Persistent Storage Device with NVRAM for Staging Writes

• US 20140181373A1
• Filed: 03/14/2013
• Published: 06/26/2014
• Est. Priority Date: 12/26/2012
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Enterprise IP LLC (Western Digital Corporation)
• Inventors: George, Johann, Olbrich, Aaron, O'Krafka, Brian, Dinker, Darpan, Chiu, Patrick, Firsov, Evgeny
• Granted Patent: US 9,501,398 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 2212/7203 Temporary buffering, e.g. using volatile buffer or dedicated buffer blocks
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/0656 Data buffering arrangements
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]

Abstract

A persistent storage device includes both persistent storage, which includes a set of persistent storage blocks, and NVRAM, and in particular a set of NVRAM blocks. The persistent storage device also typically includes a storage controller. The persistent storage device, in addition to responding to commands to write data directly to and to read data directly from persistent storage blocks is also configured to write data to specified NVRAM blocks (e.g., specified by a host NVRAM write command) and to transfer data from a specified NVRAM block to a specified persistent storage block. As a result, multiple writes to a particular persistent storage block can be replaced with multiple writes to an NVRAM block and a subsequent single write to the particular persistent storage block. This reduces the number of writes to persistent storage and also reduces the number of corresponding block erase operations.

Claims

1. A persistent storage device, comprising:

persistent storage, comprising a set of persistent storage blocks;

NVRAM, comprising a type of nonvolatile storage distinct from the persistent storage and comprising a set of NVRAM blocks;

a storage controller configured to receive commands from an external host device and further configured to;

in response to a transfer command, transfer data in a specified NVRAM block to a corresponding persistent storage block, wherein the data was previously written to the specified NVRAM block.

2. The persistent storage device of claim 1, wherein the storage controller is further configured to:

in response to a host NVRAM write command, store data to a specified NVRAM block;

in response to a host persistent storage write command, store data to a specified persistent storage block; and

in response to a host persistent storage read command, retrieve data from the specified persistent storage block.

3. The persistent storage device of claim 2, wherein the persistent storage device is implemented as a single, monolithic integrated circuit.

4. The persistent storage device of claim 2, wherein the persistent storage comprises flash memory, and the NVRAM comprises non-volatile storage selected from the set consisting of EPROM, EEPROM, battery backed SRAM, battery backed DRAM, supercapacitor backed DRAM, ferroelectric RAM, magnetoresistive RAM, and phase-change RAM.

5. The persistent storage device of claim 2, further comprising a host interface for interfacing the persistent storage device to a memory controller of the external host device.

6. The persistent storage device of claim 2, wherein the storage controller is further configured to respond to a host NVRAM read command by retrieving data from the specified NVRAM block.

7. The persistent storage device of claim 2, wherein a logical block address is associated with the specified NVRAM block, and the corresponding persistent storage block corresponds to the logical block address.

8. The persistent storage device of claim 2, wherein the storage controller is further configured to respond to a respective host command by storing a logical block address, specified by the host command, in association with the specified NVRAM block.

9. The persistent storage device of claim 2, wherein a predefined portion of the NVRAM stores one or more logical block addresses, each associated with a respective NVRAM block.

10. The persistent storage device of claim 2, wherein a logical block address is associated with the specified NVRAM block, and the corresponding persistent storage block is identified by the storage controller using a logical block address to physical address mapping.

11. The persistent storage device of claim 2, wherein

the transfer command comprises a first predefined transfer command, and

the storage controller is further configured to respond to a second predefined transfer command by storing data in a persistent storage block specified by the second predefined transfer command to a NVRAM block specified by the second predefined transfer command.

12. A method for managing a persistent storage device, comprising:

at the persistent storage device comprising persistent storage and NVRAM, the persistent storage comprising a set of persistent storage blocks and the NVRAM, comprising a type of nonvolatile storage distinct from the persistent storage and comprising a set of NVRAM blocks;

receiving commands from an external host device;

in response to a transfer command, storing data in a NVRAM block specified by the transfer command to a corresponding persistent storage block.

13. The method of claim 12, further comprising:

in response to a host NVRAM write command, storing data to a specified NVRAM block;

in response to a host persistent storage write command, storing data to a specified persistent storage block; and

in response to a host persistent storage read command, retrieving data from the specified persistent storage block.

14. The method of claim 13, wherein the persistent storage device is implemented as a single, monolithic integrated circuit.

15. The method of claim 13, wherein the persistent storage comprises flash memory, and the NVRAM comprises non-volatile storage selected from the set consisting of EPROM, EEPROM, battery backed SRAM, battery backed DRAM, supercapacitor backed DRAM, ferroelectric RAM, magnetoresistive RAM, and phase-change RAM.

16. The method of claim 13, wherein the persistent storage device further comprises a host interface for interfacing the persistent storage device to a memory controller of the external host device.

17. The method of claim 13, further comprising, at the persistent storage device, responding to a host NVRAM read command by retrieving data from the specified NVRAM block.

18. The method of claim 13, wherein a logical block address is associated with the specified NVRAM block, and the corresponding persistent storage block corresponds to the logical block address.

19. The method of claim 13, further comprising, at the persistent storage device, responding to a respective host command by storing a logical block address, specified by the host command, in association with the specified NVRAM block.

20. The method of claim 13, further comprising, at the persistent storage device, storing one or more logical block addresses in the NVRAM, each associated with a respective NVRAM block.

21. The method of claim 13, further comprising, at the persistent storage device, identifying, for the transfer command, the corresponding persistent storage block using a logical block address to physical address mapping.

22. The method of claim 13, wherein the transfer command comprises a first predefined transfer command, the method further comprising, at the persistent storage device, in response to a second predefined transfer command, storing data in a persistent storage block specified by the second predefined transfer command to a NVRAM block specified by the second predefined transfer command.

23. The method of claim 13, further comprising, at the persistent storage device, automatically transferring data from NVRAM to persistent storage upon occurrence of a predefined trigger condition selected from the set consisting of the amount of data stored to the specified NVRAM block reaching a predefined threshold and data being stored to a predefined portion of the specified NVRAM block.

24. The method of claim 13, further comprising, under control of the external host device:

after loss of power, reading from NVRAM a set of logical block addresses, including the logical block address, if any, associated with each NVRAM block in the set of NVRAM blocks; and

copying data from each NVRAM block having an associated logical block address to a persistent storage block corresponding to the associated logical block address.

25. A method for storing data to a persistent storage device, comprising:

at a host device external to the persistent storage device;

issuing a plurality of NVRAM write commands to store data in a specified block of NVRAM in the persistent storage device, the persistent storage device comprising persistent storage and NVRAM, the persistent storage comprising a set of persistent storage blocks and the NVRAM comprising a set of NVRAM blocks that includes the specified block of NVRAM, wherein the NVRAM comprises a type of nonvolatile storage distinct from the persistent storage;

issuing a predefined transfer command, instructing the persistent storage device to store data in the specified NVRAM block to a corresponding persistent storage block; and

issuing a read command, instructing the persistent storage device to retrieve data from the persistent storage block corresponding the specified NVRAM block, and to convey to the host device the data retrieved from the persistent storage block corresponding the specified NVRAM block.