Semiconductor storage device and data control method thereof

• US 9,063,663 B2
• Filed: 09/21/2010
• Issued: 06/23/2015
• Est. Priority Date: 09/21/2010
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Suzuki, Akifumi, Kawamura, Atsushi, Ogawa, Junji
• Primary Examiner(s): THAI, TUAN V
• Application Number:
  US12/936,176
• Publication Number:
  US 20120072641A1
• Time in Patent Office: 1,736 Days
• Field of Search: 711/100, 711/103, 711/154
• US Class Current: 1/1
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/1036 Life time enhancement
• CPC Class Codes: G06F 2212/401 Compressed data
• CPC Class Codes: G06F 2212/7201 Logical to physical mapping or translation of blocks or pages
• CPC Class Codes: G06F 2212/7203 Temporary buffering, e.g. using volatile buffer or dedicated buffer blocks
• CPC Class Codes: G06F 2212/7205 Cleaning, compaction, garbage collection, erase control
• CPC Class Codes: G06F 2212/7208 Multiple device management, e.g. distributing data over multiple flash devices
• CPC Class Codes: G06F 3/0608 Saving storage space on storage systems
• CPC Class Codes: G06F 3/064 Management of blocks
• CPC Class Codes: G06F 3/0688 Non-volatile semiconductor memory arrays

Abstract

The flash memory controller compresses data in response to a write request. On condition that there is a compression effect with respect to the compressed data, the flash memory controller writes the compressed data to the base area of a physical block of a flash memory. As physical pages assigned to the physical block, the flash memory controller reduces the physical pages assigned to the base area from 102 down to 59, and increases the physical pages assigned to the update area from 26 up to 69. Therefore, it is possible to suppress exhaustion of physical pages which are assigned to the update area, to reduce the number of erases of the physical block, and to consequently prolong device operating life.

Claims

1. A semiconductor storage device, comprising:

a plurality of flash memory chips, comprising a plurality of physical blocks, each of which is a unit of erasing data, and comprises a plurality of physical pages, each of which is a unit of reading or writing data; and

a flash memory controller configured to control a reading or writing operation to the plurality of flash memory chips,

wherein the flash memory controller is configured to;

receive write data;

compress the write data to compressed data;

store the compressed data into at least one physical page of the plurality of flash memory chips when a number of physical pages required to store the compressed data is smaller than a number of physical pages required to store the write data;

manage a logical address space which is an access target of an access request source by dividing the logical address space into a plurality of logical pages, and manage each of the pages in association with the physical pages which belong to an of the physical blocks, and when any of the logical pages is designated in response to a write request from the access request source;

select one, two or more of the physical pages as physical pages which correspond to the designated logical pages; and

store compressed write data on the selected physical pages, form a virtual physical page for storing the compressed write data as data when the compressed write data is virtually decompressed, and change the corresponding relationship between the designated logical page and the one, two or more of the physical pages of the physical block corresponding to the logical page into a corresponding relationship between the designated logical page and the virtual physical pages;

when a logical page, which is the same as the designated logical page, is designated in response to a subsequent access request, process the virtual physical page as an access destination;

accumulate write data which is added to each of the write requests each time a write request is received from the access request source, and batch-compress a plurality of the accumulated write data;

when a compression effect of the compressed write data is greater than a designated value, assuming said condition is fulfilled, store the compressed write data on the selected physical page; and

when the compression effect of the compressed write data is smaller than a designated value, assuming said condition is fulfilled, store the write data added to each of the write requests on the selected physical page.

2. The semiconductor storage device according to claim 1,

wherein each of the physical blocks is divided into a base area configured to store new write data among the write data related to a write request and into an update area configured to store an update data which is configured to update the data stored in the base area, and a plurality of physical pages are respectively assigned to the base area and the update area,

wherein the flash memory controller is configured to:

manage a logical address space which is an access target;

divide the logical address space into a plurality of logical groups, wherein each of the logical groups is associated with the base area of each of the physical blocks;

receive a write request designating a logical address of the logical address space;

specify a logical group including the designated logical address;

select a physical block within the base area for storing the compressed write data;

store the compressed write data into a physical page in the selected physical block;

form a virtual page assigned to the physical page which stores the compressed data, for managing the compressed write data as data when the compressed write data is virtually decompressed;

change the corresponding relationship between the specified logical group and the physical page into a corresponding relationship between the specified logical group and the virtual page; and

process the physical page which is assigned to the virtual page as an access destination when the specified logical group, is designated by a subsequent access request.

3. The semiconductor storage device according to claim 1,

wherein each of the physical blocks is divided into a base area which is a storage destination of new write data among write data applied to the access request and an update area which is a storage destination of update data, and a plurality of physical pages are respectively assigned to the base area and the update area,

wherein when, as a result of the write data compression, the physical pages serving as write targets among the physical pages which belong to the selected physical block are reduced, the flash memory controller is configured to:

reduce a number of physical pages assigned to the base area belonging to the selected physical block; and

increase a number of physical pages assigned to the update area belonging to the selected physical block.

4. The semiconductor storage device according to claim 1,

wherein each of the physical blocks is divided into a base area which is a storage destination of new write data among write data applied to the access request and an update area which is a storage destination of update data, and a plurality of physical pages are respectively assigned to the base area and the update area,

wherein the flash memory controller is configured to:

compare, among the write data, the data size of the write data before the compression with the data size of the write data after the compression;

write the write data after the compression to the base area when the data size of the write data after the compression is smaller than the data size of the write data before the compression by at least size of the physical page; and

write the write data before the compression to the base area when the data size of the write data after the compression is not smaller than the data size of the write data before the compression by at least size of the physical page.

5. The semiconductor storage device according to claim 1,

wherein each of the physical blocks is divided into a base area which is a storage destination of new write data among write data applied to the access request and into an update area which is a storage destination of update data, and a plurality of physical pages are respectively assigned to the base area and the update area,

wherein the flash memory controller is configured to, when the data stored on the physical page of the base area belonging to any of the physical blocks is updated in response to the write request as update source data;

create update data from the update source data and the write data applied to the write request;

write the created update data to the update area which belongs to the same physical block as the update source data, and creates update area management information which associates an update source address indicating an access destination of the update source data with an update area address indicating a write destination of the update data, and if the access request is a read request and the update source data is designated in response to the read request;

search for the update area management information;

acquire the update area address; and

read the update data from the update area according to the acquired update area address.

6. The semiconductor storage device according to claim 1,

wherein each of the physical blocks is divided into a base area which is a storage destination of new write data among write data applied to the access request and an update area which is a storage destination of update data, and a plurality of physical pages are respectively assigned to the base area and the update area,

wherein the flash memory controller is configured to, when unwritten physical pages of the update area belonging to any of the physical blocks are exhausted, manage the physical block as a reclamation target physical block, and read data of the base area belonging to the reclamation target physical block and update data of the update area belonging to the reclamation target physical block respectively on a data buffer;

and

when the read frequency of data read on the data buffer is smaller than a designated value, assuming said condition is fulfilled, compress the data read on the data buffer, erase data in the reclamation target physical block from which data was read onto the data buffer, and write the data compressed on the data buffer to the reclamation target physical block from which the data was erased or to the base area of another physical block which differs from the reclamation target physical block.

7. The semiconductor storage device according to claim 1,

wherein each of the physical blocks is divided into a base area which is a storage destination of new write data among write data applied to the access request and an update area which is a storage destination of update data, and a plurality of physical pages are respectively assigned to the base area and the update area,

wherein the flash memory controller is configured to:

when all the data stored in any of the physical blocks has not been an access target for a definite period since being stored, manage, among the physical blocks, a physical block in which data has not been an access target for a definite period since being stored as a refresh target physical block, and read data in the refresh target physical block on a data buffer and

when the read frequency of data read on the data buffer is smaller than a designated value, assuming the above condition is fulfilled, compress the data read on the data buffer, erase data in the refresh target physical block from which data was read onto the data buffer, and write the data compressed on the data buffer to the refresh target physical block from which the data was erased or to the base area of another physical block which differs from the refresh target physical block.

8. The semiconductor storage device according to claim 1,

wherein the flash memory controller is configured to, when unwritten physical pages belonging to any of the physical blocks are exhausted:

manage the physical block as a reclamation target physical block;

read data in the reclamation target physical block onto a data buffer;

determine a read frequency level of data read on the data buffer;

batch-compress data with a low read frequency among the data read on the data buffer on the basis of the determination result;

erase data in the reclamation target physical block from which data was read onto the data buffer; and

write the data compressed on the data buffer to the reclamation target physical block from which the data was erased or to the physical pages of another physical block which differs from the reclamation target physical block; and

when all the data stored on a physical page which belongs to any of the physical blocks has not been an access target for a definite period since being stored;

manage the physical block as a refresh target physical block;

read data in the refresh target physical block onto the data buffer;

determine a read frequency level of data read on the data buffer;

batch-compress data with a low read frequency among the data read on the data buffer on the basis of the determination result, erases data in the refresh target physical block from which data was read onto the data buffer; and

write the data compressed on the data buffer to the refresh target physical block from which the data was erased or to the physical pages of another physical block which differs from the reclamation target physical block.

9. A data control method for a semiconductor storage device, the method comprising:

controlling, by a flash memory controller, a reading or writing operation to a plurality of flash memory chips, comprising a plurality of physical blocks, each of which is a unit of erasing data, and comprises a plurality of physical pages, each of which is a unit of reading or writing data,

wherein each of the physical blocks is divided into a base area configured to store new write data among write data and into an update area configured to update data stored in the base area, and a plurality of physical pages are respectively assigned to the base area and the update area;

receiving, by the flash memory controller, write data;

compressing, by the flash memory controller, write data to compress data; and

storing, by the flash memory controller, the compressed data into at least one physical page of the plurality of flash memory chips when a number of physical pages required to store the compressed data is smaller than a number of physical pages required to store the write data;

managing a logical address space which is an access target of an access request source by dividing the logical address space into a plurality of logical pages, and managing each of the logical pages in association with the physical pages which belong to any of the physical blocks, and when any of the logical pages is designated in response to a write request from the access request source;

selecting one, two or more of the physical pages as physical pages which correspond to the designated logical pages; and

storing compressed write data on the selected physical pages, forming a virtual physical page for storing the compressed write data as data when the compressed write data is virtually decompressed, and changing the corresponding relationship between the designated logical page and the one, two or more of the physical pages of the physical block corresponding to the logical page into a corresponding relationship between the designated logical page and the virtual physical pages;

when a logical page, which is the same as the designated logical page, is designated in response to a subsequent access request, processing the virtual physical page as an access destination;

accumulating write data which is added to each of the write requests each time a write request is received from the access request source, and batch-compressing a plurality of the accumulated write data;

when a compression effect of the compressed write data is greater than a designated value, assuming said condition is fulfilled, storing the compressed write data on the selected physical page; and

when the compression effect of the compressed write data is smaller than a designated value, assuming said condition is fulfilled, storing the write data added to each of the write requests on the selected physical page.

10. The data control method for a semiconductor storage device according to claim 9, further comprising:

managing, by the flash memory controller, a logical address space which is an access target group;

dividing, by the flash memory controller, the logical address space into a plurality of logical groups, wherein each of the logical groups is associated with the base area of each of the physical blocks;

receiving a write request designating a logical address of the logical address space;

specifying a logical group including the designated logical address;

selecting a physical block within the base area for storing the compressed write data;

storing the compressed write data into a physical page in the selected base physical block;

forming a virtual page assigned to the physical page which stores the compressed data, for managing the compressed write data as data when the compressed write data is virtually decompressed;

changing the corresponding relationship between the specified logical group and the physical page into a corresponding relationship between the specified logical group and the virtual page; and

when a logical group is designated by a subsequent access request, processing the physical page which is assigned to the virtual page as an access destination.

11. The data control method for a semiconductor storage device according to claim 9, further comprising:

when, as a result of the write data compression, the physical pages serving as write targets among the physical pages which belong to the selected physical block are reduced, reducing, by the flash memory controller, a number of physical pages assigned to the base area belonging to the selected physical block; and

increasing, by the flash memory controller, a number of physical pages assigned to the update area belonging to the selected physical block.

12. The data control method for a semiconductor storage device according to claim 9, further comprising:

comparing, by the flash memory controller, among the write data, the data size of the write data before the compression with the data size of the write data after the compression;

when the data size of the write data after the compression is smaller than the data size of the write data before the compression by at least size of the physical page, writing, by the flash memory controller, the write data after the compression to the base area; and

when the data size of the write data after the compression is not smaller than the data size of the write data before the compression by at least size of the physical page, writing, by the flash memory controller, the write data before the compression to the base area.

13. The data control method for a semiconductor storage device according to claim 9, further comprising:

when the data stored on the physical page of the base area belonging to any of the physical blocks is updated by the write request as update source data;

creating, by the flash memory controller, update data from the update source data and the write data applied to the write request;

writing, by the flash memory controller, the created update data to the update area which belongs to the same physical block as the update source data; and

creating, by the flash memory controller, update area management information which associates an update source address indicating an access destination of the update source data with an update area address indicating a write destination of the update data; and

when the access request is a read request and the update source data is designated in response to the read request;

searching, by the flash memory controller, for the update area management information, acquires the update area address; and

reading, by the flash memory controller, the update data from the update area according to the acquired update area address.

14. A storage system comprising:

a plurality of semiconductor storage devices, and

a storage controller configured to control the plurality of semiconductor storage devices as a RAID group,

wherein each of the plurality of semiconductor storage devices comprises;

a plurality of flash memory chips which comprise a plurality of physical blocks, each of which is a unit of erasing data, and comprises a plurality of physical pages, each of which is a unit of reading or writing data; and

a flash memory controller which is configured to;

control reading or writing operation to the plurality of flash memory chips;

receive write data;

compress the write data to compressed data;

store the compressed data into at least one physical page of the plurality of flash memory chips when a number of a physical page required to store the compressed data is smaller than a number of physical pages required to store the write data;

manage a logical address space which is an access target of an access request source by dividing the logical address space into a plurality of logical pages, and manage each of the logical pages in association with the physical pages which belong to any of the physical blocks, and when any of the logical pages is designated in response to a write request from the access request source;

select one, two or more of the physical pages as physical pages which correspond to the designated logical pages; and

store compressed write data on the selected physical pages, form a virtual physical page for storing the compressed write data as data when the compressed write data is virtually decompressed, and change the corresponding relationship between the designated logical page and the one, two or more of the physical pages of the physical block corresponding to the logical page into a corresponding relationship between the designated logical page and the virtual physical pages;

when a logical page, which is the same as the designated logical page, is designated in response to a subsequent access request, process the virtual physical page as an access destination;

accumulate write data which is added to each of the write requests each time a write request is received from the access request source, and batch-compress a plurality of the accumulated write data;

when a compression effect of the compressed write data is greater than a designated value, assuming said condition is fulfilled, store the compressed write data on the selected physical page; and

when the compression effect of the compressed write data is smaller than a designated value, assuming said condition is fulfilled, store the write data added to each of the write requests on the selected physical page.