Methods and systems for throttling writes to a caching device in response to read misses

• US 9,665,495 B2
• Filed: 11/10/2016
• Issued: 05/30/2017
• 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: Mehta, Varun, Maheshwari, Umesh
• Primary Examiner(s): Mackall, Larry T
• Application Number:
  US15/347,963
• Publication Number:
  US 20170060763A1
• Time in Patent Office: 201 Days
• 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 for throttling cache updates in a storage system having a caching device and a storage device, the method comprising:

for each of a plurality of write periods of the storage system, each of the write periods having an associated threshold number of permitted writes to the caching device, receiving a request to read data that is stored on the storage system, and, upon determining that the requested data is stored on the storage device, but not on the caching device, then;

(i) if a number of writes to the caching device for the write period is less than or equal to the threshold number of permitted writes, reading the requested data from the storage device and storing the requested data in the caching device;

otherwise,

(ii) if the number of writes to the caching device for the write period is greater than the threshold number of permitted writes for the write period, reading the requested data from the storage device without storing the requested data in the caching device.

2. The method of claim 1, wherein the threshold number of permitted writes corresponding to each of the write periods is a fixed value.

3. The method of claim 1, wherein the threshold number of permitted writes corresponding to each of the write periods is updated periodically.

4. The method of claim 1, wherein the threshold number of permitted writes corresponding to each of the write periods is determined by dividing a number of writes that are permitted to the caching device during a remaining lifetime of the storage system by a number of write periods left in the remaining lifetime of the storage system.

5. The method of claim 1, wherein the requested data is compressed before being stored in the caching device.

6. The method of claim 1, wherein the caching device is configured with a log-structured file system, and the requested data is stored at an end of a log of the log-structured file system.

7. The method of claim 1, wherein the caching device is configured with a log-structured file system, and a compressed version of the requested data is stored at an end of a log of the log-structured file system.

8. A storage system, comprising a caching device, a storage device, and a storage controller communicatively coupled to the caching device and the storage device, the storage controller configured to:

for each of a plurality of write periods of the storage system, each of the write periods having an associated threshold number of permitted writes to the caching device, receive a request to read data that is stored on the storage system, and, upon determining that the requested data is stored on the storage device, but not on the caching device, then;

(i) if a number of writes to the caching device for the write period is less than or equal to the threshold number of permitted writes, read the requested data from the storage device and store the requested data in the caching device;

otherwise,

(ii) if the number of writes to the caching device for the write period is greater than the threshold number of permitted writes for the write period, read the requested data from the storage device without storing the requested data in the caching device.

9. The storage system of claim 8, wherein the caching device is a flash-based caching device.

10. The storage system of claim 8, wherein the storage device is a disk-based storage device.

11. The storage system of claim 8, wherein the caching device and the storage device are integrated together in a single device.

12. The storage system of claim 8, wherein the caching device and the storage device are two separate devices that are communicatively coupled to one another.

13. The storage system of claim 8, further comprising a host interface configured to communicatively couple the storage system to a host machine.

14. A non-transitory computer-readable storage medium comprising software instructions stored thereon for throttling cache updates in a storage system having a caching device and a storage device, wherein execution of the set of instructions by a controller of the storage system causes the controller to:

for each of a plurality of write periods of the storage system, each of the write periods having an associated threshold number of permitted writes to the caching device, receive a request to read data that is stored on the storage system, and, upon determining that the requested data is stored on the storage device, but not on the caching device, then;

(i) if a number of writes to the caching device for the write period is less than or equal to the threshold number of permitted writes, read the requested data from the storage device and store the requested data in the caching device;

otherwise,

(ii) if the number of writes to the caching device for the write period is greater than the threshold number of permitted writes for the write period, read the requested data from the storage device without storing the requested data in the caching device.

15. The non-transitory computer-readable storage medium of claim 14, wherein the threshold number of permitted writes corresponding to each of the write periods is a fixed value.

16. The non-transitory computer-readable storage medium of claim 14, wherein the threshold number of permitted writes corresponding to each of the write periods is updated periodically.

17. The non-transitory computer-readable storage medium of claim 14, wherein the threshold number of permitted writes corresponding to each of the write periods is determined by dividing a number of writes that are permitted to the caching device during a remaining lifetime of the storage system by a number of write periods left in the remaining lifetime of the storage system.

18. The non-transitory computer-readable storage medium of claim 14, wherein the requested data is compressed before being stored in the caching device.

19. The non-transitory computer-readable storage medium of claim 14, wherein the caching device is configured with a log-structured file system, and the requested data is stored at an end of a log of the log-structured file system.

20. The non-transitory computer-readable storage medium of claim 14, wherein the caching device is configured with a log-structured file system, and a compressed version of the requested data is stored at an end of a log of the log-structured file system.