Ensuring data integrity on a dispersed storage grid

• US 9,996,413 B2
• Filed: 10/09/2007
• Issued: 06/12/2018
• Est. Priority Date: 10/09/2007
• Status: Active Grant

• Current Assignee: Pure Storage, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Dhuse, Greg, Thornton, Vance, Resch, Jason, Volvovski, Ilya, Hendrickson, Dusty, Quigley, John
• Primary Examiner(s): GUYTON, PHILIP A
• Application Number:
  US11/973,542
• Publication Number:
  US 20090094250A1
• Time in Patent Office: 3,899 Days
• Field of Search: 714 6, 711153, 709215, 707693
• CPC Class Codes: G06F 11/1004 to protect a block of data words, e.g. CRC or checksum G06F11/1076 takes precedence; security arrangements for protecting computers or computer systems against unauthorized activity G06F21/00
• CPC Class Codes: G06F 11/1076 Parity data used in redundant arrays of independent storages, e.g. in RAID systems
• CPC Class Codes: G06F 2211/1088 Scrubbing in RAID systems with parity

Abstract

An improved system is disclosed for ensuring the integrity of data stored on a dispersed data storage network. Checksums are used to ensure integrity of both data segments and data slices. Checksums appended to data slices are checked by receiving slice servers to ensure that no errors occurred during transmission. Slice servers also periodically recalculate checksums for stored data slices to ensure that data slices have not been corrupted during storage. Checksums appended to data segments are checked when data segments are read from the storage network.

Claims

1. A method of ensuring data integrity in a dispersed data storage network, the method comprising:

calculating a first checksum for a data segment of data;

appending the first checksum to the data segment to produce an appended data segment;

encoding the appended data segment to produce a set of encoded data slices, wherein each encoded data slice of the set of encoded data slices includes an encoded representation of at least a portion of the first checksum;

generating a set of second checksums for the set of encoded data slices;

appending the set of second checksums to the set of encoded data slices to produce a set of appended encoded data slices; and

transmitting the set of appended encoded data slices to a plurality of storage units for storage therein;

when the data segment is to be reconstructed;

retrieving from the plurality of storage units a threshold number of appended encoded data slices of the set of appended encoded data slices;

extracting the threshold number of second checksums from the threshold number of appended encoded data slices; and

verifying accuracy of the threshold number of appended encoded data slices based on the extracted threshold number of second checksums; and

when verifying the accuracy of the threshold number of appended encoded data slices indicates that the threshold number of appended encoded data slices includes a corrupted appended encoded data slice therein;

retrieving from at least some of the plurality of storage units a sufficient number of appended encoded data slices needed to generate a reconstructed data segment based on the threshold number of appended encoded data slices that includes the corrupted appended encoded data slice;

generating the reconstructed data segment using the sufficient number of appended encoded data slices;

performing an error correcting information dispersal algorithm on the reconstructed data segment thereby forming a reconstructed set of data slices;

calculating a plurality of second checksums for the reconstructed set of data slices;

appending the plurality of second checksums respectively to the reconstructed set of data slices thereby forming a reconstructed set of appended encoded data slices; and

replacing the corrupted appended encoded data slice with a reconstructed appended encoded data slice of the reconstructed set of appended encoded data slices; and

when the accuracy of the threshold number of appended encoded data slices has been verified;

decoding the threshold number of appended encoded data slices to recover the appended data segment;

extracting the first checksum from the recovered appended data segment;

verifying accuracy of the recovered appended data segment based on the first checksum; and

when the accuracy of the recovered appended data segment has been verified, providing the recovered appended data segment as a valid data segment.

2. The method of claim 1 further comprising:

performing an integrity check on the set of appended encoded data slices stored within the plurality of storage units based on at least one of the set of second checksums or the first checksum;

identifying a corrupted appended encoded data slice within the set of appended encoded data slices based on the integrity checks;

generating a reconstructed set of appended encoded data slices corresponding to the set of appended encoded data slices; and

replacing the corrupted appended encoded data slice with one of the reconstructed appended encoded data slices from the reconstructed set of appended encoded data slices.

3. The method of claim 1 further comprising:

after transmitting the set of appended encoded data slices to the plurality of storage units to be stored therein, determining successful storage of the set of appended encoded data slices based on the at least the threshold number of appended encoded data slices from the set of appended encoded data slices needed respectively to reconstruct the set of appended encoded data slices being stored among the plurality of storage units.

4. The method of claim 1, wherein at least one of the first checksum or the set of second checksums is based on a cyclic redundancy check.

5. The method of claim 1, wherein the encoding of the appended data segment to produce the set of encoded data slices includes at least one of Reed-Solomon coding or Cauchy Reed-Solomon coding.

6. The method of claim 1, wherein a first of the plurality of storage units is remotely located from a second of the plurality of storage units within the dispersed data storage network.

7. A computer comprising:

a port configured to support communications with a dispersed data storage network;

an application, coupled to the port, that is configured to enable a computer to;

calculate a first checksum for a data segment of data;

append the first checksum to the data segment to produce an appended data segment;

encode the appended data segment to produce a set of encoded data slices, wherein each encoded data slice of the set of encoded data slices includes an encoded representation of at least a portion of the first checksum;

generate a set of second checksums for the set of encoded data slices;

append the set of second checksums to the set of encoded data slices to produce a set of appended encoded data slices; and

transmit the set of appended encoded data slices to a plurality of storage units for storage therein; and

when the data segment is to be reconstructed;

identify whether a threshold number of appended encoded data slices includes a corrupted appended encoded data slice therein; and

when the threshold number of appended encoded data slice includes the corrupted appended encoded data slice;

retrieve, from at least some of a plurality of storage units of the dispersed data storage network, a sufficient number of appended encoded data slices needed to generate a reconstructed data segment based on the threshold number of appended encoded data slices that includes the corrupted appended encoded data slice;

generate the reconstructed data segment using the sufficient number of appended encoded data slices;

perform an error correcting information dispersal algorithm on the reconstructed data segment thereby forming a reconstructed set of data slices;

calculating a plurality of second checksums for the reconstructed set of data slices;

append the plurality of second checksums respectively to the reconstructed set of data slices thereby forming a reconstructed set of appended encoded data slices; and

replace the corrupted appended encoded data slice with one of the reconstructed set of appended encoded data slices.

8. The computer of claim 7, wherein the application, coupled to the port, is further configured to enable the computer to:

retrieve from the plurality of storage units a threshold number of appended encoded data slices of the set of appended encoded data slices;

extract the threshold number of second checksums from the threshold number of appended encoded data slices;

verify accuracy of the threshold number of appended encoded data slices based on the extracted threshold number of second checksums;

when the accuracy of the threshold number of appended encoded data slices has been verified;

decode the threshold number of appended encoded data slices to recover the appended data segment;

extract the first checksum from the recovered appended data segment;

verify accuracy of the recovered appended data segment based on the first checksum; and

when the accuracy of the recovered appended data segment has been verified, providing the recovered appended data segment as a valid data segment.

9. The computer of claim 7, wherein the application, coupled to the port, is further configured to enable the computer to:

after transmitting the set of appended encoded to the plurality of storage units to be stored therein, determine successful storage of the set of appended encoded based on the at least the threshold number of appended encoded data slices.

10. The computer of claim 7 further comprising:

a grid computer that is coupled to the plurality of storage units via the dispersed data storage network.

11. The computer of claim 7, wherein the encoding of the appended data segment to produce the set of encoded data slices includes at least one of Reed-Solomon coding or Cauchy Reed-Solomon coding.

12. The computer of claim 7, wherein:

a first of the plurality of storage units is remotely located from a second of the plurality of storage units within the dispersed data storage network; and

at least one of the first of the plurality of storage units or the second of the plurality of storage units is remotely located from the computer within the dispersed data storage network.

13. A computer comprising:

a port configured to support communications with a dispersed data storage network;

an application, coupled to the port, that is configured to enable a computer to;

when a data segment is to be reconstructed;

retrieving, from a plurality of storage units of the dispersed data storage network, a threshold number of appended encoded data slices of a set of appended encoded data slices;

extracting a threshold number of second checksums from the threshold number of appended encoded data slices; and

verifying accuracy of the threshold number of appended encoded data slices based on the extracted threshold number of second checksums;

when the threshold number of appended encoded data slices includes a corrupted appended encoded data slice therein;

retrieve, from at least some of the plurality of storage units, a sufficient number of appended encoded data slices needed to generate a reconstructed data segment based on the threshold number of appended encoded data slices that includes the corrupted appended encoded data slice;

generate the reconstructed data segment using the sufficient number of appended encoded data slices;

perform an error correcting information dispersal algorithm on the reconstructed data segment thereby forming a reconstructed set of data slices;

calculating a plurality of second checksums for the reconstructed set of data slices;

append the plurality of second checksums respectively to the reconstructed set of data slices thereby forming a reconstructed set of appended encoded data slices; and

replace the corrupted appended encoded data slice with one of the reconstructed set of appended encoded data slices; and

when the accuracy of the threshold number of appended encoded data slices has been verified;

decoding the threshold number of appended encoded data slices to recover the appended data segment;

extracting the first checksum from the recovered appended data segment;

verifying accuracy of the recovered appended data segment based on the first checksum; and

when the accuracy of the recovered appended data segment has been verified, providing the recovered appended data segment as a valid data segment.

14. The computer of claim 13, wherein the application, coupled to the port, is further configured to enable the computer to:

perform an integrity check on the set of appended encoded data slices stored within the plurality of storage units based on at least one of the set of second checksums or the first checksum;

identify a corrupted certified data slice within a set of appended encoded data slices based on the integrity check;

generate a reconstructed set of appended encoded data slices corresponding to the set of appended encoded data slices; and

replace the corrupted appended encoded data slice with one of the reconstructed set of appended encoded data slices.

15. The computer of claim 13 further comprising:

a grid computer that is coupled to the plurality of storage units via the dispersed data storage network.

16. The computer of claim 13, wherein the encoding of the appended data segment to produce the set of encoded data slices includes at least one of Reed-Solomon coding or Cauchy Reed-Solomon coding.

17. The computer of claim 13, wherein:

a first of the plurality of storage units is remotely located from a second of the plurality of storage units within the dispersed data storage network; and

at least one of the first of the plurality of storage units or the second of the plurality of storage units is remotely located from the computer within the dispersed data storage network.