Techniques for caching data using a volatile memory cache and solid state drive

• US 9,081,691 B1
• Filed: 09/21/2012
• Issued: 07/14/2015
• Est. Priority Date: 06/29/2007
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Gupta, Uday K., Hopkins, Charles H., Evans, Michael B.
• Primary Examiner(s): Li, Aimee
• Assistant Examiner(s): SIMONETTI, NICHOLAS J
• Application Number:
  US13/624,098
• Time in Patent Office: 1,026 Days
• Field of Search: 711/103, 711117-122, 711/129, 711161-162, 711/173
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0815 Cache consistency protocols
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 12/0891 using clearing, invalidating or resetting means
• CPC Class Codes: G06F 2212/214 Solid state disk
• CPC Class Codes: G06F 2212/7202 Allocation control and policies
• CPC Class Codes: G06F 2212/7204 Capacity control, e.g. partitioning, end-of-life degradation

Abstract

Described are techniques for performing recovery processing in a data storage system. A providing a flash-based memory is provided with includes cached write data that has not been destaged to a data storage device. It is determined whether said flash-based memory has a threshold amount of storage available thereon. If the flash-based memory does not have the threshold amount of storage available thereon, portions of the cache write data are destaged until said flash-based memory has a threshold amount of storage available thereon. Received data requests are processed in accordance with a first policy different from a second policy used in connection with processing received data requests if said flash-based memory has a threshold amount of storage available thereon.

Claims

1. A system comprising:

a volatile memory cache including cached write data that has not yet been destaged to a data storage device;

a solid state drive configured to include;

a first area that stores at least a portion of cached write data from the volatile memory cache, and a second area that, upon the occurrence of a vault operation event, stores all remaining portions of cached write data from the volatile memory cache not stored in the first area; and

a controller coupled to the volatile memory cache and the solid state drive, the controller being configured to;

operate in a first mode of normal processing of data requests in which cached write data is copied from a first portion of the volatile memory cache to the first area and not the second area, and then destaged from the first area to a data storage device, wherein the first portion of the volatile memory is designated as free and made available for another use once the cached write data of the first portion has been copied to the first area, and, operate in a second mode in which all remaining portions of cached write data from the volatile memory cache not currently included in the first area are copied to the second area upon the occurrence of a vault operation event, wherein the second area is a reserved portion of the solid state drive and is not used when operating in the first mode of normal processing of data requests;

receive a signal indicating a vault operation event; and

in response to receiving said signal, operate in said second mode.

2. The system of claim 1, further comprising a secondary power source, and wherein, if the vault operation event is a power failure of a primary power source, the secondary power source operates when in said second mode at least until the remaining portions are copied to said second area.

3. The system of claim 1, wherein one of said volatile memory or said solid state drive includes information indicating what portions of the cached write data in the volatile memory are stored in the solid state drive at a current point in time.

4. The system of claim 3, wherein when the controller is in the first mode, the controller is further configured to:

copy cached write data from the volatile memory cache to the first area;

update the information indicating what portions of the cached write data have been moved to the solid state drive in accordance with said copy; and

indicate as available for reuse a portion of the volatile memory cache including said cached write data copied to the first area.

5. The system of claim 4, wherein the information is stored in the volatile memory cache.

6. The system of claim 4, wherein the information is stored in the solid state drive.

7. The system of claim 4, wherein when the controller is in the first mode, the controller performs processing to copy the cached write data from the volatile memory cache to the first area and to update the information indicating what portions of the cached write data are stored in the solid state drive in accordance with said copy as a background process on a continuous basis.

8. The system of claim 7, wherein, if cached write data from the volatile memory cache has been moved to a target location in the solid state drive, the information includes an indicator indicating the target location as containing the cached write data to be destaged, and wherein an indicator is maintained for each chunk of solid state drive, said indicator being set when said each chunk includes cached write data moved from the volatile memory to be destaged, and is not set otherwise.

9. The system of claim 3, wherein, when the controller is in the second mode, the controller is further configured to:

copy all remaining cached write data from the volatile memory cache not currently in the first area to the second area;

store a version identifier identifying a version of the cached write data included in the solid state drive; and

update the information indicating what portions of the cached write data are stored in the solid state drive in accordance with said copy.

10. The system of claim 1, wherein said second area has a size larger than a size of said volatile memory cache.

11. The system of claim 1, wherein the system includes multiple storage processors, each of said multiple storage processors including an instance of said volatile memory, said solid state drive, and said controller local to said each storage processor.

12. A non-transitory computer readable medium comprising code stored thereon for caching data, the non-transitory computer readable medium comprising code stored thereon that, when executed, performs a method comprising:

configuring a solid state drive including a first area and a second area, wherein the first area is used to store at least a portion of cached write data from a volatile memory cache, said volatile memory cache including cached write data that has not yet been destaged to a data storage device, and wherein, upon the occurrence of a vault operation event, said second area is used to store all remaining portions of cached write data from the volatile memory cache not stored in the first area;

operating in a first mode of normal processing of data requests in which cached write data is copied from a first portion of the volatile memory cache to the first area and not the second area, and then destaged from the first area to a data storage device, wherein the first portion of the volatile memory is designated as free and made available for another use once the cached write data has been copied to the first area; and

in response to a vault operation event, operating in a second mode in which all remaining portions of cached write data from the volatile memory cache not currently included in the first area are copied to the second area, wherein the second area is a reserved portion of the solid state drive and is not used when operating in the first mode of normal processing of data requests.

13. A non-transitory computer readable medium comprising code stored thereon for managing data, the non-transitory computer readable medium comprising code stored thereon that, when executed, performs a method comprising:

while operating in a first mode of normal processing of data requests, copying portions of cached write data not yet destaged to a data storage device from a first portion of a volatile memory cache to a first area in a solid state drive and not a second area of the solid state drive, and then copying the portions of the cached write data from the first area to the data storage device, wherein the first portion of the volatile memory is designated as free and made available for another use once the cached write data of the first portion has been copied to the first area; and

in response to a vault operation event, operating in a second mode wherein all remaining portions of cached write data from the volatile memory cache not currently included in the first area are copied to a second area of the solid state drive, wherein when operating in the first mode, the first area is used and the second area is a reserved portion of the solid state drive and is not used when operating in the first mode of normal processing of data request.

14. The non-transitory computer readable medium of claim 13, wherein

the method further includes:

updating information indicating whether a portion of cached write data from the volatile memory cache is stored on the solid state drive after the cached write data is copied to the solid state drive.

15. The non-transitory computer readable medium of claim 14, wherein,

after a portion of the volatile memory cache is stored on the solid state drive, the information identifies a source location in the volatile memory cache including said portion as being available, and the information identifies a target location on the solid state drive at which the portion is stored as containing cached write data to be destaged.

16. The non-transitory computer readable medium of claim 14, wherein

the information is stored in the volatile memory.

17. The non-transitory computer readable medium of claim 14, wherein

the information is stored in the solid state drive.

18. The non-transitory computer readable medium of claim 14, wherein

the non-transitory computer readable medium further comprises code which, when in the first mode, performs processing including:

destaging cached write data from the solid state drive to a data storage device;

accordingly updating the information to indicate that the cached write data is no longer in the solid state drive.

19. The non-transitory computer readable medium of claim 13, wherein

the vault operation event is a primary power source failure, and a secondary power source supplies power for at least an amount of time required to copy remaining portions of cached write data from the volatile memory cache not currently included in the first area to the second area of the solid state drive.

20. The non-transitory computer readable medium of claim 13, wherein the copying portions of cached write data not yet destaged to a data storage device from the volatile memory cache to a first area in a solid state drive is performed as a background processing operation, and wherein the computer readable medium comprises code, that when executed, performs processing of the background processing operation including:

determining whether a threshold amount of storage is available on the solid state drive; and

flushing a portion of cached write data on the solid state drive to a data storage device if there is not a threshold amount available.