WEAR LEVELING OF SOLID STATE DISKS DISTRIBUTED IN A PLURALITY OF REDUNDANT ARRAY OF INDEPENDENT DISK RANKS

• US 20100332749A1
• Filed: 06/30/2009
• Published: 12/30/2010
• Est. Priority Date: 06/30/2009
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Walls, Andrew Dale, Benhase, Michael Thomas
• Granted Patent: US 8,639,877 B2
• Time in Patent Office: Days
• US Class Current: 711/114
• CPC Class Codes: G06F 11/108 Parity data distribution in semiconductor storages, e.g. in SSD
• CPC Class Codes: G06F 11/1096 Parity calculation or recalculation after configuration or reconfiguration of the system
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/7208 Multiple device management, e.g. distributing data over multiple flash devices
• CPC Class Codes: G06F 2212/7211 Wear leveling

Abstract

A computational device allocates a plurality of solid state disks to a plurality of redundant array of independent disk (RAID) ranks, wherein a different solid state disk is absent in each RAID rank of the plurality of RAID ranks. The computational device determines at least one selected solid state disk from the plurality of solid state disks, wherein the at least one selected solid state disk is estimated to have undergone a greater amount of wear in comparison to other solid state disks in the plurality of solid state disks. Relatively more data and parity information is written to those RAID ranks in which the at least one selected solid state disk is absent in comparison to those RAID ranks in which the at least one selected solid state disk is present.

Claims

1. A method, comprising:

allocating, by a computational device, a plurality of solid state disks to a plurality of redundant array of independent disk (RAID) ranks, wherein a different solid state disk is absent in each RAID rank of the plurality of RAID ranks;

determining, by the computational device, at least one selected solid state disk from the plurality of solid state disks, wherein the at least one selected solid state disk is estimated to have undergone a greater amount of wear in comparison to other solid state disks in the plurality of solid state disks; and

writing, by the computational device, relatively more data and parity information to those RAID ranks in which the at least one selected solid state disk is absent in comparison to those RAID ranks in which the at least one selected solid state disk is present.

2. The method of claim 1, wherein:

the allocated solid state disks in each RAID rank are fewer in number than the plurality of solid state disks; and

each solid state disk of the plurality of solid state disks is shared by more than one RAID rank.

3. The method of claim 2, further comprising:

performing distributed sparing by preferentially allocating spare space on those solid state disks that are estimated to have undergone a greater amount of wear in comparison to other solid state disks in the plurality of solid state disks.

4. The method of claim 3, wherein:

in response to the plurality of solid state disks being allocated in a log structured array, adding metadata to an index of the log structured array, wherein in log structured arrays each write is performed without any overwriting of previously performed writes; and

in response to the plurality of solid state disks being allocated as home area storage systems, rotating RAID ranks based on stripe number.

5. The method of claim 3, wherein the plurality of RAID ranks and the plurality of solid state disks are same in number, wherein each RAID rank has one less solid state disk than the plurality of solid state disks, and wherein the method further comprises:

maintaining a first indicator corresponding to each RAID rank, wherein the first indicator indicates the amount of data and parity to be written to a corresponding RAID rank;

maintaining a second indicator corresponding to each solid state disk, wherein the second indicator indicates an amount of wear undergone by a corresponding solid state disk; and

maintaining a data structure that indicates an adjustment to be made to a value stored in the first indicator based on differences in second indicator values of the plurality of solid state disks.

6. The method of claim 1, wherein the at least one selected solid state disk is a first solid state disk, the method further comprising:

determining, by the computational device, a second solid state disk from the plurality of solid state disks, wherein the second solid state disk is estimated to have a lesser amount of life left in comparison to other solid state disks in the plurality of solid state disks; and

writing relatively more data and parity information to those RAID ranks in which the second selected solid state disk is absent in comparison to those RAID ranks in which the second solid state disk is present.

7. The method of claim 1, wherein the computational device is a RAID controller, and wherein the plurality of solid state disks are operatively coupled to the RAID controller.

8. A controller for configuring a plurality of solid state disks, the controller comprising:

a memory; and

a processor coupled to the memory, wherein the processor performs operations, the operations comprising;

allocating the plurality of solid state disks to a plurality of redundant array of independent disk (RAID) ranks, wherein a different solid state disk is absent in each RAID rank of the plurality of RAID ranks;

determining at least one selected solid state disk from the plurality of solid state disks, wherein the at least one selected solid state disk is estimated to have undergone a greater amount of wear in comparison to other solid state disks in the plurality of solid state disks; and

writing relatively more data and parity information to those RAID ranks in which the at least one selected solid state disk is absent in comparison to those RAID ranks in which the at least one selected solid state disk is present.

9. The controller of claim 8, wherein:

the allocated solid state disks in each RAID rank are fewer in number than the plurality of solid state disks; and

each solid state disk of the plurality of solid state disks is shared by more than one RAID rank.

10. The controller of claim 9, the operations further comprising:

performing distributed sparing by preferentially allocating spare space on those solid state disks that are estimated to have undergone a greater amount of wear in comparison to other solid state disks in the plurality of solid state disks.

11. The controller of claim 10, wherein:

in response to the plurality of solid state disks being allocated in a log structured array, adding metadata to an index of the log structured array, wherein in log structured arrays each write is performed without any overwriting of previously performed writes; and

in response to the plurality of solid state disks being allocated as home area storage systems, rotating RAID ranks based on stripe number.

12. The controller of claim 10, wherein the plurality of RAID ranks and the plurality of solid state disks are same in number, wherein each RAID rank has one less solid state disk than the plurality of solid state disks, and wherein the operations further comprise:

maintaining a first indicator corresponding to each RAID rank, wherein the first indicator indicates the amount of data and parity to be written to a corresponding RAID rank;

maintaining a second indicator corresponding to each solid state disk, wherein the second indicator indicates an amount of wear undergone by a corresponding solid state disk; and

maintaining a data structure that indicates an adjustment to be made to a value stored in the first indicator based on differences in second indicator values of the plurality of solid state disks.

13. The controller of claim 8, wherein the at least one selected solid state disk is a first solid state disk, the operations further comprising:

determining, a second solid state disk from the plurality of solid state disks, wherein the second solid state disk is estimated to have a lesser amount of life left in comparison to other solid state disks in the plurality of solid state disks; and

writing relatively more data and parity information to those RAID ranks in which the second selected solid state disk is absent in comparison to those RAID ranks in which the second solid state disk is present.

14. The controller of claim 8, wherein the controller is a RAID controller, and wherein the plurality of solid state disks are operatively coupled to the RAID controller.

15. A computer program product for wear leveling of a plurality of solid state disks, the computer program product comprising:

a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code configured to;

allocate the plurality of solid state disks to a plurality of redundant array of independent disk (RAID) ranks, wherein a different solid state disk is absent in each RAID rank of the plurality of RAID ranks;

determine at least one selected solid state disk from the plurality of solid state disks, wherein the at least one selected solid state disk is estimated to have undergone a greater amount of wear in comparison to other solid state disks in the plurality of solid state disks; and

write relatively more data and parity information to those RAID ranks in which the at least one selected solid state disk is absent in comparison to those RAID ranks in which the at least one selected solid state disk is present.

16. The computer program product of claim 15, wherein:

the allocated solid state disks in each RAID rank are fewer in number than the plurality of solid state disks; and

each solid state disk of the plurality of solid state disks is shared by more than one RAID rank.

17. The computer program product of claim 16, wherein the computer readable program code is further configured to:

perform distributed sparing by preferentially allocating spare space on those solid state disks that are estimated to have undergone a greater amount of wear in comparison to other solid state disks in the plurality of solid state disks.

18. The computer program product of claim 17, wherein:

in response to the plurality of solid state disks being allocated in a log structured array, adding metadata to an index of the log structured array, wherein in log structured arrays each write is performed without any overwriting of previously performed writes; and

in response to the plurality of solid state disks being allocated as home area storage systems, rotating RAID ranks based on stripe number.

19. The computer program product of claim 17, wherein the plurality of RAID ranks and the plurality of solid state disks are same in number, wherein each RAID rank has one less solid state disk than the plurality of solid state disks, and wherein the computer readable program code is further configured to:

maintain a first indicator corresponding to each RAID rank, wherein the first indicator indicates the amount of data and parity to be written to a corresponding RAID rank;

maintain a second indicator corresponding to each solid state disk, wherein the second indicator indicates an amount of wear undergone by a corresponding solid state disk; and

maintain a data structure that indicates an adjustment to be made to a value stored in the first indicator based on differences in second indicator values of the plurality of solid state disks.

20. The computer program product of claim 15, wherein the at least one selected solid state disk is a first solid state disk, wherein the computer readable program code is further configured to:

determine, a second solid state disk from the plurality of solid state disks, wherein the second solid state disk is estimated to have a lesser amount of life left in comparison to other solid state disks in the plurality of solid state disks; and

write relatively more data and parity information to those RAID ranks in which the second selected solid state disk is absent in comparison to those RAID ranks in which the second solid state disk is present.