METHOD AND APPARATUS FOR PROTECTING THE INTEGRITY OF CACHED DATA IN A DIRECT-ATTACHED STORAGE (DAS) SYSTEM

• US 20100312960A1
• Filed: 06/04/2010
• Published: 12/09/2010
• Est. Priority Date: 06/08/2009
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: LSI Corporation (Broadcom, Inc.)
• Inventors: Bert, Luca
• Granted Patent: US 8,732,396 B2
• Time in Patent Office: Days
• US Class Current: 711/113
• CPC Class Codes: G06F 11/1008 in individual solid state devices G06F11/1004 takes precedence
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/084 with a shared cache
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 2212/222 Non-volatile memory
• CPC Class Codes: G06F 2212/262 configured as RAID

Abstract

A DAS system that implements RAID technology is provided in which an array of solid state disks (SSDs) that is external to the DAS controllers of the DAS system is used by the DAS controllers as WB cache memory for performing WB caching operations. Using the external SSD array as WB cache memory allows the DAS system to be fully cache coherent without significantly increasing the complexity of the DAS system and without increasing the amount of bandwidth that is utilized for performing caching operations. In addition, using the external SSD array as WB cache memory obviates the need to mirror DAS controllers.

Claims

1. A direct-attached storage (DAS) system comprising:

a plurality of magnetic hard disk drives (HDDs) configured as a Redundant Array of Inexpensive (or Independent) Disks (RAID) array of physical disk drives (PDs);

an array of solid state disks (SSDs) configured as cache memory; and

at least first and second DAS controllers connected to the RAID array of PDs and to the SSD array, each DAS controller having a central processing unit (CPU), a local memory device, and an input/output (I/O) interface device, wherein each of the CPUs and each of the local memory devices is configured to perform a RAID level of technology consistent with the RAID configuration of the RAID array of PDs, and wherein each of the CPUs is configured to perform a caching algorithm that causes data received in the respective DAS controller to be temporarily stored in the cache memory of the SSD array and subsequently stored in one or more of the PDs of the RAID array of PDs.

2. The DAS system of claim 1, wherein the caching algorithm is a write back (WB) caching algorithm that WB caches the data in the cache memory of the SSD array prior to storing the data in one or more of the PDs of the RAID array of PDs.

3. The DAS system of claim 2, wherein the data has metadata associated therewith, and wherein each of the local memory devices of the DAS controllers has a portion thereof that is used as cache memory, and wherein the WB caching algorithm performed by the respective CPUs cause the metadata associated with the data received in the respective DAS controller to be temporarily stored in the respective cache memory portion of the respective local memory device and subsequently stored in one or more of the PDs of the RAID array of PDs.

4. The DAS system of claim 2, wherein the data has metadata associated therewith, and wherein the WB caching algorithm performed by the respective CPUs cause the metadata associated with the data received in the respective DAS controller to be temporarily stored in the cache memory of the SSD array and subsequently stored in one or more of the PDs of the RAID array of PDs.

5. The DAS system of claim 1, wherein the respective CPUs are configured to perform a level of RAID technology with respect to the temporary storage of data in the SSD array such that cache coherency is provided for the data that is temporarily stored in the SSD array.

6. The DAS system of claim 5, wherein the data has metadata associated therewith, and wherein the caching algorithm performed by the respective CPUs cause the data be stored in blocks in the SSD array, each block including a data integrity field (DIF), and wherein the respective CPUs cause the metadata associated with the data received in the respective DAS controller to be stored in at least one of the DIFs associated with at least one of the blocks in which the associated data is stored in the SSD array.

7. The DAS system of claim 6, wherein the caching algorithm performed by each respective CPU includes a hashing algorithm that calculates a hash of the metadata, and wherein each respective hash is stored in said at least one of the DIFs associated with at least one of the blocks in which the associated data is stored in the SSD array.

8. The DAS system of claim 6, wherein the metadata associated with the data includes an indication of a source of the data, an indication of a length of the data, and an indication of whether or not the data has been modified.

9. A method for protecting the integrity of cached data in a direct-attached storage (DAS) system, the method comprising:

in a first DAS controller, receiving data, the first DAS controller including a central processing unit (CPU), a local memory device, and an input/output (I/O) interface device;

in the CPU of the first DAS controller, performing a caching algorithm that causes the data received in the first DAS controller to be temporarily stored in one or more solid state disks (SSDs) of an SSD array and subsequently stored in one or more magnetic hard disk drives (HDDs) configured as a Redundant Array of Inexpensive (or Independent) Disks (RAID) array of physical disk drives (PDs);

in a second DAS controller, receiving data, the second DAS controller including a CPU, a local memory device, and an I/O interface device; and

in the CPU of the second DAS controller, performing a caching algorithm that causes the data received in the second DAS controller to be temporarily stored in one or more SSDs of the SSD array and subsequently stored in one or more of the magnetic HDDs configured as the RAID array of PDs.

10. The method of claim 9, wherein the caching algorithm is a write back (WB) caching algorithm that WB caches the data in the cache memory of the SSD array prior to storing the data in one or more of the PDs of the RAID array of PDs.

11. The method of claim 10, wherein the data has metadata associated therewith, and wherein each of the local memory devices of the DAS controllers has a portion thereof that is used as cache memory, and wherein the WB caching algorithm performed by the respective CPUs cause the metadata associated with the data received in the respective DAS controller to be temporarily stored in the respective cache memory portion of the respective local memory device and subsequently stored in one or more of the PDs of the RAID array of PDs.

12. The method of claim 10, wherein the data has metadata associated therewith, and wherein the WB caching algorithm performed by the respective CPUs cause the metadata associated with the data received in the respective DAS controller to be temporarily stored in the cache memory of the SSD array and subsequently stored in one or more of the PDs of the RAID array of PDs.

13. The method of claim 9, wherein the respective CPUs are configured to perform a level of RAID technology with respect to the temporary storage of data in the SSD array such that cache coherency is provided for the data that is temporarily stored in the SSD array.

14. The method of claim 13, wherein the data has metadata associated therewith, and wherein the caching algorithm performed by the respective CPUs cause the data be stored in blocks in the SSD array, each block including a data integrity field (DIF), and wherein the respective CPUs cause the metadata associated with the data received in the respective DAS controller to be stored in at least one of the DIFs associated with at least one of the blocks in which the associated data is stored in the SSD array.

15. The method of claim 14, wherein the caching algorithm performed by each respective CPU includes a hashing algorithm that calculates a hash of the metadata, and wherein each respective hash is stored in said at least one of the DIFs associated with at least one of the blocks in which the associated data is stored in the SSD array.

16. The method of claim 14, wherein the metadata associated with the data includes an indication of a source of the data, an indication of a length of the data, and an indication of whether or not the data has been modified.

17. A computer-readable medium having a computer program stored thereon for protecting the integrity of cached data in a direct-attached storage (DAS) system, the computer program comprising computer instructions stored on the computer-readable medium, the instructions comprising:

a first set of instructions for receiving data in a first DAS controller; and

a second set of instructions for performing a caching algorithm in the first DAS controller that causes the data received in the first DAS controller to be temporarily stored in one or more solid state disks (SSDs) of an SSD array and subsequently stored in one or more magnetic hard disk drives (HDDs) configured as a Redundant Array of Inexpensive (or Independent) Disks (RAID) array of physical disk drives (PDs).

18. The computer-readable medium of claim 17, wherein the caching algorithm is a write back (WB) caching algorithm that WB caches the data in the cache memory of the SSD array prior to storing the data in one or more of the PDs of the RAID array of PDs.

19. The computer-readable medium of claim 17, wherein the data has metadata associated therewith, and wherein the caching algorithm causes the metadata associated with the data received in the DAS controller to be temporarily stored in a cache memory portion of a local memory device of the DAS controller and subsequently stored in one or more of the PDs of the RAID array of PDs.

20. The computer-readable medium of claim 17, wherein the data has metadata associated therewith, and wherein the caching algorithm causes the metadata associated with the data received in the DAS controller to be temporarily stored in the cache memory of the SSD array and subsequently stored in one or more of the PDs of the RAID array of PDs.

21. The computer-readable medium of claim 17, wherein the DAS controller is configured to perform a level of RAID technology with respect to the temporary storage of data in the SSD array such that cache coherency is provided for the data that is temporarily stored in the SSD array.

22. The computer-readable medium of claim 21, wherein the data has metadata associated therewith, and wherein the caching algorithm performed by the DAS controller causes the data be stored in blocks in the SSD array, each block including a data integrity field (DIF), and wherein the DAS controller causes the metadata associated with the data received in the respective DAS controller to be stored in at least one of the DIFs associated with at least one of the blocks in which the associated data is stored in the SSD array.

23. The computer-readable medium of claim 22, wherein the caching algorithm performed by the DAS controller includes a hashing algorithm that calculates a hash of the metadata, and wherein each respective hash is stored in said at least one of the DIFs associated with at least one of the blocks in which the associated data is stored in the SSD array.

24. The computer-readable medium of claim 22, wherein the metadata associated with the data includes an indication of a source of the data, an indication of a length of the data, and an indication of whether or not the data has been modified.