SYSTEM AND METHOD TO BUFFER DATA

• US 20120317365A1
• Filed: 06/07/2011
• Published: 12/13/2012
• Est. Priority Date: 06/07/2011
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: ELHAMIAS, REUVEN
• Granted Patent: US 10,031,850 B2
• Time in Patent Office: Days
• US Class Current: 711/141
• CPC Class Codes: G06F 12/0862 with prefetch
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 2212/214 Solid state disk
• CPC Class Codes: G06F 2212/221 Static RAM
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A data storage device includes a controller, a non-volatile memory, and a buffer accessible to the controller. The buffer is configured to store data retrieved from the non-volatile memory to be accessible to a host device in response to receiving from the host device one or more requests for read access to the non-volatile memory while the data storage device is operatively coupled to the host device. The controller is configured to read an indicator of cached data in response to receiving a request for read access to the non-volatile memory. The request includes a data identifier. In response to the indicator of cached data not indicating that data corresponding to the data identifier is in the buffer, the controller is configured to retrieve data corresponding to the data identifier as well as additional data from the non-volatile memory and to write the data corresponding to the data identifier and the additional data to the buffer. The controller is configured to update the indicator of cached data in response to retrieved data from the non-volatile memory being written to the buffer.

Claims

1. A method comprising:

in a data storage device with a controller, a non-volatile memory, and a buffer, performing;

receiving a request for read access, the request including a data identifier, wherein the request for read access is received from a host device while the data storage device is operatively coupled to the host device;

reading an indicator of cached data to determine whether the data identifier in the read access request corresponds to data which is cached in the buffer;

in response to determining that, based on the data identifier and the indicator of cached data, no data corresponding to the data identifier is cached in the buffer;

retrieving from the non-volatile memory data corresponding to the data identifier in the read access request as well as additional data;

caching the data and the additional data in the buffer; and

updating the indicator of cached data with both the data identifier and another data identifier corresponding to the additional data; and

providing the data corresponding to the data identifier from the buffer to the host device,

wherein caching the additional data to the buffer enables the data storage device to bypass retrieving the additional data from the non-volatile memory in response to a subsequent request for read access to the additional data.

2. The method of claim 1, wherein the additional data is subsequent data that is retrieved in accordance with a read-ahead operation in anticipation of receiving the subsequent request for read access with the other data identifier.

3. The method of claim 1, wherein the additional data is stored in a same data read unit of the non-volatile memory as the data.

4. The method of claim 1, wherein the data identifier and the other data identifier are sequential logical block addresses.

5. The method of claim 1, wherein the data identifier and the other data identifier are sequential physical addresses.

6. The method of claim 1, wherein the data identifier and the other data identifier identify a file and correspond to sequential portions of the file.

7. The method of claim 1, wherein the data and the additional data are retrieved from the non-volatile memory as portions of a single codeword that is read from the non-volatile memory.

8. The method of claim 1, wherein the indicator of cached data includes a list of one or more entries, each entry including an identifier of corresponding data stored in the buffer.

9. The method of claim 8, wherein the data identifier includes a first address, wherein the identifier in each particular entry of the list indicates a starting address and length information of the corresponding data in the buffer, and wherein reading the indicator to determine whether the data identifier in the read access request corresponds to data which is cached in the buffer includes:

reading the starting address and the length information from a first entry of the list to determine whether the corresponding data for the first entry includes the data corresponding to the data identifier; and

in response to determining that the corresponding data for the first entry does not include the data corresponding to the data identifier, reading the starting address and the length information from a second entry of the list.

10. The method of claim 8, further comprising, in response to receiving a request for write access that includes the data identifier, modifying the list to prevent the data corresponding to the data identifier at the buffer from being read from the buffer.

11. The method of claim 10, further comprising, in response to receiving the request for write access including the data identifier, modifying the list to prevent all data that has been written to the buffer in response to read requests from being read from the buffer.

12. The method of claim 10, wherein modifying the list includes locating an entry corresponding to the data identifier and performing at least one of modifying a starting address in the located entry, modifying length information in the located entry, and modifying a buffer address in the located entry.

13. The method of claim 1, wherein the non-volatile memory includes a flash memory and wherein the buffer is a random access memory (RAM) that is accessible to the controller.

14. A data storage device comprising:

a controller;

a non-volatile memory; and

a buffer accessible to the controller, wherein the buffer is configured to store data retrieved from the non-volatile memory, the data to be accessible to a host device in response to receiving from the host device one or more requests for read access to the non-volatile memory while the data storage device is operatively coupled to the host device,

wherein the controller is configured to read an indicator of cached data in response to receiving a request for read access to the non-volatile memory, the request including a data identifier, and in response to the indicator of cached data not indicating that data corresponding to the data identifier is in the buffer, to retrieve the data corresponding to the data identifier as well as additional data from the non-volatile memory and to write the data corresponding to the data identifier and the additional data to the buffer, and

wherein the controller is configured to update the indicator of cached data to indicate the data identifier and another data identifier corresponding to the additional data in response to the data corresponding to the data identifier and the additional data from the non-volatile memory being written to the buffer.

15. The data storage device of claim 14, wherein the controller is configured to read the data corresponding to the data identifier and the additional data from the non-volatile memory in a pipelined manner, wherein during a first time period the data corresponding to the data identifier is retrieved from the non-volatile memory and written to the buffer and wherein during a subsequent time period the data corresponding to the data identifier is provided from the buffer to the host device while the additional data is retrieved from the non-volatile memory and written to the buffer.

16. The data storage device of claim 15, wherein the data identifier and the other data identifier corresponding to the additional data are sequential logical block addresses (LBAs) and wherein the controller is configured to load retrieved data from the non-volatile memory to the buffer in the pipelined manner according to a sequence of LBAs until a command to stop reading is received from the host device.

17. The data storage device of claim 14, wherein the controller is configured to read the data corresponding to the data identifier and the additional data from the non-volatile memory as portions of a single codeword that is stored at the non-volatile memory, the single codeword including a data portion and a parity portion, and wherein the controller is configured to write the data corresponding to the data identifier and the additional data from the data portion of the single codeword to the buffer in response to receiving the request for read access.

18. The data storage device of claim 14, wherein the data identifier and the other data identifier are sequential logical block addresses.

19. The data storage device of claim 14, wherein the data identifier and the other data identifier are sequential physical addresses.

20. The data storage device of claim 14, wherein the data identifier and the other data identifier identify a file and correspond to sequential portions of the file.

21. The data storage device of claim 14, wherein the indicator of cached data includes a list of one or more entries, each entry including an identifier of corresponding data in the buffer.

22. The data storage device of claim 21, wherein each particular entry of the list indicates a starting address and length information of the data in the buffer corresponding to the particular entry, and wherein the controller is configured to read the indicator to determine whether the data corresponding to the data identifier is in the buffer by:

reading the starting address and the length information from a first entry of the list to determine whether the corresponding data for the first entry includes the data corresponding to the data identifier; and

in response to determining that the corresponding data for the first entry does not include the data corresponding to the data identifier, reading the starting address and the length information from a second entry of the list.

23. The data storage device of claim 21, wherein the controller is configured to modify the list to prevent data at the buffer from being read from the buffer in response to receiving a request for write access to the non-volatile memory.

24. The data storage device of claim 23, wherein the controller is configured to locate an entry corresponding to the data corresponding to the data identifier and to perform at least one of modifying a starting address in the located entry, modifying length information in the located entry, and modifying a buffer address in the located entry.

25. The data storage device of claim 14, wherein the non-volatile memory includes a flash memory and wherein the buffer is a random access memory (RAM) that is accessible to the controller.