Cache auto-flush in a solid state memory device
A device, system and method in which data in a write cache, that must at some point be written to non-volatile memory, is written to non-volatile memory after expiration of a threshold time period during which no new host commands are received. If either the last dirty entry is written back or a host command is received during the write-back process, the time threshold time period and auto-flush process is restarted.
1. A solid state memory device comprising:
a solid state non-volatile memory array;
a cache coupled to the non-volatile memory array; and
a processor arranged to control the writing of data from the cache to the non-volatile memory array and operative to enable actions including:
starting a threshold time period when the cache contains dirty data;
re-starting the threshold time period on receipt of one of a plurality of host commands;
writing the dirty data to the non-volatile memory array on expiration of the threshold time period; and terminating the writing of dirty data to the non-volatile memory array and re-starting the threshold time period when the cache contains dirty data either on receipt of one of the plurality of host commands or after a last set of dirty data from the cache is written to the non-volatile memory.
2. The memory device of claim 1 , wherein the processor is operative to further enable actions including:
determining that the cache contains dirty data; and
determining the threshold time period based on a timer.
3. The memory device of claim 1 , wherein the processor is operative to further enable actions including:
setting the threshold time period so that the writing of the dirty data to the non volatile memory does not exceed a maximum number of write accesses for a predicted life span of the non-volatile memory.
4. The memory device of claim 1 , wherein the processor is further operative to enable actions including:
setting the threshold time period based on the number of dirty entries in the cache or the frequency of host commands.
5. The memory device of claim 1 , wherein writing the dirty data to the non-volatile memory array takes place according to an amount of time that the dirty data has remained in the cache.
6. The memory device of claim 1 , wherein writing the dirty data to the non-volatile memory array includes application of wear-leveling techniques.
7. The memory device of claim 1 , wherein the non-volatile memory array is NAND flash memory.
8. A method for managing caching comprising:
determining that a memory cache contains dirty data;
starting a threshold time period when the memory cache contains dirty data;
re-starting the threshold time period on receiving a host command of a plurality of host commands;
writing the dirty data from the memory cache to a solid state non-volatile memory array on expiration of the threshold time period; and
terminating the writing of dirty data from the memory cache to the solid state non volatile memory array and re-starting the threshold time period when the cache contains dirty data either on receipt of a host command of the plurality of host commands or after a last set of dirty data from the cache is written to the solid state non-volatile memory.
9. The method of claim 8 , wherein the threshold time period is determined based on a timer.
10. The method of claim 8 , wherein the threshold time period is set so that the writing of the dirty data to the non-volatile memory does not exceed a maximum number of write accesses for a predicted life span of the non-volatile memory.
11. The method of claim 8 , further comprising:
setting the threshold time period based on the number of dirty entries in the cache or the frequency of host commands.
12. The method of claim 8 , wherein writing the dirty data to the non-volatile memory array takes place according to an amount of time that the dirty data has remained in the cache.
13. The method of claim 8 , wherein writing the dirty data to the non-volatile memory array includes application of wear-leveling techniques.
14. The method of claim 8 , wherein the non-volatile memory array is NAND flash memory.
15. A solid state drive comprising:
a host interface;
a solid state non-volatile memory array;
a cache coupled to the host interface and the non-volatile memory array; and
a processor for controlling the writing of data from the cache to the non-volatile memory array and operative to enable actions including:
starting a threshold time period when the cache contains dirty data;
re-starting the threshold time period on receipt of one of a plurality of host commands;
writing the dirty data to the non-volatile memory array on expiration of the threshold time period; and
terminating the writing of dirty data to the non-volatile memory array and re-starting the threshold time period either on receipt of one of the plurality of host commands or after a last set of dirty data from the cache is written to the non-volatile memory.
16. The drive of claim 15 , wherein the processor is operative to enable further actions including:
determining the threshold time period based on a timer.
17. The drive of claim 15 , wherein the processor is operative to enable further actions including:
setting the threshold time period so that the writing of the dirty data to the non-volatile memory does not exceed a maximum number of write accesses for a predicted life span of the non-volatile memory.
18. The drive of claim 15 , wherein the processor is further operative to enable actions for:
setting the threshold time period based on the number of dirty entries in the cache or the frequency of host commands.
19. The drive of claim 15 , wherein writing the dirty data to the non-volatile memory array takes place according to an amount of time that the dirty data has remained in the cache.
20. The drive of claim 15 , wherein writing the dirty data to the non-volatile memory array includes application of wear-leveling techniques.