Methods and systems for reducing churn in flash-based cache
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.
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.