Storage system using flash memory

• US 20060288153A1
• Filed: 09/19/2005
• Published: 12/21/2006
• Est. Priority Date: 06/21/2005
• Status: Active Grant

• Current Assignee: Rakuten Group, Inc.
• Original Assignee: Hitachi, Ltd.
• Inventors: Tanaka, Katsuya, Ishida, Manabu
• Granted Patent: US 7,613,871 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 12/1425 the protection being physical, e.g. cell, word, block
• CPC Class Codes: G06F 2212/2022 Flash memory
• CPC Class Codes: G11C 16/22 Safety or protection circuits preventing unauthorised or accidental access to memory cells
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles

Abstract

Provided is a storage system including: a nonvolatile memory which stores and erases data for respective blocks; and a controller for inputting and outputting the data to and from the nonvolatile memory, wherein: the storage system has a storage area including: a rewritable area where a stored data can be erased; and a write-once area where the stored data cannot be erased; and the controller determines a block belonging to the rewritable area based on an attribute of the block, and performs a wear leveling process and a reclamation process only on the block determined as belonging to the rewritable area.

Claims

1. A storage system, comprising:

a nonvolatile memory which erases data for respective blocks; and

a controller for inputting and outputting the data to and from the nonvolatile memory, wherein;

the storage system has a storage area including;

a rewritable area where a stored data can be erased; and

a write-once area where the stored data cannot be erased; and

the controller determines a block belonging to the rewritable area based on an attribute of the block, and performs a wear leveling process and a reclamation process only on the block determined as belonging to the rewritable area.

2. The storage system according to claim 1, wherein the attribute of the block indicates which of the rewritable area and the write-once area the block belongs to.

3. The storage system according to claim 1, wherein each of the blocks stores the attribute of the block in a predetermined area of the block.

4. The storage system according to claim 1, wherein:

the block comprises a plurality of pages each being a write unit of the data;

the write-once area is one of a first write-once area including one or more pages to which no data is written and a second write-once area in that the data is written to all of the pages; and

the attribute of the block indicates which of the rewritable area, the first write-once area, and the second write-once area the block belongs to.

5. The storage system according to claim 4, wherein the controller reports an error without writing data when receiving a write request of the data to the block belonging to the second write-once area.

6. The storage system according to claim 4, wherein:

when receiving the write request of data to the block belonging to the first write-once area, the controller determines whether or not data is written to the page based on the attribute of the page to which the data is to be written;

when data is not written to the page, the controller writes the data to the page and changes the attribute of the block including the page from the attribute indicating the first write-once area to the attribute indicating the second write-once area; and

when the data is written to the page, the controller reports an error without writing the data.

7. The storage system according to claim 1, wherein the controller changes the rewritable area to the write-once area by changing the attribute of the block on which the reclamation process is performed.

8. The storage system according to claim 7, wherein:

the block stores the number of times of erasing of the data in the block; and

the controller gives a priority to the block where the number of times of erasing is large to change the rewritable area to the write-once area by changing the attribute of the block on which the reclamation process is performed.

9. The storage system according to claim 1, wherein the controller writes the data to the block when receiving the write request of the data to the block belonging to the rewritable area, and changes the rewritable area to the write-once area by changing the attribute of the block.

10. The storage system according to claim 1, wherein the block stores a retention period information of the stored data.

11. The storage system according to claim 10, wherein the controller writes the data to the block and writes the retention period information of the data to the block when receiving the write request of the data.

12. The storage system according to claim 10, wherein:

the storage system has a storage area including;

the rewritable area where the stored data can be erased;

the write-once area where the stored data cannot be erased; and

an unused area for which the attribute is not determined; and

the controller erases data whose retention period expires from the block that stores the data, and changes the write-once area to the unused area by changing the attribute of the block.