Methods and systems for reducing churn in flash-based cache

• US 9,081,670 B2
• Filed: 05/08/2014
• Issued: 07/14/2015
• Est. Priority Date: 07/14/2010
• Status: Active Grant

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: Nimble Storage (Hewlett-Packard Enterprise Company)
• Inventors: Maheshwari, Umesh, Mehta, Varun
• Primary Examiner(s): MACKALL, LARRY T
• Application Number:
  US14/273,367
• Publication Number:
  US 20140244917A1
• Time in Patent Office: 432 Days
• Field of Search: 711/113, 711/103, 711/138
• US Class Current: 1/1
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 12/0888 using selective caching, e.g. bypass
• CPC Class Codes: G06F 2212/1036 Life time enhancement
• CPC Class Codes: G06F 2212/1044 Space efficiency improvement
• CPC Class Codes: G06F 2212/222 Non-volatile memory
• CPC Class Codes: G06F 2212/28 Using a specific disk cache architecture
• CPC Class Codes: G06F 2212/466 Metadata, control data
• CPC Class Codes: G06F 2212/60 Details of cache memory
• CPC Class Codes: G06F 2212/604 Details relating to cache allocation
• CPC Class Codes: G06F 2212/7202 Allocation control and policies
• CPC Class Codes: G06F 2212/7205 Cleaning, compaction, garbage collection, erase control
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/0685 Hybrid storage combining heterogeneous device types, e.g. hierarchical storage, hybrid arrays

Abstract

A storage device includes a flash memory-based cache for a hard disk-based storage device and a controller that is configured to limit the rate of cache updates through a variety of mechanisms, including determinations that the data is not likely to be read back from the storage device within a time period that justifies its storage in the cache, compressing data prior to its storage in the cache, precluding storage of sequentially-accessed data in the cache, and/or throttling storage of data to the cache within predetermined write periods and/or according to user instruction.

Claims

1. A method, comprising:

receiving data to be stored in a storage device having a flash memory-based cache and a disk-based storage unit;

writing an initial portion of the data to the flash memory-based cache and the disk-based storage unit;

while the initial portion is being written to the flash memo-based cache and the disk-based storage unit, monitoring an amount of the initial portion that has been written sequentially;

determining whether the amount that has been written sequentially exceeds a predetermined threshold beyond which the data can be read from the flash memory-based cache at a substantially similar data rate as from the disk-based storage unit; and

if so, determining that the data will likely be sequentially accessed, ceasing writing of the data to the flash memory-based cache and writing the remaining portion of the data only to the disk-based storage unit so as to reduce the amount of data written to the flash memory-based cache.

2. The method of claim 1, wherein the received data comprises compressed data.

3. The method of claim 1, further comprising throttling updates to the flash memory-based cache by permitting only a threshold number of writes per write period to the flash memory-based cache, wherein each write period comprises a period of fixed interval.

4. The method of claim 3, wherein the updates to the flash memory-based cache are throttled in accordance with user instructions concerning whether or not the data is to be cached.

5. The method of claim 1, further comprising compressing the data prior to writing the data to the flash memory-based cache, said compressing producing variable sized blocks of data.

6. The method of claim 1, further comprising throttling updates to the flash memory-based cache in accordance with user instructions concerning a data type of the data.

7. A storage device, comprising a flash memory-based cache;

a disk-based storage unit; and

a controller communicatively coupled to the flash memory-based cache and the disk-based storage unit, the controller configured to;

receive data to be stored in the storage device;

write an initial portion of the data to the flash memory-based cache and the disk-based storage unit;

while the initial portion is being written to the flash memo-based cache and the disk-based storage unit, monitor an amount of the initial portion that has been written sequentially;

determine whether the amount that has been written sequentially exceeds a predetermined threshold beyond which the data can be read from the flash memory-based cache at a substantially similar data rate as from the disk-based storage unit; and

if so, determine that the data will likely be sequentially accessed, cease writing of the data to the flash memory-based cache and write the remaining portion of the data only to the disk-based storage unit so as to reduce the amount of data written to the flash memory-based cache.

8. The storage device of claim 7, wherein the controller is further configured to compress the received data prior to writing the compressed data to the flash memory-based cache.

9. The storage device of claim 7, wherein the controller is further configured to throttle updates to the flash memory-based cache by permitting only a threshold number of writes per write period to the flash memory-based cache, wherein each write period comprises a period of fixed interval.

10. The storage device of claim 7, wherein the controller is further configured to throttle updates to the flash memory-based cache in accordance with user instructions concerning whether or not the data is to be cached.

11. The storage device of claim 7, wherein the controller is further configured to throttle updates to the flash memory-based cache in accordance with user instructions concerning a data type of the data.

12. A non-transitory computer-readable storage medium including a set of instructions stored thereon, which when executed by a storage device cause the storage device to:

receive data to be stored in the storage device, the storage device having a flash memory-based cache and a disk-based storage unit;

write an initial portion of the data to the flash memory-based cache and the disk-based storage unit;

while the initial portion is being written to the flash memo-based cache and the disk-based storage unit, monitor an amount of the initial portion that has been written sequentially;

determine whether the amount that has been written sequentially exceeds a predetermined threshold beyond which the data can be read from the flash memory-based cache at a substantially similar data rate as from the disk-based storage unit; and

if so, determine that the data will likely be sequentially accessed, cease writing of the data to the flash memory-based cache and write the remaining portion of the data only to the disk-based storage unit so as to reduce the amount of data written to the flash memory-based cache.

13. The non-transitory computer-readable storage medium of claim 12, further including instructions, which when executed by the storage device cause the storage device to compress the received data prior to writing the compressed data to the flash memory-based cache.

14. The non-transitory computer-readable storage medium of claim 12, further including instructions, which when executed by the storage device cause the storage device to throttle updates to the flash memory-based cache by permitting only a threshold number of writes per write period to the flash memory-based cache, wherein each write period comprises a period of fixed interval.

15. The non-transitory computer-readable storage medium of claim 12, further including instructions, which when executed by the storage device cause the storage device to throttle updates to the flash memory-based cache in accordance with user instructions concerning whether or not the data is to be cached.

16. The non-transitory computer-readable storage medium of claim 12, further including instructions, which when executed by the storage device cause the storage device to throttle updates to the flash memory-based cache in accordance with user instructions concerning a data type of the data.