Non-volatile memory and method having block management with hot/cold data sorting

• US 9,176,864 B2
• Filed: 05/10/2012
• Issued: 11/03/2015
• Est. Priority Date: 05/17/2011
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Gorobets, Sergey Anatolievich, Bennett, Alan David, Shippey, Tom Hugh, Parker, Liam Michael, Yaromenka, Yauheni, Sprouse, Steven T., Wu, William S., Bundukin, Marielle
• Primary Examiner(s): Rones, Charles
• Assistant Examiner(s): WONG, NANCI N
• Application Number:
  US13/468,737
• Publication Number:
  US 20120297122A1
• Time in Patent Office: 1,272 Days
• Field of Search: 711/103
• US Class Current: 1/1
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/7202 Allocation control and policies
• CPC Class Codes: G06F 2212/7211 Wear leveling
• CPC Class Codes: G06F 3/0611 in relation to response time
• CPC Class Codes: G06F 3/064 Management of blocks
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G06F 3/068 Hybrid storage device
• CPC Class Codes: G11C 2211/5641 Multilevel memory having cells with different number of storage levels

Abstract

A non-volatile memory organized into flash erasable blocks sorts units of data according to a temperature assigned to each unit of data, where a higher temperature indicates a higher probability that the unit of data will suffer subsequent rewrites due to garbage collection operations. The units of data either come from a host write or from a relocation operation. The data are sorted either for storing into different storage portions, such as SLC and MLC, or into different operating streams, depending on their temperatures. This allows data of similar temperature to be dealt with in a manner appropriate for its temperature in order to minimize rewrites. Examples of a unit of data include a logical group and a block.

Claims

1. A method of operating on units of data in a non-volatile memory, comprising:

organizing the non-volatile memory into blocks of memory cells that are erasable together;

partitioning the non-volatile memory into a SLC portion and an MLC portion, where memory cells in the SLC portion each stores one bit of data and memory cells in the MLC portion each stores more than one bit of data;

providing a plurality of logical groups by partitioning a logical address space of the host into non-overlapping sub-ranges of ordered logical addresses, wherein multiple logical groups are storable in each block and each logical group having a plurality of corresponding logical pages;

providing first and second operational layers in the SLC portion and a third operational layer in the MLC portion;

initially storing host data being written in the first operational layer and subsequently relocating the host data therefrom logical-group by logical-group into either the second or third operational layer;

ranking each logical group by assigning a temperature, the temperature being determined as a function of a time stamp value and potential for future rewrites of each logical group, the time stamp providing a relative measure of how recently written in is each of the logical group, and where a higher temperature indicates a higher probability that the logical group will suffer subsequent rewrites due to garbage collection operations; and

evicting a logical group from the second operational layer to the third operational layer in a manner dependent on the temperature associated with the logical group being evicted.

2. The method as in claim 1, further comprising

providing a predetermined dynamic range of temperature between a lowest temperature and a highest temperature;

and

biasing the temperature in said ranking such that any temperate ranked colder than the lowest temperature is assigned the lowest temperature and any temperature ranked hotter than the highest temperature saturates at the highest temperature.

3. The method as in claim 1, further comprising:

wherein said evicting is in response to a demand to free up room in the SLC portion to preferentially relocating a logical group with the coldest temperature from the second layer of the SLC portion to the third layer of the MLC portion.

4. The method as in claim 1, wherein the temperature associated with a logical group is stored within the logical group.

5. The method as in claim 1, wherein the temperature associated with a logical group is stored in a table in the non-volatile memory.

6. The method as in claim 1, wherein a logical group is ranked a lower temperature when the logical group is less recently written by a host.

7. The method as in claim 1, wherein a logical group is ranked a lower temperature when the logical group is less recently read.

8. The method as in claim 1, wherein a first logical group is ranked a lower temperature than a second logical group when the first logical group is part of a first host write and the first host write is longer than a second host write containing the second logical group.

9. The method as in claim 1, wherein a logical group is ranked to have a lower temperature when the logical group has suffered less number of compaction operations.

10. The method as in claim 1, wherein the logical groups having a size that multiple logical groups fit in a block.

11. The method as in claim 1, wherein:

each unit of data is a block.

12. The method as in claim 11, wherein a block is ranked a lower temperature when the block is less recently written by a host.

13. The method as in claim 1, further including

performing an operation is to store the unit of data with other units of data having similar temperatures within a predetermined range of temperatures.

14. The method as in claim 13, wherein:

the unit of data and the other units of data having similar temperatures are stored in a same block.

15. The method as in claim 14, wherein:

the unit of data is from a host write.

16. The method as in claim 14, wherein:

the unit of data is from a relocation operation.

17. A non-volatile memory for storing units of data, comprising:

a memory array organized into blocks of memory cells that are erasable together;

said memory array being partitioned the non-volatile memory into a SLC portion and an MLC portion, where memory cells in the SLC portion each stores one bit of data and memory cells in the MLC portion each stores more than one bit of data and for storing data logical group by logical group in each block of the SLC portion;

first and second operational layers in the SLC portion and a third operational layer in the MLC portion;

a plurality of logical groups provided by partitioning a logical address space of the host into non-overlapping groups of sequential logical addresses, wherein multiple logical groups are storable in each block and each logical group having a plurality of corresponding logical pages;

the first operational layer for initially storing host data being written and for subsequently relocating therefrom the host data logical-group by logical-group into the second or third layers; and

a state machine controlling operations that include;

ranking each logical group by assigning a temperature, the temperature being determined as a function of a time stamp value and potential for future rewrites of each logical group, the time stamp providing a relative measure of how recently written in is each of the logical group, and where a higher temperature indicates a higher probability that the logical group will suffer subsequent rewrites due to garbage collection operations; and

evicting a logical group from the second operational layer to the third operational layer in a manner dependent on the temperature associated with the logical group being evicted.

18. The non-volatile memory as in claim 17, wherein the operations controlled by the state machine further comprises:

providing a predetermined dynamic range of temperature between a lowest temperature and a highest temperature; and

biasing the temperature in said ranking such that any temperate ranked colder than the lowest temperature is assigned the lowest temperature and any temperature ranked hotter than the highest temperature saturates at the highest temperature.

19. The non-volatile memory as in claim 17, wherein:

said evicting is in response to a demand to free up room in the SLC portion to preferentially relocating a logical group with the coldest temperature from the second layer of the SLC portion to the third layer of the MLC portion.

20. The non-volatile memory as in claim 17, wherein the temperature associated with a logical group is stored within the logical group.

21. The non-volatile memory as in claim 17, wherein the temperature associated with a logical group is stored in a table in the non-volatile memory.

22. The non-volatile memory as in claim 17, wherein a logical group is ranked a lower temperature when the logical group is less recently written by a host.

23. The non-volatile memory as in claim 17, wherein a logical group is ranked a lower temperature when the logical group is less recently read.

24. The non-volatile memory as in claim 17, wherein a first logical group is ranked a lower temperature than a second logical group when the first logical group is part of a first host write and the first host write is longer than a second host write containing the second logical group.

25. The non-volatile memory as in claim 17, wherein a logical group is ranked to have a lower temperature when the logical group has suffered less number of compaction operations.

26. The non-volatile memory as in claim 17, wherein the logical groups having a size that multiple logical groups fit in a block.

27. The non-volatile memory as in claim 17, wherein:

each unit of data is a block.

28. The non-volatile memory as in claim 27, wherein a block is ranked a lower temperature when the block is less recently written by a host.

29. The non-volatile memory as in claim 17, wherein:

said performing an operation is to store the unit of data with other units of data having similar temperatures within a predetermined range of temperatures.

30. The non-volatile memory as in claim 29, wherein:

the unit of data and the other units of data having similar temperatures are stored in a same block.

31. The non-volatile memory as in claim 30, wherein:

the unit of data is from a host write.

32. The non-volatile memory as in claim 30, wherein:

the unit of data is from a relocation operation.