain significant functionality. To the extent used, the flow diagram block boundaries and sequence could have been defined otherwise and still perform the certain significant functionality. Such alternate definitions of both functional building blocks and flow diagram blocks and sequences are thus within the scope and spirit of the claimed invention. One of average skill in the art will also recognize that the functional building blocks, and other illustrative blocks, modules and components herein, can be implemented as illustrated or by discrete components, application specific integrated circuits, processors executing appropriate software and the like or any combination thereof.