METHODS AND SYSTEMS FOR REDUCING CHURN IN FLASH-BASED CACHE

• US 20140244918A1
• Filed: 05/08/2014
• Published: 08/28/2014
• 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
• Granted Patent: US 9,003,113 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• 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 of throttling cache updates in a storage device having a flash memory-based cache and a disk-based storage unit, the method comprising:

a controller determining a threshold number of permitted writes per write period, by dividing a remaining number of writes that can be tolerated by the storage device into a remaining number of write periods remaining in an expected service lifetime for the storage device, wherein the write periods comprise periods of fixed interval and the threshold number of permitted writes per write period is updated periodically; and

for a subject write period, the controller monitoring the number of writes to the cache during the subject write period and allowing, at most, that number of writes equal to the threshold number of permitted writes for the subject write period.

2. The method of claim 1, further comprising the controller throttling updates to the cache according to user instructions concerning a data type of the data.

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

4. The method of claim 1, further comprising the controller determining whether the data comprises sequentially-accessed data, and, if so, to writing the data only to the disk-based storage unit.

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

6. The method of claim 1, wherein the received data comprises compressed data further, the method further comprising throttling updates to the cache by permitting only a threshold number of writes per write period to the cache, wherein each write period comprises a period of fixed interval.

7. The method of claim 1, wherein the received data comprises compressed data and the updates to the cache are throttled in accordance with user input concerning whether or not the data is to be cached.

8. The method of claim 1, wherein the received data comprises compressed data and if the data comprises sequentially-accessed data, the data is written only to the disk-based storage unit.

9. The method of claim 1, wherein the received data comprises compressed data and if the data comprises sequentially-accessed data, the data is written only to the disk-based storage unit and updates to the cache are throttled in accordance with user input concerning whether or not the data is to be cached.

10. The method of claim 1, wherein the received data comprises compressed data and if the data comprises sequentially-accessed data, the data is written only to the disk-based storage unit and updates to the cache are made by permitting only a threshold number of writes per write period to the cache, wherein each write period comprises a period of fixed interval.

11. The method of claim 1, wherein the received data comprises compressed data and if the data comprises sequentially-accessed data, the data is written only to the disk-based storage unit, updates to the cache are made by permitting only a threshold number of writes per write period to the cache, wherein each write period comprises a period of fixed interval, and updates to the cache are throttled in accordance with user input concerning whether or not the data is to be cached.

12. 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 throttle updates to the cache by determining a threshold number of permitted writes per write period by dividing a remaining number of writes that can be tolerated by the storage device into a remaining number of write periods remaining in an expected service lifetime for the storage device, wherein the write periods comprise periods of fixed interval and the threshold number of permitted writes per write period is updated periodically;

for a subject write period, monitoring the number of writes to the cache during the subject write period; and

allowing, at most, that number of writes equal to the threshold number of permitted writes for the subject write period.

13. The storage device of claim 12, wherein the controller is further configured to throttle updates to the cache according to user instructions concerning a data type of the data.

14. The storage device of claim 12, wherein the controller is further configured to determine whether the data comprises sequentially-accessed data, and, if so, to write the data only to the disk-based storage unit.

15. The storage device of claim 12, wherein the controller is further configured to compress data to be stored to the cache prior to writing compressed data to the cache.

16. The storage device of claim 12, wherein the controller is further configured to throttle updates to the cache by permitting only a threshold number of writes per write period to the cache, wherein each write period comprises a period of fixed interval.

17. The storage device of claim 12, wherein the controller is further configured to throttle updates to the cache in accordance with user input concerning whether or not the data is to be cached.

18. The storage device of claim 12, wherein the received data comprises compressed data.

19. A tangible computer-readable media including a set of instructions stored thereon for throttling cache updates in a storage device having a flash memory-based cache and a disk-based storage unit, wherein execution of the set of instructions by a controller cause the controller to:

determine a threshold number of permitted writes per write period by dividing a remaining number of writes that can be tolerated by the storage device into a remaining number of write periods remaining in an expected service lifetime for the storage device, wherein the write periods comprise periods of fixed interval and the threshold number of permitted writes per write period is updated periodically; and

for a subject write period, monitor the number of writes to the cache during the subject write period and allow, at most, that number of writes equal to the threshold number of permitted writes for the subject write period.