USING LOCKS TO PREVENT MULTIPLE REBUILDS OF THE SAME SOURCE

Abstract

A method includes determining to rebuild one or more encoded data slices (EDSs) of a plurality of sets of EDSs. When determined to rebuild the one or more EDSs, the method includes sending a lock request to a set of storage units (SUs) regarding the plurality of sets of EDSs. The method further includes determining whether at least a decode threshold number of favorable lock responses is received from the set of SUs. When the at least the decode threshold number is received, the method further includes recovering one or more sets of EDSs to rebuild the one or more EDSs to produce one or more rebuilt EDSs. For a rebuilt EDS, the method further includes determining whether a SU that is targeted to receive the rebuilt EDS is available to store the rebuilt EDS, and when the SU is available, sending the rebuilt EDS to the SU.

Claims

1. A method comprises: determining, by a first rebuilding agent of a plurality of rebuilding agents of a dispersed storage network (DSN), to rebuild one or more encoded data slices of a plurality of sets of encoded data slices; when determined to rebuild the one or more encoded data slices, sending, by the first rebuilding agent, a lock request to a set of storage units of the DSN regarding the plurality of sets of encoded data slices; determining, by the first rebuilding agent, whether at least a decode threshold number of favorable lock responses is received from the set of storage units; when the at least the decode threshold number of favorable lock responses is received, recovering, by the first rebuilding agent, one or more sets of encoded data slices of the plurality of sets of encoded data slices to rebuild the one or more encoded data slices to produce one or more rebuilt encoded data slices; for a rebuilt encoded data slice of the one or more rebuilt encoded data slices, determining, by the first rebuilding agent, whether a storage unit of the set of storage units that is targeted to receive the rebuilt encoded data slice is available to store the rebuilt encoded data slice; and when the storage unit is available to store the rebuilt encoded data slice, sending, by the first rebuilding agent, the rebuilt encoded data slice to the storage unit.

2. The method of claim 1, wherein the plurality of sets of encoded data slices comprises one of: a plurality of sets of encoded data slices of a data object; and a plurality of sets of encoded data slices of multiple data objects.

3. The method of claim 1 further comprises: when the at least the decode threshold number of favorable lock responses is not received, sending, by the first rebuilding agent, a withdraw lock request message to the set of storage units; and determining, by the first rebuilding agent, to rebuild one or more encoded data slices of another plurality of sets of encoded data slices.

4. The method of claim 3 further comprises: when the first rebuilding agent has rebuilt the one or more encoded data slices of the another plurality of sets of encoded data slices, sending, by the first rebuilding agent, another lock request to the set of storage units regarding the plurality of sets of encoded data slices.

5. The method of claim 1 further comprises: when the storage unit is not available to store the rebuilt encoded data slice, determining by the first rebuilding agent, whether another storage unit of the DSN is available to store the rebuilt encoded data slice; and when the another storage unit is available, sending, by the first rebuilding agent, the rebuilt encoded data slice to the another storage unit.

6. The method of claim 1 further comprises: when the at least the decode threshold number of favorable lock responses is received, determining, by the first rebuilding agent, whether another rebuilding agent of the plurality of rebuilding agents has identified a different encoded data slice of the one or more sets of encoded data slices rebuilding; and when the another rebuilding agent has identified a different encoded data slice for rebuilding: rebuilding, by the first rebuilding agent, the different encoded data slice from the one or more sets of encoded data slices to produce a different rebuilt encoded data slice; and informing, by the first rebuilding agent, the another rebuilding agent that the different encoded data slice has been rebuilt.

7. The method of claim 6, wherein the rebuilding the different encoded data slice comprises: sending, by the first rebuilding agent, a message to the another rebuilding agent, wherein the message indicates the first rebuilding agent has the at least the decode threshold number of favorable lock responses and includes a request to rebuild the different encoded data slice; and when a favorable response to the message is received, rebuilding, by the first rebuilding agent, the different encoded data slice.

8. A computing device of a plurality of computing devices of a dispersed storage network (DSN), the computing device comprises: an interface; memory; and a processing module operably coupled to the memory and the interface, wherein the processing module is operable to: determine to rebuild one or more encoded data slices of a plurality of sets of encoded data slices; when determined to rebuild the one or more encoded data slices, send a lock request to a set of storage units of the DSN regarding the plurality of sets of encoded data slices; determine whether at least a decode threshold number of favorable lock responses is received from the set of storage units; when the at least the decode threshold number of favorable lock responses is received, recover one or more sets of encoded data slices of the plurality of sets of encoded data slices to rebuild the one or more encoded data slices to produce one or more rebuilt encoded data slices; for a rebuilt encoded data slice of the one or more rebuilt encoded data slices, determine whether a storage unit of the set of storage units that is targeted to receive the rebuilt encoded data slice is available to store the rebuilt encoded data slice; and when the storage unit is available to store the rebuilt encoded data slice, send the rebuilt encoded data slice to the storage unit.

9. The computing device of claim 8, wherein the plurality of sets of encoded data slices comprises one of: a plurality of sets of encoded data slices of a data object; and a plurality of sets of encoded data slices of multiple data objects.

10. The computing device of claim 8, wherein the processing module further functions to: when the at least the decode threshold number of favorable lock responses is not received, send a withdraw lock request message to the set of storage units; and determine to rebuild one or more encoded data slices of another plurality of sets of encoded data slices.

11. The computing device of claim 10, wherein the processing module further functions to: when the processing module has rebuilt the one or more encoded data slices of the another plurality of sets of encoded data slices, send another lock request to the set of storage units regarding the plurality of sets of encoded data slices.

12. The computing device of claim 8, wherein the processing module further functions to: when the storage unit is not available to store the rebuilt encoded data slice, determine whether another storage unit of the DSN is available to store the rebuilt encoded data slice; and when the another storage unit is available, send the rebuilt encoded data slice to the another storage unit.

13. The computing device of claim 8, wherein the processing module further functions to: when the at least the decode threshold number of favorable lock responses is received, determine whether another processing module of another computing device of the plurality of computing devices of the DSN has identified a different encoded data slice of the one or more sets of encoded data slices rebuilding; and when the another processing module has identified a different encoded data slice for rebuilding: rebuild the different encoded data slice from the one or more sets of encoded data slices to produce a different rebuilt encoded data slice; and inform the another processing module that the different encoded data slice has been rebuilt.

14. The computing device of claim 13, wherein the processing module further functions to: send a message to the another processing module, wherein the message indicates the processing module has the at least the decode threshold number of favorable lock responses and includes a request to rebuild the different encoded data slice; and when a favorable response to the message is received, rebuild the different encoded data slice.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0008] FIG. 1 is a schematic block diagram of an embodiment of a dispersed or distributed storage network (DSN) in accordance with the present invention;

[0009] FIG. 2 is a schematic block diagram of an embodiment of a computing core in accordance with the present invention;

[0010] FIG. 3 is a schematic block diagram of an example of dispersed storage error encoding of data in accordance with the present invention;

[0011] FIG. 4 is a schematic block diagram of a generic example of an error encoding function in accordance with the present invention;

[0012] FIG. 5 is a schematic block diagram of a specific example of an error encoding function in accordance with the present invention;

[0013] FIG. 6 is a schematic block diagram of an example of a slice name of an encoded data slice (EDS) in accordance with the present invention;

[0014] FIG. 7 is a schematic block diagram of an example of dispersed storage error decoding of data in accordance with the present invention;

[0015] FIG. 8 is a schematic block diagram of a generic example of an error decoding function in accordance with the present invention;

[0016] FIG. 9 is a schematic block diagram of an embodiment of rebuilding one or more encoded data slices of a plurality of sets of encoded data slices by a rebuilding agent of a plurality of rebuilding agents of a dispersed storage network (DSN) in accordance with the present invention; and

[0017] FIG. 10 is a logic diagram of an example of a method of rebuilding one or more encoded data slices of a plurality of sets of encoded data slices by a rebuilding agent of a plurality of rebuilding agents of a dispersed storage network (DSN) in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] FIG. 1 is a schematic block diagram of an embodiment of a dispersed, or distributed, storage network (DSN) 10 that includes a plurality of computing devices 12-16, a managing unit 18, an integrity processing unit 20, and a DSN memory 22. The components of the DSN 10 are coupled to a network 24, which may include one or more wireless and/or wire lined communication systems; one or more non-public intranet systems and/or public internet systems; and/or one or more local area networks (LAN) and/or wide area networks (WAN).

[0019] The DSN memory 22 includes a plurality of storage units 36 that may be located at geographically different sites (e.g., one in Chicago, one in Milwaukee, etc.), at a common site, or a combination thereof. For example, if the DSN memory 22 includes eight storage units 36, each storage unit is located at a different site. As another example, if the DSN memory 22 includes eight storage units 36, all eight storage units are located at the same site. As yet another example, if the DSN memory 22 includes eight storage units 36, a first pair of storage units are at a first common site, a second pair of storage units are at a second common site, a third pair of storage units are at a third common site, and a fourth pair of storage units are at a fourth common site. Note that a DSN memory 22 may include more or less than eight storage units 36. Further note that each storage unit 36 includes a computing core (as shown in FIG. 2, or components thereof) and a plurality of memory devices for storing dispersed error encoded data.

[0020] Each of the computing devices 12-16, the managing unit 18, and the integrity processing unit 20 include a computing core 26, which includes network interfaces 30-33. Computing devices 12-16 may each be a portable computing device and/or a fixed computing device. A portable computing device may be a social networking device, a gaming device, a cell phone, a smart phone, a digital assistant, a digital music player, a digital video player, a laptop computer, a handheld computer, a tablet, a video game controller, and/or any other portable device that includes a computing core. A fixed computing device may be a computer (PC), 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. Note that each of the managing unit 18 and the integrity processing unit 20 may be separate computing devices, may be a common computing device, and/or may be integrated into one or more of the computing devices 12-16 and/or into one or more of the storage units 36.

[0021] Each interface 30, 32, and 33 includes software and hardware to support one or more communication links via the network 24 indirectly and/or directly. For example, interface 30 supports a communication link (e.g., wired, wireless, direct, via a LAN, via the network 24, etc.) between computing devices 14 and 16. As another example, interface 32 supports communication links (e.g., a wired connection, a wireless connection, a LAN connection, and/or any other type of connection to/from the network 24) between computing devices 12 & 16 and the DSN memory 22. As yet another example, interface 33 supports a communication link for each of the managing unit 18 and the integrity processing unit 20 to the network 24.

[0022] Computing devices 12 and 16 include a dispersed storage (DS) client module 34, which enables the computing device to dispersed storage error encode and decode data as subsequently described with reference to one or more of FIGS. 3-8. In this example embodiment, computing device 16 functions as a dispersed storage processing agent for computing device 14. In this role, computing device 16 dispersed storage error encodes and decodes data on behalf of computing device 14. With the use of dispersed storage error encoding and decoding, the DSN 10 is tolerant of a significant number of storage unit failures (the number of failures is based on parameters of the dispersed storage error encoding function) without loss of data and without the need for a redundant or backup copies of the data. Further, the DSN 10 stores data for an indefinite period of time without data loss and in a secure manner (e.g., the system is very resistant to unauthorized attempts at accessing the data).

[0023] In operation, the managing unit 18 performs DS management services. For example, the managing unit 18 establishes distributed data storage parameters (e.g., vault creation, distributed storage parameters, security parameters, billing information, user profile information, etc.) for computing devices 12-14 individually or as part of a group of user devices. As a specific example, the managing unit 18 coordinates creation of a vault (e.g., a virtual memory block associated with a portion of an overall namespace of the DSN) within the DSTN memory 22 for a user device, a group of devices, or for public access and establishes per vault dispersed storage (DS) error encoding parameters for a vault. The managing unit 18 facilitates storage of DS error encoding parameters for each vault by updating registry information of the DSN 10, where the registry information may be stored in the DSN memory 22, a computing device 12-16, the managing unit 18, and/or the integrity processing unit 20.

[0024] The DSN managing unit 18 creates and stores user profile information (e.g., an access control list (ACL)) in local memory and/or within memory of the DSN memory 22. The user profile information includes authentication information, permissions, and/or the security parameters. The security parameters may include encryption/decryption scheme, one or more encryption keys, key generation scheme, and/or data encoding/decoding scheme.

[0025] The DSN managing unit 18 creates billing information for a particular user, a user group, a vault access, public vault access, etc. For instance, the DSTN managing unit 18 tracks the number of times a user accesses a non-public vault and/or public vaults, which can be used to generate a per-access billing information. In another instance, the DSTN 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 billing information.

[0026] As another example, the managing unit 18 performs network operations, network administration, and/or network maintenance. Network operations includes authenticating user data allocation requests (e.g., read and/or write requests), managing creation of vaults, establishing authentication credentials for user devices, adding/deleting components (e.g., user devices, storage units, and/or computing devices with a DS client module 34) to/from the DSN 10, and/or establishing authentication credentials for the storage units 36. Network administration includes monitoring devices and/or units for failures, maintaining vault information, determining device and/or unit activation status, determining device and/or unit loading, and/or determining any other system level operation that affects the performance level of the DSN 10. Network maintenance includes facilitating replacing, upgrading, repairing, and/or expanding a device and/or unit of the DSN 10.

[0027] The integrity processing unit 20 performs rebuilding of ‘bad’ or missing encoded data slices. At a high level, the integrity processing unit 20 performs rebuilding by periodically attempting to retrieve/list encoded data slices, and/or slice names of the encoded data slices, from the DSN memory 22. For retrieved encoded slices, they are checked for errors due to data corruption, outdated version, etc. If a slice includes an error, it is flagged as a ‘bad’ slice. For encoded data slices that were not received and/or not listed, they are flagged as missing slices. Bad and/or missing slices are subsequently rebuilt using other retrieved encoded data slices that are deemed to be good slices to produce rebuilt slices. The rebuilt slices are stored in the DSTN memory 22.

[0028] 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 module 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 one or more 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.

[0029] The DSN interface module 76 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.). The DSN interface module 76 and/or the network interface module 70 may function as one or more of the interface 30-33 of FIG. 1. Note that the IO device interface module 62 and/or the memory interface modules 66-76 may be collectively or individually referred to as IO ports.

[0030] FIG. 3 is a schematic block diagram of an example of dispersed storage error encoding of data. When a computing device 12 or 16 has data to store it disperse storage error encodes the data in accordance with a dispersed storage error encoding process based on dispersed storage error encoding parameters. The dispersed storage error encoding parameters include an encoding function (e.g., information dispersal algorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding, non-systematic encoding, on-line codes, etc.), a data segmenting protocol (e.g., data segment size, fixed, variable, etc.), and per data segment encoding values. The per data segment encoding values include a total, or pillar width, number (T) of encoded data slices per encoding of a data segment i.e., in a set of encoded data slices); a decode threshold number (D) of encoded data slices of a set of encoded data slices that are needed to recover the data segment; a read threshold number (R) of encoded data slices to indicate a number of encoded data slices per set to be read from storage for decoding of the data segment; and/or a write threshold number (W) to indicate a number of encoded data slices per set that must be accurately stored before the encoded data segment is deemed to have been properly stored. The dispersed storage error encoding parameters may further include slicing information (e.g., the number of encoded data slices that will be created for each data segment) and/or slice security information (e.g., per encoded data slice encryption, compression, integrity checksum, etc.).

[0031] In the present example, Cauchy Reed-Solomon has been selected as the encoding function (a generic example is shown in FIG. 4 and a specific example is shown in FIG. 5); the data segmenting protocol is to divide the data object into fixed sized data segments; and the per data segment encoding values include: a pillar width of 5, a decode threshold of 3, a read threshold of 4, and a write threshold of 4. In accordance with the data segmenting protocol, the computing device 12 or 16 divides the data (e.g., a file (e.g., text, video, audio, etc.), a data object, or other data arrangement) into a plurality of fixed sized data segments (e.g., 1 through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more). The number of data segments created is dependent of the size of the data and the data segmenting protocol.

[0032] The computing device 12 or 16 then disperse storage error encodes a data segment using the selected encoding function (e.g., Cauchy Reed-Solomon) to produce a set of encoded data slices. FIG. 4 illustrates a generic Cauchy Reed-Solomon encoding function, which includes an encoding matrix (EM), a data matrix (DM), and a coded matrix (CM). The size of the encoding matrix (EM) is dependent on the pillar width number (T) and the decode threshold number (D) of selected per data segment encoding values. To produce the data matrix (DM), the data segment is divided into a plurality of data blocks and the data blocks are arranged into D number of rows with Z data blocks per row. Note that Z is a function of the number of data blocks created from the data segment and the decode threshold number (D). The coded matrix is produced by matrix multiplying the data matrix by the encoding matrix.

[0033] FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encoding with a pillar number (T) of five and decode threshold number of three. In this example, a first data segment is divided into twelve data blocks (D1-D12). The coded matrix includes five rows of coded data blocks, where the first row of X11-X14 corresponds to a first encoded data slice (EDS 1_1), the second row of X21-X24 corresponds to a second encoded data slice (EDS 2_1), the third row of X31-X34 corresponds to a third encoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to a fourth encoded data slice (EDS 4_1), and the fifth row of X51-X54 corresponds to a fifth encoded data slice (EDS 5_1). Note that the second number of the EDS designation corresponds to the data segment number.

[0034] Returning to the discussion of FIG. 3, the computing device also creates a slice name (SN) for each encoded data slice (EDS) in the set of encoded data slices. A typical format for a slice name 60 is shown in FIG. 6. As shown, the slice name (SN) 60 includes a pillar number of the encoded data slice (e.g., one of 1-T), a data segment number (e.g., one of 1-Y), a vault identifier (ID), a data object identifier (ID), and may further include revision level information of the encoded data slices. The slice name functions as, at least part of, a DSN address for the encoded data slice for storage and retrieval from the DSN memory 22.

[0035] As a result of encoding, the computing device 12 or 16 produces a plurality of sets of encoded data slices, which are provided with their respective slice names to the storage units for storage. As shown, the first set of encoded data slices includes EDS 1_1 through EDS 5_1 and the first set of slice names includes SN 1_1 through SN 5_1 and the last set of encoded data slices includes EDS 1_Y through EDS 5_Y and the last set of slice names includes SN 1_Y through SN 5_Y.

[0036] FIG. 7 is a schematic block diagram of an example of dispersed storage error decoding of a data object that was dispersed storage error encoded and stored in the example of FIG. 4. In this example, the computing device 12 or 16 retrieves from the storage units at least the decode threshold number of encoded data slices per data segment. As a specific example, the computing device retrieves a read threshold number of encoded data slices.

[0037] To recover a data segment from a decode threshold number of encoded data slices, the computing device uses a decoding function as shown in FIG. 8. As shown, the decoding function is essentially an inverse of the encoding function of FIG. 4. The coded matrix includes a decode threshold number of rows (e.g., three in this example) and the decoding matrix in an inversion of the encoding matrix that includes the corresponding rows of the coded matrix. For example, if the coded matrix includes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2, and 4, and then inverted to produce the decoding matrix.

[0038] FIG. 9 is a schematic block diagram of an example of rebuilding one or more encoded data slices of a plurality of sets of encoded data slices by a rebuilding agent of a plurality of rebuilding agents of a dispersed storage network (DSN). FIG. 9 includes rebuilding agents 1-3 (e.g., RA 1, RA 2, and RA 3), and a one or more encoded data slices of a plurality of sets of encoded data slices a plurality of sets of encoded data slices. A rebuilding agent of the plurality of rebuilding agents may be a separate computing device, separate processing module, and/or may be integrated into one or more of the computing devices 12-16 and/or into one or more of the storage units 36 of FIG. 1. The plurality of sets of encoded data slices may be a plurality of sets of encoded data slices of a data object or a plurality of sets of encoded data slices of multiple data objects.

[0039] In an example of operation, a first rebuilding agent of a plurality of rebuilding agents (RA 1) determines to rebuild encoded data slices EDS 4_1, EDS 3_3, and EDS 4_5. EDS 3_3 is an encoded data slice of a set of encoded data slices EDS 3_1 through EDS 3_Y. EDS 4_1 and EDS 4_5 are encoded data slices of a set of encoded data slices EDS 4_1 through EDS 4_Y. For example, RA 1 has detected or received an alert by another device within the DSN that EDS 4_1, EDS 4_5, and EDS 3_3 are stored in error (e.g., missing and/or corrupted) and require rebuilding. RA 1 will then send a lock request to a set of storage units of the DSN regarding the plurality of sets of encoded data slices to exclusively access the slices necessary for the rebuild. A successful lock ensures that two different rebuilding agents do not attempt to rebuild the same data at the same time, as this would be redundant and a waste of resources.

[0040] The rebuilding agent RA 1 will then determine whether at least a decode threshold number of favorable lock responses is received from the set of storage units. To execute a rebuild of an encoded data slice of a set of encoded data slices, the rebuilding agent needs at least a decode threshold number of encoded data slices from the set of encoded data slices. The rebuilding process includes retrieving a decode threshold number of encoded data slices from the set of encoded data slices, decoding the retrieved encoded data slices using the DS error encoding parameters to recapture a corresponding data segment, and re-encoding the data segment using the DS error encoding parameters to rebuild the corrupted encoded data slice. As such, if EDS 3_3 is from a set of encoded data slices of a data segment having a decode threshold of 3, 3 encoded data slices from that set are needed to perform a rebuild of EDS 3_3. Because each encoded data slice of the set of data slices are stored on a separate storage unit of a set of storage units, at least a decode threshold number of storage units from the set of storage units must return a favorable lock response to the rebuilding agent in order for the rebuilding agent to perform a locked rebuild.

[0041] When the at least the decode threshold number of favorable lock responses is received from the set of storage units, RA 1 will recover one or more sets of encoded data slices of the plurality of encoded data slices to rebuild the one or more encoded data slices to produce one or more rebuilt encoded data slices. For example, RA 1 will recover at least a decode number of slices from EDS set EDS 3_1 through EDS 3_Y in order to rebuild EDS 3_3. RA 1 will recover at least a decode number of slices from EDS set EDS 4_1 through EDS 4_Y in order to rebuild EDS 4_1 and EDS 4_5.

[0042] For each rebuilt encoded data slice, the rebuilding agent will determine whether a storage unit of the set of storage units that is targeted to receive the rebuilt encoded data slice is available to store the rebuilt encoded data slice. A storage unit may be considered available when the storage unit is online and not in a maintenance mode. When the storage unit is available to store the rebuilt encoded data slice, the rebuilding agent will send the rebuilt encoded data slice to the storage unit. When the storage unit is not available to store the rebuilt encoded data slice, RA 1 will determine whether another storage unit of the DSN is available to store the rebuilt encoded data slice. When the other storage unit is available, RA 1 will then send the rebuilt encoded data slice to the other storage unit.

[0043] When the at least the decode threshold number of favorable lock responses is received, RA 1 may also determine whether another rebuilding agent of the plurality of rebuilding agents has identified a different encoded data slice of the one or more sets of encoded data slices rebuilding. For example, RA 1 may determine that RA 3 has identified EDS 3_Y-1 for rebuilding and EDS 3_Y-1 is within the same set of encoded data slices as EDS 3_3. In this situation, RA 1 may also rebuild EDS 3_Y-1 to produce a rebuilt EDS 3_Y-1, and inform RA 3 that EDS 3_Y-1 has been rebuilt. Alternatively, RA 1 may send a message to RA 3 indicating RA 1 has the at least the decode threshold number of favorable lock responses and requesting to rebuild EDS 3_Y-1. When a favorable response to the message is received, RA 1 will then rebuild EDS 3_Y-1.

[0044] If the at least the decode threshold number of favorable lock responses is not received, (e.g., another rebuilding agent has a lock on the set of storage units) RA 1 will send a withdraw lock request message to the set of storage units, and determine to rebuild one or more encoded data slices of another plurality of sets of encoded data slices. After RA 1 has rebuilt the one or more encoded data slices of the another plurality of sets of encoded data slices, RA 1 may then try again to rebuild slices EDS 3_3, EDS 4_1, EDS 4_5 and send another lock request to the set of storage units regarding the corresponding plurality of sets of encoded data slices.

[0045] FIG. 10 is a logic diagram of an example of a method of rebuilding one or more encoded data slices of a plurality of sets of encoded data slices by a rebuilding agent of a plurality of rebuilding agents of a dispersed storage network (DSN). The method begins with step 82 where a first rebuilding agent of a plurality of rebuilding agents determines to rebuild one or more encoded data slices of a plurality of sets of encoded data slices. For example, the first rebuilding agent may have detected or received an alert by another device within the DSN that the one or more encoded data slices of a plurality of sets of encoded data slices are stored in error (e.g., missing and/or corrupted) and require rebuilding. The method continues with step 84 where the first rebuilding agent sends a lock request to a set of storage units of the DSN regarding the plurality of sets of encoded data slices to exclusively access the slices necessary for the rebuild. A successful lock ensures that two different rebuilding agents do not attempt to rebuild the same data at the same time, as this would be redundant and a waste of resources.

[0046] The method continues with step 86 where the first rebuilding agent determines whether at least a decode threshold number of favorable lock responses is received from the set of storage units. To execute a rebuild of an encoded data slice of a set of encoded data slices, the rebuilding agent needs at least a decode threshold number of encoded data slices from the set of encoded data slices. The rebuilding process includes retrieving a decode threshold number of encoded data slices from the set of encoded data slices, decoding the retrieved encoded data slices using the DS error encoding parameters to recapture a corresponding data segment, and re-encoding the data segment using the DS error encoding parameters to rebuild the corrupted encoded data slice. Because each encoded data slice of the set of data slices are stored on a separate storage unit of a set of storage units, at least a decode threshold number of storage units from the set of storage units must return a favorable lock response to the rebuilding agent in order for the rebuilding agent to perform a locked rebuild.

[0047] When the at least the decode threshold number of favorable lock responses is received from the set of storage units, the method continues with step 88 where the first rebuilding agent recovers one or more sets of encoded data slices of the plurality of sets encoded data slices to rebuild the one or more encoded data slices to produce one or more rebuilt encoded data slices. The method continues with step 90 where, for each rebuilt encoded data slice, the first rebuilding agent determines whether a storage unit of the set of storage units that is targeted to receive the rebuilt encoded data slice is available to store the rebuilt encoded data slice. A storage unit may be considered available when the storage unit is online and not in a maintenance mode. When the storage unit is available to store the rebuilt encoded data slice, the method continues with step 92 where the first rebuilding agent sends the rebuilt encoded data slice to the storage unit. When the storage unit is not available to store the rebuilt encoded data slice, the method continues with step 94 where the first rebuilding agent determines whether another storage unit of the DSN is available to store the rebuilt encoded data slice. When the other storage unit is available, the method continues with step 96 where the first rebuilding agent sends the rebuilt encoded data slice to the other storage unit. When the other storage unit is not available, the method branches back to step 90 where for each rebuilt encoded data slice, the first rebuilding agent determines whether a storage unit of the set of storage units that is targeted to receive the rebuilt encoded data slice is now available to store the rebuilt encoded data slice.

[0048] When the at least the decode threshold number of favorable lock responses is received at step 86, the first rebuilding agent may also determine whether another rebuilding agent of the plurality of rebuilding agents has identified a different encoded data slice of the one or more sets of encoded data slices rebuilding. When the other rebuilding agent has identified a different encoded data slice for rebuilding, the first rebuilding agent rebuilds the different encoded data slice from the one or more sets of encoded data slices to produce a different rebuilt encoded data slice, and informs the other rebuilding agent that the different encoded data slice has been rebuilt. Alternatively, the first rebuilding agent may send a message to other rebuilding agent where the message indicates the first rebuilding agent has the at least the decode threshold number of favorable lock responses and includes a request to rebuild the different encoded data slice. When a favorable response to the message is received, the first rebuilding agent rebuilds the different encoded data slice.

[0049] When, at step 86, the first rebuilding agent determines that the at least the decode threshold number of favorable lock responses is not received, (e.g., another rebuilding agent has a lock on the set of storage units) the method continues with step 98 where the first rebuilding agent sends a withdraw lock request message to the set of storage units. The method continues with step 100 where the first rebuilding agent determines to rebuild one or more encoded data slices of another plurality of sets of encoded data slices. When the first rebuilding agent has rebuilt the one or more encoded data slices of the another plurality of sets of encoded data slices, the first rebuilding agent may the first rebuilding agent may send another lock request to the set of storage units regarding the plurality of sets of encoded data slices.

[0050] It is noted that terminologies as may be used herein such as bit stream, stream, signal sequence, etc. (or their equivalents) have been used interchangeably to describe digital information whose content corresponds to any of a number of desired types (e.g., data, video, speech, audio, etc. any of which may generally be referred to as ‘data’).

[0051] 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) “configured to”, “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 an example of 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 “configured to”, “operable to”, “coupled 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.

[0052] 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. As may be used herein, the term “compares unfavorably”, indicates that a comparison between two or more items, signals, etc., fails to provide the desired relationship.

[0053] As may also be used herein, the terms “processing module”, “processing circuit”, “processor”, and/or “processing unit” 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, module, processing circuit, and/or processing unit may be, or further include, memory and/or an integrated memory element, which may be a single memory device, a plurality of memory devices, and/or embedded circuitry of another processing module, module, processing circuit, and/or processing unit. 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, module, processing circuit, and/or processing unit 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 if the processing module, module, processing circuit, and/or processing unit 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 may store, and the processing module, module, processing circuit, and/or processing unit executes, hard coded and/or operational instructions corresponding to at least some of the steps and/or functions illustrated in one or more of the Figures. Such a memory device or memory element can be included in an article of manufacture.

[0054] One or more embodiments have 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 claims. Further, 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.

[0055] 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 claims. 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.

[0056] In addition, a flow diagram may include a “start” and/or “continue” indication. The “start” and “continue” indications reflect that the steps presented can optionally be incorporated in or otherwise used in conjunction with other routines. In this context, “start” indicates the beginning of the first step presented and may be preceded by other activities not specifically shown. Further, the “continue” indication reflects that the steps presented may be performed multiple times and/or may be succeeded by other activities not specifically shown. Further, while a flow diagram indicates a particular ordering of steps, other orderings are likewise possible provided that the principles of causality are maintained.

[0057] The one or more embodiments are used herein to illustrate one or more aspects, one or more features, one or more concepts, and/or one or more examples. A physical embodiment of an apparatus, an article of manufacture, a machine, and/or of a process may include one or more of the aspects, features, concepts, examples, etc. described with reference to one or more of the embodiments discussed herein. Further, from figure to figure, the embodiments may incorporate the same or similarly named functions, steps, modules, etc. that may use the same or different reference numbers and, as such, the functions, steps, modules, etc. may be the same or similar functions, steps, modules, etc. or different ones.

[0058] Unless specifically stated to the contra, signals to, from, and/or between elements in a figure of any of the figures presented herein may be analog or digital, continuous time or discrete time, and single-ended or differential. For instance, if a signal path is shown as a single-ended path, it also represents a differential signal path. Similarly, if a signal path is shown as a differential path, it also represents a single-ended signal path. While one or more particular architectures are described herein, other architectures can likewise be implemented that use one or more data buses not expressly shown, direct connectivity between elements, and/or indirect coupling between other elements as recognized by one of average skill in the art.

[0059] The term “module” is used in the description of one or more of the embodiments. A module implements one or more functions via a device such as a processor or other processing device or other hardware that may include or operate in association with a memory that stores operational instructions. A module may operate independently and/or in conjunction with software and/or firmware. As also used herein, a module may contain one or more sub-modules, each of which may be one or more modules.

[0060] As may further be used herein, a computer readable memory includes one or more memory elements. A memory element may be a separate memory device, multiple memory devices, or a set of memory locations within a memory device. 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. The memory device may be in a form a solid state memory, a hard drive memory, cloud memory, thumb drive, server memory, computing device memory, and/or other physical medium for storing digital information.

[0061] While particular combinations of various functions and features of the one or more embodiments have been expressly described herein, other combinations of these features and functions are likewise possible. The present disclosure is not limited by the particular examples disclosed herein and expressly incorporates these other combinations.