DISK DRIVE DATA CACHING USING A MULTI-TIERED MEMORY

• US 20130132638A1
• Filed: 11/21/2011
• Published: 05/23/2013
• Est. Priority Date: 11/21/2011
• Status: Active Grant

• Current Assignee: JP Morgan Chase Bank, N.A. (JP Morgan Chase & Co)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Horn, Robert L., Booth, Jing, Guda, Chandra M.
• Granted Patent: US 8,977,803 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G06F 12/0871 Allocation or management of cache space
• CPC Class Codes: G06F 12/0897 with two or more cache hierarchy levels with multilevel cache hierarchies G06F12/0811
• CPC Class Codes: G06F 2212/217 Hybrid disk, e.g. using both magnetic and solid state storage devices
• CPC Class Codes: G06F 2212/222 Non-volatile memory
• CPC Class Codes: G06F 2212/6042 Allocation of cache space to multiple users or processors
• CPC Class Codes: G11C 2211/5641 Multilevel memory having cells with different number of storage levels
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A disk drive is disclosed that utilizes multi-tiered solid state memory for caching data received from a host. Data can be stored in a memory tier that can provide the required performance at a low cost. For example, multi-level cell (MLC) memory can be used to store data that is frequently read but infrequently written. As another example, single-level cell (SLC) memory can be used to store data that is frequently written. Improved performance, reduced costs, and improved power consumption can thereby be attained.

Claims

1. In a disk drive system comprising a magnetic medium and a multi-level cell (MLC) non-volatile memory module comprising a single-level cell (SLC) memory tier and an MLC memory tier, a method of caching data in the non-volatile memory, the method comprising:

maintaining first and second candidate lists of data values corresponding to addresses in the magnetic medium to be considered for caching, the maintaining comprising;

in response to receiving a storage access command from a host, the storage access command comprising an address in the magnetic medium configured to store a data value, determining a metric corresponding to a frequency of access by the host; and

determining a placement of the data value in one of the first and second candidate lists based on a comparison of the metric to a threshold; and

selectively programming entries in the first and second candidate lists in the SLC memory tier or the MLC memory tier.

2. The method of claim 1, wherein determining the metric comprises combining at least two of the following:

write frequency, write performance, read frequency, read performance, and retention duration.

3. The method of claim 2, wherein the combining further comprises computing an average.

4. The method of claim 3, wherein the average is a weighted average.

5. The method of claim 2, wherein determining the placement of the data value comprises:

comparing the metric to a first threshold, and if the metric exceeds the first threshold, determining the placement of the data value in the first candidate list; and

if the metric does not exceed the first threshold, comparing the metric to a second threshold, and if the metric exceeds the second threshold, determining the placement of the data value in the second candidate list.

6. The method of claim 5, wherein entries in the first candidate list are ordered according to their metrics and entries in the second candidate list are ordered according to their metrics.

7. The method of claim 6, wherein the programming further comprises replacing a lowest priority entry in the SLC memory tier with a highest priority data value in the first candidate list provided that a metric of the highest priority entry in the first candidate list exceeds a metric of the lowest priority data value in the SLC memory tier.

8. The method of claim 6, wherein the programming further comprises replacing a lowest priority entry in the MLC memory tier with a highest priority entry in the second candidate list provided that a metric of the highest priority entry in the second candidate list exceeds a metric of the lowest priority entry in the MLC memory tier.

9. The method of claim 1, wherein determining the metric comprises combining at least a read frequency and a write frequency.

10. The method of claim 9, wherein the read frequency corresponds to tracking a frequency of read commands comprising the address and the write frequency corresponds to tracking a frequency of write commands comprising the address.

11. The method of claim 10, wherein tracking the frequency of read commands comprises incrementing a first counter and the tracking the frequency of write commands comprises incrementing a second counter.

12. A disk drive system for storing data received from a host, the system comprising:

a magnetic medium configured to store data;

a non-volatile memory capable of supporting both a multi-level cell (MLC) memory tier and a single-level cell (SLC) memory tier; and

a controller configured to access at least the non-volatile memory in response to receiving a storage access command from the host, the storage access command comprising an address in the magnetic medium configured to store a data value, the controller further configured to;

determine a metric corresponding to a frequency of access by the host;

determine a placement of the data value in one of first and second candidate lists based on a comparison of the metric to a threshold; and

selectively program entries in the first and second candidate lists into the SLC memory tier or the MLC memory tier.

13. The system of claim 12, wherein the controller is further configured to determine the metric by combining at least two of the following:

write frequency, write performance, read frequency, read performance, and retention duration.

14. The system of claim 13, wherein the read frequency corresponds to tracking a frequency of read commands comprising the address and the write frequency corresponds to tracking a frequency of write commands comprising the address.

15. The system of claim 13, wherein the controller is further configured to:

compare the metric to a first threshold, and if the metric exceeds the first threshold, determine the placement of the data value in the first candidate list; and

if the metric does not exceed the first threshold, compare the metric to a second threshold, and if the metric exceeds the second threshold, determine the placement of the data value in the second candidate list.

16. The system of claim 15, wherein the controller is further configured to order entries in the first candidate list according to their metrics and to order entries in the second candidate list according to their metrics.

17. The system of claim 16, wherein the controller is further configured to program a highest priority entry in the first candidate list in the SLC memory tier provided that a metric of the highest priority entry in the first candidate list exceeds a metric of a lowest priority entry in the SLC memory tier.

18. The system of claim 17, wherein the highest priority entry comprises data used by the host during initialization.

19. The system of claim 18, wherein the controller is further configured to program a highest priority entry in the second candidate list into the MLC memory tier provided that a metric of the highest priority entry in the second candidate list exceeds a metric of a lowest priority entry in the MLC memory tier.

20. The system of claim 12, wherein the non-volatile memory comprises MLC memory.

21. The system of claim 12, wherein the controller is further configured to increment a first counter in response to receiving a read command comprising the address and increment a second counter in response to receiving a write command comprising the address.

22. The system of claim 21, wherein the controller is further configured to combine by computing an average.

23. The system of claim 22, wherein the average is a weighted average.

24. In a disk drive system comprising a magnetic medium and non-volatile memory that comprises at least first and second tiers of storage, a method of caching data in the non-volatile memory, the method comprising:

maintaining first and second candidate lists of entries corresponding to logical address ranges in the magnetic medium to be considered for caching, the maintaining comprising;

identifying a plurality of logical address ranges that are frequently accessed by a host, each logical address range in the plurality of logical address ranges corresponding to one or more locations in the magnetic medium;

for each logical address range in the plurality of logical address ranges that are frequently accessed by the host;

determining a metric corresponding to a combination of at least two of the following;

write frequency, write performance, read frequency, read performance, and retention duration;

determining a placement of an entry corresponding to the logical address range in one of the first and second candidate lists based on a comparison of the metric to one or more thresholds,

wherein entries in the first and second candidate lists are ordered according to their metrics; and

programming entries in the first and second candidate lists in the non-volatile memory, the programming comprising;

replacing a lowest priority entry in the first tier storage with a highest priority entry in the first candidate list when a metric of the highest priority entry in the first candidate list exceeds a metric of the lowest priority entry in the first tier storage; and

replacing a lowest priority entry in the second tier storage with a highest priority entry in the second candidate list when a metric of the highest-priority entry in the second candidate list exceeds a metric of the lowest priority entry in the second tier storage.

25. The method of claim 24, wherein the entry comprises a data value intended to be stored in a location corresponding to the logical address range.

26. The method of claim 24, wherein identifying the plurality of logical address ranges that are frequently accessed by the host comprises identifying logical address ranges that are frequently accessed during an initialization of the host or during a normal operation of the host.

27. The method of claim 24, wherein the non-volatile memory comprises solid-state memory.

28. The method of claim 24, wherein the non-volatile memory comprises at least another additional tier of storage.

29. A method of caching data in solid state memory of a disk drive, the method comprising:

receiving a unit of data from a host system;

calculating at least one metric that represents a prediction of how the unit of data will be accessed by the host system, said metric being dependent upon at least (1) a write address used by the host system to write the unit of data to the disk drive, and (2) statistical data reflective of prior accesses by the host system to the disk drive; and

selecting, based at least partly on the metric, a memory tier in which to cache the unit of data, wherein selecting the memory tier comprises selecting between at least a first tier composed of single-level cell (SLC) memory and a second tier composed of multi-level cell (MLC) memory.