Abstract:
A method begins by independently executing a first write transaction in a dispersed storage network (DSN) to a particular write verification step of a multiple step write process, wherein the first write transaction has a first transaction identifier. The method continues by independently executing a second write transaction in the DSN to the particular write verification step, wherein the second write transaction has a second transaction identifier, and wherein subject matter of the first write transaction is related to subject matter of the second write transaction. The method continues by dependently finalizing the multiple step write process for each of the first and second write transactions utilizing the first and second transaction identifiers when each of the first and second write transactions have reached the particular write verification step.

Description:
CROSS REFERENCE TO RELATED PATENTS 
       [0001]    The present U.S. Utility patent application claims priority pursuant to 35 U.S.C. §120 as a continuation of U.S. Utility application Ser. No. 12/903,205, entitled, “DIRECTORY SYNCHRONIZATION OF A DISPERSED STORAGE NETWORK,” filed Oct. 13, 2010, which is incorporated herein by reference in its entirety and made part of the present U.S. Utility patent application for all purposes. 
         [0002]    U.S. Utility patent application Ser. No. 12/903,205 claims priority pursuant to 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/290,775, entitled, “DISTRIBUTED STORAGE DATA SYNCHRONIZATION,” filed Dec. 29, 2009; and claims priority pursuant to 35 U.S.C. §120 as a continuation-in-part of U.S. Utility application Ser. No. 12/080,042, entitled, “REBUILDING DATA ON A DISPERSED STORAGE NETWORK,” filed Mar. 31, 2008. 
     
    
     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 
       [0003]    1. Technical Field of the Invention 
         [0004]    This invention relates generally to computing systems and more particularly to data storage solutions within such computing systems. 
         [0005]    2. Description of Related Art 
         [0006]    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. 
         [0007]    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.). 
         [0008]    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, which increases the demand on the storage function of computers. 
         [0009]    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.). 
         [0010]    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. 
         [0011]    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. 
         [0012]    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. 
         [0013]    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) 
         [0014]      FIG. 1  is a schematic block diagram of an embodiment of a computing system in accordance with the invention; 
           [0015]      FIG. 2  is a schematic block diagram of an embodiment of a computing core in accordance with the invention; 
           [0016]      FIG. 3  is a schematic block diagram of an embodiment of a distributed storage processing unit in accordance with the invention; 
           [0017]      FIG. 4  is a schematic block diagram of an embodiment of a grid module in accordance with the invention; 
           [0018]      FIG. 5  is a diagram of an example embodiment of error coded data slice creation in accordance with the invention; 
           [0019]      FIG. 6  is another schematic block diagram of another embodiment of a computing system in accordance with the invention; 
           [0020]      FIG. 7  is another schematic block diagram of another embodiment of a computing system in accordance with the invention; 
           [0021]      FIG. 8  is another schematic block diagram of another embodiment of a computing system in accordance with the invention; 
           [0022]      FIG. 9  is a flowchart illustrating an example of selecting a dispersed storage (DS) processing unit in accordance with the invention; 
           [0023]      FIG. 10A  is another schematic block diagram of another embodiment of a computing system in accordance with the invention; 
           [0024]      FIG. 10B  is another schematic block diagram of another embodiment of a computing system in accordance with the invention; 
           [0025]      FIG. 11  is a flowchart illustrating an example of determining a dispersed storage (DS) unit storage set in accordance with the invention; 
           [0026]      FIG. 12A  is a schematic block diagram of an embodiment of a dispersed storage network (DSN) memory in accordance with the invention; 
           [0027]      FIG. 12B  is another schematic block diagram of another embodiment of a dispersed storage network (DSN) memory in accordance with the invention; 
           [0028]      FIG. 13  is another schematic block diagram of another embodiment of a computing system in accordance with the invention; 
           [0029]      FIG. 14  is a flowchart illustrating an example of storing data in accordance with the invention; 
           [0030]      FIG. 15  is a flowchart illustrating an example of retrieving data in accordance with the invention; 
           [0031]      FIG. 16  is another flowchart illustrating another example of storing data in accordance with the invention; and 
           [0032]      FIG. 17  is a flowchart illustrating an example of storing an encoded data slice in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]      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). 
         [0034]    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. 1-17 . 
         [0035]    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  33 . An embodiment of the computing core  26  will be described with reference to  FIG. 2 . 
         [0036]    With respect to the interfaces, each of the interfaces  30 ,  32 , and  33  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  33  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 . 
         [0037]    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. 
         [0038]    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). 
         [0039]    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. 
         [0040]    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 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. 
         [0041]    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 . 
         [0042]    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. 
         [0043]    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 file  38  and/or data block  40  to store in the DSN memory  22 , it sends the data file  38  and/or data block  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 file  38  and/or data block  40 . 
         [0044]    The DS processing unit  16  receives the data file  38  and/or data block  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 file  38  and/or data block  40  into one or more data segments, which is represented as Y data segments. For example, the DS processing  34  may partition the data file  38  and/or data block  40  into a fixed byte size segment (e.g., 2 1  to 2 n  bytes, where n=&gt;2) or a variable byte size (e.g., change byte size from segment to segment, or from groups of segments to groups of segments, etc.). 
         [0045]    For each of the Y data segments, 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 segment into a plurality of error coded (EC) data slices  42 - 48 , which is 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 n/k system, then a data segment is divided into n slices, where k number of slices is needed to reconstruct the original data (i.e., k is the threshold). As a few specific examples, the n/k factor may be 5/3; 6/4; 8/6; 8/5; 16/10. 
         [0046]    For each EC slice  42 - 48 , the DS processing unit  16  creates a unique slice name and appends it to the corresponding EC slice  42 - 48 . 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.). 
         [0047]    The DS processing unit  16  transmits the plurality of EC slices  42 - 48  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 EC slices  42 - 48  for transmission via the network  24 . 
         [0048]    The number of DS units  36  receiving the EC slices  42 - 48  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 of each of the data segments is to be stored in a first DS unit  36 , the second slice of each of the data segments 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. 2-17 . 
         [0049]    Each DS unit  36  that receives an EC slice  42 - 48  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. 
         [0050]    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 . 
         [0051]    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. 
         [0052]    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 . 
         [0053]    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 the data file  38  and/or data block  40  to the user device  14 . Note that the first type of user device  12  performs a similar process to retrieve a data file and/or data block. 
         [0054]    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  45 , and/or slice names, of a data file or data block of a user device 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. 
         [0055]    If the storage integrity processing unit  20  determines that one or more slices 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 rebuild slice, or slices, in the appropriate DS unit(s)  36  in a manner that mimics the write process previously described. 
         [0056]      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 , an IO interface  60 , at least one IO 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. 
         [0057]    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. 1-17 . 
         [0058]      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 the DSnet interface  32  or the interfaces  68  and/or  70  may be part of user device  12  or of the DS processing unit  16 . 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. 
         [0059]    In an example of storing data, the gateway module  78  receives an incoming data object that includes a user ID field  86 , an object name field  88 , and the data object field  40  and may also receive corresponding information that includes 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. 
         [0060]    When the user is authenticated, the gateway module  78  obtains user information from the management unit  18 , the user device, 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. 
         [0061]    The gateway module  78  uses the user information to assign a source name  35  to the data. 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. 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. 
         [0062]    The access module  80  receives the data object  40  and creates a series of data segments  1  through Y  90 - 92  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 of segments Y may be chosen or randomly assigned based on a selected segment size and the size of the data object. For example, if the number 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, if segment sized 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 size of each segment is 4,096 bytes, the then number of segments Y=1,024. Note that each segment is associated with the same source name. 
         [0063]    The grid module  82  receives the 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 . 
         [0064]    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-free 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 is greater than or equal to the read threshold for a given number of pillars (X). 
         [0065]    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 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). 
         [0066]    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. 
         [0067]    When the error coded data slices of a data segment are ready to be outputted, 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 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  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 . 
         [0068]    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  82 . The storage module  84  then outputs the encoded data slices  1  through X of each segment  1  through Y to the DS storage units  36 . 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. 
         [0069]    In an example of a read operation, the user device  12  and/or  14  sends a read request to the DS processing unit  16 , which authenticates the request. When the request is authentic, the DS processing unit  16  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 DSnet 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 was 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. 
         [0070]      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. 
         [0071]    In an example of write operation, the pre-slice manipulator  75  receives a data segment  90 - 92  and a write instruction from an authorized user device. The pre-slice manipulator  75  determines if pre-manipulation of the data segment  90 - 92  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. 
         [0072]    Once a positive determination is made, the pre-slice manipulator  75  manipulates the data segment  90 - 92  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. 
         [0073]    The encoder  77  encodes the pre-manipulated data segment  92  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  92  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  92 , the same encoding algorithm for the data segments  92  of a data object, or a combination thereof. 
         [0074]    The encoded data segment  94  is of greater size than the data segment  92  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  92 . For example, if X=16 and T=10, then the data segment  92  will be recoverable as long as 10 or more EC data slices per segment are not corrupted. 
         [0075]    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  92 . For example, if the slicing parameter is X=16, then the slicer  79  slices each encoded data segment  94  into 16 encoded slices. 
         [0076]    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. 
         [0077]    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  90 - 92 . The pre-slice de-manipulator  83  performs the inverse function of the pre-slice manipulator  75  to recapture the data segment  90 - 92 . 
         [0078]      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  94  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). 
         [0079]      FIG. 6  is another schematic block diagram of another embodiment of a computing system. As illustrated, the system includes a plurality of user devices  14 , a network  24 , a dispersed storage (DS) processing unit  16 , and a dispersed storage network (DSN) memory  22 . Note that the DSN memory  22  may be operably coupled to the DS processing unit  16  directly or via the network  24 . As illustrated, the DS processing unit  16  includes a DS processing  34  and a plurality of functional layers to enable the DS processing  34  to interface with the plurality of user devices  14 . As illustrated, functional layers interface with other functional layers above and below the functional layer converting one set of protocols and/or procedures to the next as discussed in more detail below. 
         [0080]    As illustrated, there are at least two primary methods to interface the plurality of user devices  14  to the DS processing  34 . A first primary method is an object method and a second primary method is a block method. In the object method, data is interchanged in the form of an object that may have variable size, name(s), directory links, and metadata. Object storage includes a sequence of bytes of a varying length to help abstract the physical storage (e.g., object names rather than just disk drive locations). User devices can add/delete bytes of an object. The object may have attached metadata describing the data. This layer looks like an object storage device to the above layers. For example, different size files and/or data associated with a client/server application. In the block method, data is interchanged in the form of fixed length blocks. Block storage utilizes a sequence of bytes of a nominal length to help abstract the physical storage (e.g., block numbers rather than just disk drive locations). Files may be converted to blocks such that files typically fill multiple blocks. The block storage system can be abstracted by a file system for the user device. 
         [0081]    Within the object method there are at least two secondary interfacing methods. A first secondary method is a simple object method and a second secondary method is a file system method. In the simple object method, data is interchanged that may not conform to a typical computer file and directory system. Simple objects include data without a file structure such as bytes exchanged in an embedded client with a server application. Simple objects may be communicated in messages via HTTP. Simple objects may utilize simple object access protocol (SOAP) procedures to exchange extensible markup language (XML) style documents. For example, location data exchanged between a global positioning system (GPS) equipped user device and a location services application server. In the file system method, an approach is provided for storing and organizing data where the data is interchanged conforming to a typical computer file and directory system. In the file system, file names are assigned to files and organized in a directory. File name may be an index into a file allocation table (FAT) of location information. For example, a user device sends a Windows formatted file to the DSN system. 
         [0082]    As illustrated, the DS processing unit  16  interfaces the DSN memory  22  to the plurality of user devices  14  through either an object layer  142  and/or a block layer  144 . The object layer  142  interfaces with either a simple object layer  132  and/or a file system layer  138 . As illustrated, the simple object layer  142  interfaces with either a Java SDK (software developer kit) layer  114  and/or a web service layer  132 . In an example, the Java SDK layer  114  may utilize a loader to interpret Java class files generated by a Java compiler. For instance, a Java archiver may manage Java Archive (JAR) files. In an example, the web service layer  132  utilizes a protocol for machine to machine interaction over a network. For instance, the protocol includes a simple object access protocol (SOAP) standard over hypertext protocol (HTTP) or representational state transfer (REST). The web service layer  132  interfaces with a HTTP/REST API layer  116 . In example, the REST API layer on  16  utilizes a client server approach with discrete states without a continuous server load (e.g., a request followed by a response with no state maintained by a server). Note that REST may run over HTTP. 
         [0083]    As illustrated, the file system layer  138  interfaces with either a FTP (file transfer protocol) layer  118 , an AFP (Apple Filing Protocol) layer  120 , and/or a Web DAV (web based distributed authoring and versioning) layer  122 . In example, the FTP layer  118  is utilized to exchange files over transport control protocol/internet protocol (TCP/IP) such as the internet via ports. For instance, FTP utilizes a client server approach. For instance, FTP may utilize separate control and data streams and applications may be command line or graphical. Note that a secure sockets layer (SSL) and/or transport layer security (TLS) may be added for improved security. In an example, the AFP layer  120  provides a network protocol of file services for the Macintosh operating system (OS) family over TCP/IP. In an example, the Web DAV layer  122  provides extensions to HTTP to allow the plurality of user devices  14  to create, change, and/or move files on a web server. For instance, Windows OS provides directory web folders. 
         [0084]    As illustrated, the block layer of  44  interfaces with a SCSI (small computer system interface) layer  140 . In an example, the SCSI layer  140  provides a bus approach physical connection and data transfer between computers and peripheral devices. For instance, SCSI enables initiators (e.g., in user device) to send commands to targets (e.g., in DS processing unit and/or DS memory). The SCSI layer  140  interfaces with an iSCSI (internet small computer system interface) layer  134 . In an example, the iSCSI layer  134  transfers SCSI commands over the internet and/or the network  24  via TCP/IP enabling remote initiators (e.g., in user device  14 ) to send commands to targets (e.g., in DS processing unit  16  and/or DS unit  36 ). 
         [0085]    As illustrated, the iSCSI layer  134  interfaces with a NFS (network file system) layer  124 , a FTP layer  126 , an AFP layer  128 , a CIFS (common internet file system) layer  130 , and/or directly with the user device  14 . In example, the NFS layer  124  enables user devices access over a network  24  where the DS processing unit  16  implements a NFS daemon process to make data available to a plurality of user devices  14 . For instance, directories are communicated as user device  14  requests a mount. In an example, the CIFS layer  130  provides a client server application layer network protocol to provide shared access to files, printers, serial ports (e.g., common in Windows OS). The FTP layer  126  and AFP layer  128  function as previously discussed. 
         [0086]    In an example of operation, the user device  14  utilizes an embedded interface  102  to store data  108  in the DSN memory  22 . A user device data application communicates REST transfers via HTTP over the network to the HTTP/REST API interface layer  116 . The web service layer  132  may host the server side of the REST transfers. The object layer  142  interfaces the data to the DS processing  34  where the data is segmented, encoded, and sliced in accordance with an error coded dispersal storage function to produce encoded data slices  11 . The DS processing  34  sends the encoded data slices  11  to the DSN memory  22  for storage therein. 
         [0087]    In another example of operation, the user device  14  utilizes a URL interface (uniform resource locator)  104  to store a file  110  in the DSN memory  22 . A user device file application communicates Web DAV transfers via HTTP over the network  24  to the Web DAV interface layer  122 . The Web DAV interface  122  may provide web folders to the user device  14  such that the user device  14  may drop the file  110  to be stored in the DSN memory  22  into the folder. The file system layer  138  and the object layer  142  interfaces data of the file  110  to the DS processing  34  where the data is segmented, encoded, and sliced in accordance with an error coded dispersal storage function to produce encoded data slices  11 . The DS processing  34  sends the encoded data slices  11  to the DSN memory  22  for storage therein. 
         [0088]    In another example of operation, the user device  14  utilizes a hard drive style interface to store data blocks  112  in the DSN memory  22 . A user device block application communicates CIFS transfers over the network  24  to the CIFS interface layer  130 . The CIFS interface layer  130  may provide shared access to the user device  14  such that the user device when  14  looks at the DSN memory  22  as an iSCI device to store data blocks  112  in the DSN memory  22 . The iSCSI  134  and SCSI layer  140  interfaces data of the data blocks  112  to the DS processing  34  where the data is segmented, encoded, and sliced in accordance with an error coded dispersal storage function to produce encoded data slices  11 . The DS processing  34  sends the encoded data slices  11  to the DSN memory  22  for storage therein. 
         [0089]      FIG. 7  is another schematic block diagram of another embodiment of a computing system. As illustrated, the system includes a user device  12 , a network  24 , and a DSN memory  22 . As illustrated, the user device  12  includes a plurality of functional layers including a DS processing  34  where the DS processing  34  interfaces with the DSN memory  22  and a plurality of interfacing functions  114 - 144  that interface with a plurality of applications  146 - 150 . The interfacing functions  114 - 144  operate as discussed with reference to  FIG. 6 . 
         [0090]    There are at least two primary interfacing methods from the DS processing  34  to the applications  146 - 150 . A first primary method is an object method and a second primary method is a block method as previously discussed with reference to  FIG. 6 . As illustrated, a data application  146  interfaces with the Java SDK layer  114  and/or HTTP/REST API layer  116  interfacing functions. As illustrated, a file application  148  interfaces with a FTP layer  118 , an AFP layer  120 , and/or a Web DAV layer  122  interfacing functions. As illustrated, a block application  150  interfaces with a NFS layer  124 , a FTP layer  126 , an AFP layer  128 , a CIFS layer  130 , and/or directly with an iSCSI layer  134 . In another example, the applications  146 - 150  may interface directly with one or more of a web service layer  132 , a simple object layer  136 , a file system layer  138 , the iSCSI layer  134 , an object layer  142 , and a block layer  144 . 
         [0091]    The applications  146 - 150  may utilize protocols (e.g., above the physical layer) of the interfacing functions  114 - 144  to access the DSN memory  22 . The data application  146  communicates data with the DS processing  34  to access the DSN memory  22 . The file application  148  communicates files with the DS processing  34  to access the DSN memory  22 . The block application  150  communicates data blocks with the DS processing  34  to access the DSN memory  22 . The DS processing sends slices  11  through the network  24  to the DSN memory  22  for storage therein. The DS processing  34  retrieves slices  11  from the DSN memory  22  through the network  24 . 
         [0092]      FIG. 8  is another schematic block diagram of another embodiment of a computing system. As illustrated, the system includes a plurality of user devices  1 - u , a plurality of DS processing units  1 - p , and a DSN memory  22 . In an example of operation, the user device  1  may determine a DS processing unit  3  to utilize based on matching DS processing unit attributes to DS processing unit requirements. In another example, user device  2  determines to utilize DS processing unit  3  when DS processing unit  3  has the most favorable availability history of the plurality of DS processing units  1 - p  and DS processing unit  3  is expected to continue to be available at a level that compares favorably with the user device  2  DS processing unit requirements. 
         [0093]    In another example of operation, the user device  6  may determine a DS processing unit  5  to utilize based on a predetermination and/or initially on a predetermination followed by a potential subsequent modification based in part on actual performance. In another example, user device  3  determines to initially utilize DS processing unit  1  when DS processing unit  1  is listed in a predetermined table. Next, user device  3  determines to subsequently utilize DS processing unit  2  when DS processing unit  1  does not perform to a required level and DS processing unit  2  is the second choice. 
         [0094]    In an example of operation, user device  7  provides DSN memory access authorization credentials when accessing the DSN memory  22  via DS processing unit  10 . Next, the DS processing unit  10  verifies the authorization credentials. The DS processing unit  10  forwards a DSN memory access request to the DSN memory  22  when the authorization credential verification is favorable (e.g., on a list of authorized users for the particular item in the DSN memory  22 ). The DS processing unit  10  does not forward a DSN memory access request to the DSN memory  22  when the authorization credential verification is not favorable (e.g., not on a list of authorized users for the particular item in the DSN memory  22 ). The method of operation of the user device  1 - u  to determine the DS processing unit  1 - p  is discussed in greater detail with reference to  FIG. 9 . 
         [0095]    In another sample, DS processing unit  3  forwards the authorization credentials to the DSN memory  22  with the DSN memory access request (e.g., without verification by the DS processing unit  3 ). The DSN memory  22  verifies the authorization credentials. The DSN memory  22  processes the memory access request when the authorization credential verification is favorable. The DSN memory  22  does not process the memory access request when the authorization credential verification is not favorable. 
         [0096]      FIG. 9  is a flowchart illustrating an example of selecting a dispersed storage (DS) processing unit. The method begins at step  152  where a processing module (e.g., of a user device) determines dispersed storage network (DSN) memory access requirements. The requirements may include one or more of security requirements, performance requirements, and priority requirements. Such a determination may be based on one or more of a query, a data type, a data size, a security indicator, a performance indicator, a command, a predetermination, and a lookup. 
         [0097]    The method continues at step  154  where the processing module determines candidate DS processing units based on one or more of a virtual DSN address to physical location table, a query, a message from one or more DS processing units, a data type, a data size, a security indicator, a performance indicator, a status indicator, a command, a predetermination, and a lookup. The method continues at step  156  where the processing module determines candidate DS processing units attributes where the attributes may include one or more of current capacity, current loading, uptime history, performance history, data types supported, data types not supported, security restrictions, and encryption algorithms supported. Such a determination may be based on one or more of a virtual DSN address to physical location table, a query, a message from one or more DS processing units, a data type, a data size, a security indicator, a performance indicator, a command, a predetermination, and a lookup. In an example, the processing module determines that DS processing unit  1  has an attribute of capacity above a threshold based on the performance indicator. In another example, the processing module determines that DS processing unit  4  has an attribute of a particular encryption algorithm based on the security indicator from a query. 
         [0098]    The method continues at step  158  where the processing module determines a DS processing unit to utilize based on one or more of the DSN access requirements, the candidate DS processing units, the candidate processing units attributes, a comparison of the candidate processing units attributes to the DSN access requirements, a virtual DSN address to physical location table, a query, a message from one or more DS processing units, a data type, a data size, a security indicator, a performance indicator, a command, a predetermination, and a lookup. In an example, the processing module determines the DS processing unit such that substantially all of the requirements are met or exceeded. For instance, the processing module determines the DS processing unit that meets or exceeds the most requirements. The method continues at step  160  where the processing module utilizes the determined DS processing unit for the DSN access (e.g., store, retrieve, delete, check status). 
         [0099]      FIG. 10A  is another schematic block diagram of another embodiment of a computing system and  FIG. 10B  is another schematic block diagram of another embodiment of a computing system. As illustrated in  FIG. 10A , the system includes a user device  14 , a dispersed storage (DS) processing unit  16 , and a dispersed storage network (DSN) memory storage set  1 . The system of  FIG. 10B  includes the user device  14 , the DS processing unit  16 , the DSN memory storage set  1 , and a DSN memory storage set  2  (e.g., to affect capacity expansion). As illustrated, the DSN memory storage sets  1  and  2  include a plurality of dispersed storage (DS) units  1 - 4  to accommodate a vault with a pillar width n=4. For instance, pillar  1  slices are stored in DS unit  1 , pillar  2  slices are stored in DS unit  2 , pillar  3  slices are stored in DS unit  3 , and pillar  4  slices are stored in DS unit  4 . Note that the DSN memory storage sets  1  and  2  may include any number of DS units. 
         [0100]    In an example of operation, the DS processing unit  16  determines if memory utilization of DSN memory storage set  1  is above a threshold (e.g., when the memory utilization is greater than or equal to 70% utilized). Such a determination may be based on one or more of a query of one or more of the DS units  1 - 4  of the DSN memory storage set  1 , a message from a DS managing unit, and/or a message from the DSN memory storage set  1 . Next, the DS processing unit  16  sends a memory utilization alert to the DS managing unit when the DS processing unit  16  determines that the memory utilization is above the threshold. In addition, the DS processing unit  16  may activate a dormant DSN memory storage set as DSN memory storage set  2  to provide more storage capacity for at least one vault that is utilizing DSN memory storage set  1 . 
         [0101]    In another example of operation, the DS processing unit  16  determines which of the two storage sets to utilize when the DS processing unit  16  has new data to send to the DSN memory for storage. As illustrated in  FIG. 10B , DSN memory storage set  2  has the same number of DS units as DSN memory storage set  1 . In another example, DSN memory storage set  2  may include two or more DS units for each pillar. 
         [0102]    In another example of operation, the DS processing unit  16  determines to send pillar  1  slices to DS unit  1  of DSN memory storage set  2 . In another example, the DS processing unit  16  determines to send pillar  1  slices to DS unit  1  of DSN memory storage set  1 . Note that DSN memory storage set  1  may be nearly full while DSN memory storage set  2  may be nearly empty. In another example of operation, the DS processing unit  16  balances distribution of new data between the two DSN memory storage sets to achieve a balancing objective. For instance, the balancing objective may include completely filling DSN memory storage set  1  followed by sending subsequent data to DSN memory storage set  2 . In another instance, the balancing objective may include alternating sending new data to the DSN memory storage sets such that DSN memory storage set  1  fills up to capacity first. In yet another instance, the balancing objective may include alternating sending new data to the DSN memory storage sets such that the DSN memory storage sets fill up to capacity substantially simultaneously. The DS processing method to balance the utilization is discussed in greater detail with reference to  FIG. 11 . 
         [0103]      FIG. 11  is a flowchart illustrating an example of determining a dispersed storage (DS) unit storage set. The method begins at step  162  where a processing module (e.g., of one of a dispersed storage (DS) processing unit, a user device, a dispersed storage (DS) managing unit, a storage integrity processing unit, or a dispersed storage (DS) unit) receives a store data object message (e.g., from one of the user device, the DS processing unit, the DS managing unit, the storage integrity processing unit, or the DS unit). Such a store data object message may include one or more of a data object, a command, a user ID, a data object name, a data type, a data size, a priority indicator, a security indicator, a performance indicator, and other metadata. 
         [0104]    The method continues at step  164  where the processing module determines operational parameters based on one or more of the data object, a vault lookup, a query of dispersed storage network (DSN) memory storage set memory utilization, a command, a user ID, a data object name, a data type, a data size, a priority indicator, a security indicator, a performance indicator, and other metadata. For example, the processing module determines that the pillar width is four based on the user ID. The method continues at step  166  where the processing module determines available DSN memory storage set(s) based on one or more of a query, the operational parameters, a vault lookup, a predetermination, a query of DSN memory storage set memory utilization, a command, a user ID, a data object name, a data type, a data size, a priority indicator, a security indicator, a performance indicator, and other metadata. For example, the processing module determines that DSN memory storage sets  1  and  2  are available based on a query. 
         [0105]    The method continues at step  168  where the processing module determines a DSN memory storage set to utilize based on one or more of the available storage set(s), a balancing objective, a query, the operational parameters, a vault lookup, a predetermination, a random number, a query of DSN memory storage set memory utilization, a command, a user ID, a data object name, a data type, a data size, a priority indicator, a security indicator, a performance indicator, and other metadata. In an example, the processing module determines that the balancing objective is to alternate sending new data to the available DSN memory storage sets such that the DSN memory storage sets fill up to capacity substantially simultaneously and that available DSN memory storage set  1  has 30% capacity remaining and DSN memory storage set  2  has 95% capacity remaining. For instance, the processing module determines a random number from 1 to 125 (e.g., 30+95=125). Next, the processing module encodes the data object in accordance with an error coding dispersal storage function to produce encoded data slices. The processing module sends the encoded data slices to DSN memory storage set  1  for storage therein when the random number is less than or equal to 30. The processing module sends the encoded data slices to DSN memory storage set  2  for storage therein when the random number is greater than 30. Note that this weighted method balances the utilization to meet the balancing objective. 
         [0106]      FIG. 12A  is a schematic block diagram of an embodiment of a dispersed storage network (DSN) memory and  FIG. 12B  is another schematic block diagram of another embodiment of a dispersed storage network (DSN) memory. As illustrated in  FIG. 12A , the DSN memory includes a dispersed storage (DS) unit  1  at site  1 . As illustrated, DS unit  1  includes a storage unit control module  170  and a plurality of memories  1 - 12 . The storage unit control module  170  may be implemented with the computing core  26  of  FIG. 2 . The memories  1 - 12  may be implemented by one or more of a magnetic hard disk, NAND flash, read only memory, optical disk, and/or any other type of read-only, or read/write memory. The memories may be implemented as part of or outside of the DS unit  1 . For example, memories  1 - 4  may be implemented in the DS unit  1  and memories  5 - 12  may be implemented in a remote server (e.g., a different DS unit operably coupled to the DS unit  1  via the network  24 ). In another example, memories  1 - 8  are implemented with the magnetic hard disk technology and memories  9 - 12  are implemented with the NAND flash technology. 
         [0107]    As illustrated in  FIG. 12B , the DSN memory includes the DS unit  1  at site  1  and a DS unit  2  at site  2  at a time subsequent to that of  FIG. 12A . As illustrated, DS unit  1  includes the storage and control module  170  and memories  1 - 6 . As illustrated, DS unit  2  includes the storage unit control module  170  and memories  7 - 12 . Note that memories  1 - 12  are transportable such that memories  7 - 12  were transferred to DS unit  2  while memories  1 - 6  remain in DS unit  1 . 
         [0108]    As illustrated, the storage unit control module  170  is operably coupled to the computing system via the network  24 . The storage unit control module  24  may include DS processing  34  and may receive, via the network, a store command, metadata, and a data object to store. Note that the DS unit access may be via a WebDAV sequence, e.g., via an IP address such as http://21.8.44/vault1 to facilitate easy DS unit access. The data object may include a simple object file, a block file, and/or EC data slices. In an example, the storage unit control module  170  stores the data object in one or more of the memories  1 - 12  substantially as received (e.g., a slice is stored as a slice, a block file is stored as a block file, etc.). In another example, the storage unit control module  170  encodes the data object utilizing an error coding dispersal storage function to produce encoded data slices and stores the encoded data slices in one or more of the memories  1 - 12 . Note that the storage unit control module unit may determine to utilize only the memories  1 - 12  of the DS unit  1  when the capabilities of memories  1 - 12  substantially meet the requirements. In another example, the storage unit control module  170  determines to utilize some combination of the memories  1 - 12  of the DS unit and memory of at least one other DS unit when the capabilities of memories  1 - 12  alone substantially do not meet the requirements. 
         [0109]    In an example of operation, the storage unit control module  170  determines where (e.g., which address of one or more of the memories) to store the received data object as encoded data slices. Such a determination may be based on one or more of metadata, a command (e.g., from the DS processing unit indicating which memory or memory type to use), a type of data indicator, a local virtual DSN address to physical location table lookup, a priority indicator, a security indicator, available memory, memory performance data, memory status, memory cost data, and any other parameter to facilitate desired levels of efficiency and performance. For instance, the storage unit control module  170  may select memories  1 - 12  (e.g., magnetic hard disk drives) to store the encoded data slices since the performance and efficiency is good enough for the requirements (e.g., availability, cost, response time). In another instance, the storage unit control module  170  distributes the slices to memories  1 - 10  when memories  11  and  12  are not available. In another instance, the storage unit control module  170  distributes the slices at various addresses across one memory. In another instance, the storage unit control module  170  distributes a read threshold k=8 of the encoded data slices across memories  1 - 8  (for fast retrieval) and the other 4 (n-k) encoded data slices to other DS units. In yet another instance, the storage unit control module  170  distributes the encoded data slices across the DS unit memories and at least one other DS unit at the same site as the DS unit  1 . In yet another instance, the storage unit control module  170  distributes the encoded data slices across the DS unit memories and at least one other DS unit at a different site as the DS unit  1 . 
         [0110]    In a further example of operation, the storage unit control module  170  creates and maintains a local virtual DSN address to physical memory table. The storage unit control module  170  determines where previously stored encoded data slices are located based on the local virtual DSN address to physical memory table upon receiving a retrieve request via the network  24 . Note that a DS processing unit operably coupled to the DS unit  1  via the network, maintains a virtual DSN address to physical memory table for the system tracking where the pillars are located for each vault. 
         [0111]    In the example of operation, the storage unit control module  170  determines when a change has occurred to the memory configuration of the DS unit  1  and updates the local virtual DSN address to physical memory table (e.g., DS unit level) and sends a configuration update message to the DS processing unit to update the virtual DSN address to physical memory table (e.g., system level) based on the memory configuration change. The storage unit control module  170  determines when a change has occurred to the memory configuration of the DS unit  1  based on one or more of a configuration message from the DS managing unit, a memory query, a test, an error message, a configuration indicator, a command, a vault lookup, a command, a predetermination, and a DS unit message. For instance, the storage unit control module  170  of DS unit  1  in  FIG. 12B  determines that a change (e.g., memory  7 - 12  has been removed, which is utilized to store pillars  7 - 12  of vault  301 ) has occurred based on a query of the memories  1 - 12 . 
         [0112]    In another instance, any number of pillars may be moved (e.g., via memory transport) from one DS unit to another. In another instance, the storage unit control module  170  of DS unit  2  in  FIG. 12B  determines that a change (e.g., memory  7 - 12  has been added which holds slices from pillars  7 - 12  of vault  301 ) has occurred based on a query of the memories  1 - 12  and a DS managing unit configuration message. Next, storage unit control module  170  of DS unit  1  in  FIG. 12B  updates its associated local DSN address to physical location table and send a configuration update message to the DS processing unit where the message includes an indication that pillars  1 - 6  (e.g., of a vault  301 ) are stored in DS unit  1  and/or pillars  7 - 12  are not stored in DS unit  1 . The storage unit control module  170  of DS unit  2  in  FIG. 12B  updates its associated local DSN address to physical location table and send a configuration update message to the DS processing unit where the message includes an indication that pillars  7 - 12  (e.g., of vault  301 ) are stored in DS unit  2 . The DS processing unit utilizes the DS units to access the pillars of the new configuration. The DS units provide slice access for the pillars of the new configuration. 
         [0113]      FIG. 13  is another schematic block diagram of another embodiment of a computing system. As illustrated, the system includes a processing module  50  (e.g., hosting the file application), a data object cache  172 , a DS processing  34 , and a dispersed storage network (DSN) memory  22 . In an implementation embodiment, the processing module  50 , data object cache  172 , and DS processing  34  may be implemented as part of a user device  12 . In another implementation embodiment, the processing module  50  and data object cache  172  may be implemented as part of a user device  12  and the DS processing  34  may be implemented as part of a DS processing unit  16 . 
         [0114]    The processing module  50  may be part of the computing core  26  of  FIG. 2  and may include memory to run a file application and store a working copy of a file. The processing module  50  may host a file application, which during a first timeframe manipulates a first portion of the file. In an example, the manipulation may include one or more of reading, editing, deleting, moving, inserting, replicating, and checking status. The file application may manipulate a second portion of the file during a second timeframe etc. 
         [0115]    The data object cache  172  may comprise memory to temporarily store at least a portion of the file. The contents of the data object cache  172  may change frequently as the file is manipulated. The file may be deleted from the data object cache  172  once the manipulation sequences conclude. Portions of the file may be stored as slices  11  in the DSN memory  22  from time to time. 
         [0116]    In an example of operation, DS processing  34  stores and/or retrieves slices  11  of the file in the DSN memory  22 . For instance, the DS processing  34  determines to select at least a portion of the file, segment the portion, encode, and slice the portion to produce encoded data slices in accordance with an error coding dispersal storage function. Next, the DS processing  34  send the encoded data slices to the DSN memory  22  for storage therein. In another instance, the DS processing  34  moves the portion of the file from the processing module  50  to the data object cache  172 . The determination to save the portion in DSN memory  22  may be based on one or more of an action policy (e.g., when the file has changed), a query for change, a message from the processing module file application, and a timer expiration since the last save sequence. The method to determine if the data object has changed and what action to take when it has changed is described in greater detail with reference to  FIG. 14 . 
         [0117]      FIG. 14  is a flowchart illustrating an example of storing data. The method begins with step  174  where a processing module determines if a data object has changed based one or more of a query for change, a message from the processing module file application, a change determination policy, a degree of change detection, a comparison of the file to a copy of the file in the data object cache, and a timer expiration since the last save sequence. For example, the processing module determines that the data object has not changed when a comparison of the file to the file previously stored in the data object cache (e.g., as a result of the last save sequence) reveals that less than a threshold of characters are different. 
         [0118]    In another example, the processing module determines that the data object has changed when a comparison of the file to the file previously stored in the data object cache (e.g., as a result of the last save sequence) reveals that more than a threshold of characters are different and the timer from the last save sequence has expired. In another example, the processing module determines that the data object has changed when the processing module receives a message that the file has been closed (e.g., ending the file manipulation). The method repeats back to step  174  when the processing module determines that the data object has not changed. The method continues to step  176  when the processing module determines that the data object has changed. 
         [0119]    The method continues at step  176  where the processing module determines operational parameters including pillar width n, read threshold k, and an action policy (e.g., what to do when change is determined). Such a determination may be based on one or more of a vault lookup, a command, a predetermination, and a message. The method continues at step  178  where the processing module determines an action where the action may include storing a new copy of the file in the data object cache (e.g., in the file format and/or as encoded data slices) and/or storing a new copy, revision, or portion of the file in a dispersed storage network (DSN) memory as encoded data slices. Such a determination may be based on one or more of the action policy, the operational parameters, a data size indicator, a system activity level indicator, a vault lookup, a command, a message from the processing module, a predetermination, and a message. For example, the processing module determines the action to be store in the data object cache when the action policy indicates to store the file in the cache when the data size is below a threshold. 
         [0120]    In another example, the processing module determines the action to be store in the DSN memory when the action policy indicates to store the file in the DSN memory when the system level activity level indicator is below a threshold. The method branches to step  182  when the processing module determines the action to be store in the DSN memory. The method continues to step  180  when the processing module determines the action to be store in the data object cache. The method continues at step  180  where the processing module saves the file in the data object cache in the file format. For instance, the processing module saves the entire file. In another instance, the processing module saves a portion of the file that has changed since the last save sequence. Note that the processing module may create encoded data slices from the file in accordance with the operational parameters and store the slices in the data object cache. The method continues at step  22  where the processing module encodes a portion of the file in accordance with an error coding dispersal storage function to produce encoded data slices. The processing module sends the encoded data slices to the DSN memory with an updated revision number and a store command for storage in the DSN memory. 
         [0121]      FIG. 15  is a flowchart illustrating an example of retrieving data. The method begins with step  184  where a processing module receives a data object retrieval request message from a requester (e.g., an application that does not require the entire data object all at once including examples such as a media player, a text editor, etc.). Such a request may include one or more of a user ID, a data object name, a current position pointer (e.g., pointer within the data object), data object size, data type, a priority indicator, a security indicator, a performance indicator, a command, and a message. 
         [0122]    The method continues at step  186  where the processing module determines operational parameters which may include one or more of pillar width n, read threshold k, and a cache list (e.g., which data object may be where in the data object cache). Such a determination may be based on one or more of a vault lookup, a command, a predetermination, a data object name, data object size, data type, a priority indicator, a security indicator, a performance indicator, a command, and a message. 
         [0123]    The method continues at step  188  where the processing module determines a location of the data object which may include a data object cache and/or a dispersed storage network (DSN) memory. Such a determination may be based on one or more of the operational parameters, a cache list, a vault lookup, a command, a predetermination, a data object name, data object size, data type, a priority indicator, a security indicator, a performance indicator, a command, and a message. The method branches to step  196  when the processing module determines the location of the data object to be not in the cache. The method continues to step  190  when the processing module determines the location of the data object to be in the cache. 
         [0124]    The method continues at step  190  where the processing module retrieves the data object from the cache memory in accordance with a cache list. In an example, the data object is stored as encoded data slices. The processing module de-slices and decodes the encoded data slices in accordance with an error coding dispersal storage function to produce the data object in accordance with the operational parameters when the data object is stored as encoded data slices. The method continues at step  192  where the processing module sends the data object to the requester. The method branches to step  194 . 
         [0125]    The method continues at step  196  where the processing module retrieves encoded data slices from the DSN memory in accordance with the operational parameters and/or location determination when the processing module determines the location of the data object to be not in the cache. The method continues at step  198  where the processing module de-slices and decodes the slices utilizing the error coding dispersal storage function and in accordance with the operational parameters to produce the data object. The method continues at step  200  where the processing module stores the data object in data object cache memory and modifies the cache list to indicate that the data object is stored in the cache. Note that this may provide an improvement to the system such that the subsequent retrievals may be from the cache (e.g., faster). The method continues at step  202  where the processing module sends the data object to the requester. The method branches to step  194 . 
         [0126]    The method continues at step  194  where the processing module determines a read ahead which may include an amount of the data object to retrieve next (e.g., which may be similar to the last retrieval if the consumption pace is steady or it may be none). Such a determination may be based on one or more of the amount of the data object retrieved for consumption so far, the current position pointer, a history of reading ahead, time since the last retrieval, the operational parameters, a cache list, a vault lookup, a command, a predetermination, a data object name, data object size, data type, a priority indicator, a security indicator, a performance indicator, a command, a system activity level indicator, and a message. For example, the processing module determines the read ahead to be 10 megabytes when the history of reading ahead indicates that the last five read ahead retrievals where 10 mega bytes and the average time between retrievals was 5 minutes. The method repeats back to step  184 . 
         [0127]      FIG. 16  is another flowchart illustrating another example of storing data. The method begins with step  204  where a processing module (e.g., of a dispersed storage (DS) processing unit) receives a store data object message. The store data object message may include one or more of a command, a request, a user identity (ID), a data object name, a revision number, a data type, a data size, a priority indicator, a security indicator, a performance indicator, and metadata. The method continues at step  206  where the processing module determines operational parameters. Such operational parameters may include one or more of pillar width n, read threshold k, a write threshold (e.g., minimum number of pillars to confirm a successful write to confirm the store sequence), a transaction number, and identifiers of DS unit to utilize for storage. Such a determination may be based on one or more of a vault lookup, a virtual DSN address to physical location table lookup, a transaction number list, a last transaction number, a predetermination, a revision number, a query of DSN, a command, a user ID, a data object name, a data type, a data size, a priority indicator, a security indicator, a performance indicator, and other metadata. For example, the processing module determines that a first transaction number is 731 based on the last transaction number utilized was 730. 
         [0128]    The method continues at step  208  where the processing module dispersed storage error encodes the data in accordance with the operational parameters to produce a set of encoded data slices. The method continues at step  210  where the processing module generates a first transaction identifier regarding storage of the set of encoded data slices. Note that the first transaction identifier may include a transaction number and/or a request number. Such a generation of the first transaction identifier may include at least one of utilizing a coordinated universal time, utilizing a random number generator output, performing a function (e.g., increment, decrement, multiply times 2, etc.) based on at least one of a previous first transaction identifier and a previous second transaction identifier, performing a second function on the first transaction identifier to generate the second transaction identifier. 
         [0129]    The processing module outputs a plurality of write request messages to a plurality of dispersed storage (DS) units, wherein each of the plurality of write request messages includes the first transaction identifier and a corresponding one of the set of encoded data slices. One or more of the DS units may send a write response message (e.g., an acknowledgement) to the processing module in response to receiving the write request message. The processing module receives write response messages from the DS units. Note that the processing module may not receive an acknowledgement due to many potential errors and failures (e.g., DS unit failure, network failure, etc.). 
         [0130]    The method continues at step  212  where the processing module receives write response messages from at least some of the DS units, wherein each of the write response messages includes a reference to the first transaction identifier. Note that a write response message of the write response messages comprises at least one of an operation succeeded status code, a transaction conflict status code (e.g., slice is locked by another transaction), an addressing error status code (e.g., slice is not assigned to a responding DS unit), a check condition status code (e.g., an expected revision does not match what is currently stored), and an unauthorized status code (e.g., a requester is not authorized to write the slice). 
         [0131]    The processing module determines whether a write threshold number of favorable (e.g., with the operation succeeded status code) write response messages have been received within a time period. The method branches to step  216  when the processing module determines that the write threshold number of favorable write response messages have been received within the time period. The method continues to step  214  when the processing module determines that the write threshold number of favorable write response messages have not been received within the time period. Alternatively, the processing module determines that the write threshold number of favorable write response messages have not been received within the time period when the processing module receives at least one of the write response messages having an unfavorable response and, when a number of write response messages having the unfavorable response exceeds a second threshold. The method continues at step  214  where the processing module outputs a plurality of rollback transaction request messages to the plurality of DS units, wherein each of the plurality of rollback transaction request messages includes the first transaction identifier. Note that the DS unit deletes the encoded data slice, slice names, and first transaction identifier in response to receiving the rollback transaction request message. Next, the method branches back to step  208  where the processing module re-attempts to store the set of encoded data slices. 
         [0132]    The method continues at step  216  where the processing module reads directory information associated with the data. Such directory information may link a data identifier and revision identifier to a virtual DSN address of the location where the encoded data slices are stored in the DS units of the dispersed storage network memory. In an example, the processing module retrieves encoded directory slices from the plurality of DS units and decodes the encoded directory slices utilizing an error coding dispersal stored function to produce the directory information. The processing module updates directory information regarding storage of the data to produce updated directory information. For example, the processing module modifies the revision identifier to indicate a newer revision has been stored for the corresponding data identifier. 
         [0133]    The method continues at step  218  where the processing module determines if the directory information is as expected by one of more of comparing a transaction number of the last directory addition to an expected next transaction number (e.g., from the transaction number list) and by comparing the last entered data object name to the current data object name. Note that it is possible that another processing module is concurrently writing slices of a data object where the data object is targeted for the same directory position (e.g., a write collision). The method branches to step  222  when the processing module determines that the directory information is as expected. The method continues to step  220  when the processing module determines that the directory information is not as expected. The method continues at step  220  where the processing module sends an error message (e.g., to a dispersed storage managing unit), and may send a rollback request message to the plurality of DS units, and may branch back to step  208  to re-create and re-store encoded data slices to avoid a potential write conflict. 
         [0134]    The method continues at step  222  where the processing module dispersed storage error encodes the updated directory information to produce a set of encoded directory slices next. Next, the processing module generates a second transaction identifier regarding storage of the set of encoded directory slices wherein generating the second transaction identifier includes at least one of utilizing a coordinated universal time, utilizing a random number generator output, performing a function based on at least one of a previous transaction identifier, a previous second transaction identifier, performing a second function on the first transaction identifier to generate the second transaction identifier. The processing module outputs a second plurality of write request messages to a second plurality of DS units, wherein each of the second plurality of write request messages includes the second transaction identifier and a corresponding one of the set of encoded directory slices. Alternatively, the processing module outputs the second plurality of write request messages to the plurality of DS units. 
         [0135]    Alternatively, the processing module outputs a plurality of read request messages that includes a plurality of slice names corresponding to the updated directory information. Next, the processing module receives a plurality of read response messages that include a slice revision. Next, the processing module establishes the expected slice revision as the slice revision. Next, the processing module outputs the second plurality of write request messages to the plurality of DS units, wherein each of the second plurality of write request messages further includes the expected slice revision. The DS units may send an acknowledgement to the DS processing in response to receiving the data object name and second transaction number. 
         [0136]    The processing module receives second write response messages (e.g., acknowledgements) from at least some of the plurality of DS units. Alternatively, the processing module interprets the second write response messages for confirmation of the expected slice revision. Note that the second write response message of the second write response messages comprises at least one of an operation succeeded status code, a transaction conflict status code, an addressing error status code, a check condition status code (e.g., the expected slice revision does not equal a current slice revision), and an unauthorized status code. Note that the processing module may not receive a second write response message due to many potential errors and failures (e.g., DS unit failure, network failure). 
         [0137]    The method continues at step  224  where the processing module determines whether at least a second write threshold number of favorable (e.g., operation succeeded without error) second write response messages have been received from the DS units within a time period. The method branches back to step  216  where the processing module re-updates (e.g., re-reads and updates) the directory information regarding storage of the data, re-disperse error encodes the directory information to re-produce the set of encoded directory slices, and outputs at least some of the second plurality of write request messages regarding the reproduced set of encoded directory slices at step  222  to try again when the processing module determines that at least the second write threshold number of favorable second write response messages have not been received within a time period. The method continues to step  226  when the processing module determines that at least the second write threshold number of favorable second write response messages have been received. 
         [0138]    The method continues at step  226  where the processing module outputs a plurality of data commit request messages regarding the set of encoded data slices to the plurality of DS units, wherein each of the plurality of data commit request messages includes the first transaction identifier. Next, the processing module outputs the plurality of directory commit request messages regarding the set of encoded directory slices to the second plurality of DS units, wherein each of the plurality of directory commit request messages includes the second transaction identifier. Alternatively, the processing module outputs a plurality of commit request messages regarding the set of encoded data slices and the set of encoded directory slices to the plurality of DS units, wherein each of the plurality of commit request messages includes the first and second transaction identifiers. Alternatively, the processing module outputs the plurality of commit request messages regarding the set of encoded data slices and the set of encoded directory slices to the plurality of DS units. The method of operation of the DS unit is discussed in greater detail with reference to  FIG. 17 . 
         [0139]      FIG. 17  is a flowchart illustrating an example of storing an encoded data slice. The method begins with step  228  where a processing module (e.g., of a dispersed storage (DS) unit) receives a write request message from a dispersed storage (DS) processing module, wherein the write request message includes a slice name (e.g., of the slice to store), a DS processing module most-recent slice revision, a new slice revision (e.g., of the slice to store), and an encoded directory slice of directory information regarding storage of data. Note that DS processing module most-recent slice revision may be a revision number that the processing module of the DS unit previously sent to the DS processing module in response to a previous encoded directory slice query. 
         [0140]    The method continues at step  230  where the processing module obtains a DS unit most-recent slice revision from local memory based on the slice name. The method continues at step  232  where the processing module determines whether the DS unit most-recent slice revision compares favorably to the DS processing module most-recent slice revision from the request. The processing module determines that the DS unit most-recent slice revision compares favorably to the DS processing module most-recent slice revision when the DS unit most-recent slice revision is substantially the same as the DS processing module most-recent slice revision. In addition, the processing module may check for other possible error conditions. In an example, the processing module verifies that the slice name is within a range that is assigned to the processing module (e.g., the DS unit). The processing module sends a write response message that includes an addressing error status code when the processing module determines that the slice name is not within the range. In another example, the processing module verifies that a requester that initiated the write request is authenticated and has an appropriate permissions level. The processing module sends a write response message that includes an unauthorized status code when the processing module determines that requester is not authenticated or does not have the appropriate permissions level. 
         [0141]    The method branches to step  236  when the processing module determines that the DS unit most-recent slice revision compares favorably to the DS processing module most-recent slice revision. The method continues to step  234  when the processing module determines that the DS unit most-recent slice revision compares unfavorably to the DS processing module most-recent slice revision. The method continues at step  234  where the processing module generates a write response message to include a condition status code (e.g., a check condition status code) indicating the unfavorable comparison. Next, the processing module sends the write response message to the DS processing module. 
         [0142]    The method continues at step  236  where the processing module stores the encoded directory slice. In addition, the processing module may generate a write response message that includes an operation succeeded status code. Next, the processing module sends the write response message to the DS processing module. The method continues at step  238  where the processing module stores the new slice revision as the DS unit most-recent slice revision when the transaction identifier is null. The processing module stores the new slice revision as the DS unit most recent slice revision when the transaction identifier is not null and a commit transaction message is subsequently received as discussed below. 
         [0143]    Alternatively, or in addition to, the processing module receives the write request message, wherein the write request message further includes a DS processing module transaction identifier. Next, the processing module determines whether the slice name has a locked state based on a local state indicator. The processing module generates a write response message that includes a transaction conflict status code and sends the write response message to the DS processing module when the slice name has the locked state and a DS unit transaction indicator associated with the encoded directory slice compares unfavorably to the DS processing module transaction identifier. The processing module updates the local state indicator to indicate that the slice name has the locked state and stores the DS processing module transaction identifier as the DS unit transaction identifier when the slice name does not have a locked state. 
         [0144]    In addition, the processing module may receive a commit transaction request message regarding storage of at least one of an encoded data slice and an encoded directory slice, wherein the commit transaction request message includes at least one transaction identifier. Next, the processing module identifies one or more slice names based on the at least one transaction identifier and for each of the one or more slices names, updates a slice status indicator to indicate the at least one of the encoded data slice and the encoded directory slice is visible. In addition, the processing module may update a current revision indicator associated with the slice name and transaction identifier to indicate a revision associated with the slice name. In addition, the processing module may update the slice status indicator to indicate that the slice name has an unlocked state subsequent to indicating that the at least one of the encoded data slice and the encoded directory slice is visible. 
         [0145]    Alternatively, the processing module receives a commit transaction request message regarding storage of at least one of an encoded data slice and an encoded directory slice, wherein the commit transaction request message includes first and second transaction identifiers of the at least one transaction identifier, wherein the first transaction identifier is associated with the encoded data slice and the second transaction identifier is associated with the encoded directory slice. Next, the processing module updates a first slice status indicator to indicate that the encoded data slice is visible, and re-updates the first slice status indicator to indicate that the encoded data slice is not visible when a DS unit memory error exists. The processing module updates a second slice status indicator to indicate that the encoded directory slice is visible and re-updates the second slice status indicator to indicate that the encoded directory slice is not visible when the DS unit memory error exists. 
         [0146]    As may be used herein, the terms “substantially” and “approximately” provides an industry-accepted tolerance for its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from less than one percent to fifty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. Such relativity between items ranges from a difference of a few percent to magnitude differences. As may also be used herein, the term(s) “operably coupled to”, “coupled to”, and/or “coupling” 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) where, for indirect coupling, the intervening item does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. 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” or “operably coupled to” indicates that an item includes one or more of power connections, input(s), output(s), etc., to perform, when activated, 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. As may be used herein, the term “compares favorably”, indicates that a comparison between two or more items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal  1  has a greater magnitude than signal  2 , a favorable comparison may be achieved when the magnitude of signal  1  is greater than that of signal  2  or when the magnitude of signal  2  is less than that of signal  1 . 
         [0147]    While the transistors in the above described figure(s) is/are shown as field effect transistors (FETs), as one of ordinary skill in the art will appreciate, the transistors may be implemented using any type of transistor structure including, but not limited to, bipolar, metal oxide semiconductor field effect transistors (MOSFET), N-well transistors, P-well transistors, enhancement mode, depletion mode, and zero voltage threshold (VT) transistors. 
         [0148]    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. 
         [0149]    The present invention has been described, at least in part, in terms of one or more embodiments. An embodiment of the present invention is used herein to illustrate the present invention, an aspect thereof, a feature thereof, a concept thereof, and/or an example thereof. A physical embodiment of an apparatus, an article of manufacture, a machine, and/or of a process that embodies the present invention may include one or more of the aspects, features, concepts, examples, etc., described with reference to one or more of the embodiments discussed herein. 
         [0150]    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.