Storage device employing a flash memory

• US 5,644,539 A
• Filed: 11/25/1992
• Issued: 07/01/1997
• Est. Priority Date: 11/26/1991
• Status: Expired due to Term

• Current Assignee: Emergence Memory Solutions LLC
• Original Assignee: Hitachi, Ltd.
• Inventors: Hayashi, Yoshihiro, Katayama, Kunihiro, Yamagami, Hajime, Furuno, Takeshi, Terada, Kouichi, Kaki, Kenichi, Tsunehiro, Takashi
• Primary Examiner(s): Nguyen, Viet Q.
• Application Number:
  US07/981,438
• Time in Patent Office: 1,679 Days
• Field of Search: 365/900, 365/230.01, 365/189.01, 365/200, 365/185.33, 365/185.01, 395/430, 371/10.1, 371/10.2, 371/21.1, 371/21.2
• US Class Current: 365/200
• CPC Class Codes: G06F 2212/2022 Flash memory
• CPC Class Codes: G06F 3/0601 Interfaces specially adapted for storage systems
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/0664 at device level, e.g. emulation of a storage device or system
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G11C 16/102 External programming circuits, e.g. EPROM programmers; In-circuit programming or reprogramming; EPROM emulators
• CPC Class Codes: G11C 29/765 in solid state disks

Abstract

A semiconductor disk wherein a flash memory into which data is rewritten in block unit is employed as a storage medium, said semiconductor disk comprises a data memory in which file data are stored, a substitutive memory which substitutes for blocks of errors in the data memory, an error memory in which error information of the data memory are stored, and a memory controller which reads data out of, writes data into and erases data from the data memory, the substitutive memory and the error memory. Since the write errors of the flash memory can be remedied, the service life of the semiconductor disk can be increased.

Claims

1. A storage device employing a flash memory, comprising:

a storage area comprised of (1) a plurality of data memory areas for storing data, each of said plurality of data memory areas being identified by a unique physical address, (2) a plurality of substitutive memory areas for use as substitute memory areas for said data memory areas, each of said plurality of substitutive memory areas being identified by a unique physical address, and (3) a plurality of error memory areas each of which is provided in correspondence with a respective one of said plurality of data memory areas and each of which stores error information of corresponding ones of said data memory areas, said storage device further comprising;

address conversion means; and

a memory controller which accesses a respective data memory area identified by a received physical address,

wherein at least one of said error memory areas corresponds to a data memory area in which no error occurred and stores, as said error information, information showing that no error occurred in the corresponding data memory area,

wherein each of remaining ones of said error memory areas corresponds to a respective data memory area in which error occurred and stores, as said error information, said physical address of a respective substitutive memory area to be used in place of the corresponding data memory area in which error occurred, and

wherein when the physical address of said substitutive memory area is stored as the error information in the error memory area corresponding to the data memory area identified by the physical address, said address conversion means converts said physical address, to be provided to the memory controller, into the physical address of said substitutive memory area stored in the error memory area corresponding to the respective data memory area identified by the physical address to be accessed.

2. A storage device employing a flash memory according to claim 1, wherein said storage area further comprises an initialization information area which stores start addresses and storage capacities of the respective memory areas therein.

3. A storage device employing a flash memory according to claim 2, wherein said storage capacities of said data memory area and said substitutive memory area are variable.

4. In a storage device which employs a flash memory, and to which a host system is connected, the improvement therein comprising the fact that a size of a block, which is a rewriting unit of said flash memory, is equal to a size of a sector which is an accessing unit of a file when said host system accesses the file.

5. A storage device employing a flash memory, comprising:

a storage area of said storage device, said storage area including;

a plurality of data memory areas for storing data, each of said plurality of data memory areas being identified by a unique physical address;

a plurality of substitutive memory areas for use as substitute memory areas for said data memory areas, each of said plurality of substitutive memory areas being identified by a unique physical address, and

a plurality of error memory areas each of which is provided in correspondence with a respective one of said data memory areas, and each of which stores error information of corresponding ones of said data memory areas;

said storage device including;

logical address conversion means, supplied with logical addresses in a data access operation, for converting a logical address into the physical address of the data memory area designated by the logical address, and

a memory controller which receives said physical address resulting from the conversion, and which accesses the data memory area identified by the received physical address;

wherein at least one of said error memory areas corresponds to a data memory area in which no error occurred, and stores, as said error information, information showing that no error occurred in the corresponding data memory area,

wherein each of remaining ones of said error memory areas corresponds to a respective data memory area in which error occurred, and stores, as said error information, said physical address of a respective substitutive memory area to be used in place of the corresponding data memory area in which error occurred, and

wherein when the physical address of said substitutive memory area is stored as the error information in the error memory area corresponding to the data memory area identified by the logical address, said logical address conversion means converts said logical address into the physical address of said substitutive memory area stored in the error memory area corresponding to the respective data memory area identified by the logical address, instead of converting the logical data into the physical address of said respective data memory area identified by the logical address.

6. A storage device employing a flash memory according to claim 5, wherein said error memory area, corresponding to the data memory area in which an error occurred, stores, in the event of occurrence of an error, in the substitutive memory area which is for use as a substitute for said data memory area said physical address of said substitutive memory area, which is a newly used substitute for said data memory area, as said error information.

7. A storage device employing a flash memory according to claim 5,

wherein said storage area further comprises a substitution managing area for storing information indicating those of said substitutive memory areas actually being used as substitutes therefor of respective data memory areas.

8. A storage device employing a flash memory according to claim 5, wherein a part of said data memory area is used as said substitutive memory area.

19. A storage device employing a flash memory according to claim 5, comprising:

an electrical interface which is identical to that magnetic disk, and which accepts electric signals identical to those for operating said magnetic disk.

20. A storage device employing a flash memory according to claim 5, wherein a host system is connected to the storage device, and wherein a size of said physical sector is equal to a size of a sector which is an accessing unit of a file when said host system accesses the file.

21. A storage device employing a flash memory according to claim 5, wherein said flash memory is a flash memory chip.

9. A storage device employing a flash memory, wherein a storage area of said storage device is divided into a plurality of physical sectors identified by physical addresses, said storage device includes:

logical address conversion means which receives a logical address of data in a data writing operation and converts said logical address into a physical address, and

a memory controller for receiving said physical address resulting from the conversion by the conversion means, and writing said data into a respective physical sector;

wherein said logical address conversion means converts a logical address received in the writing operation to the physical address which is different from the physical address to which said logical address conversion means converted a logical address, identical to the logical address to be presently converted, in a preceding writing operation.

10. A storage device employing a flash memory according to claim 9, further comprising:

logical address reference means for registering a correspondence between a respective logical address and a respective physical address identifying the physical sector into which data is written in the most recently performed data writing operation of the logical address; and

physical address reference means for registering information indicating a physical address identifying a physical sector which is not storing data,

wherein said logical address conversion means converts a respective logical address into a physical address corresponding thereto with referring to said logical address reference means in data reading operations and converts the logical address received in the writing operation to the physical address registered in said physical address reference means.

11. A storage device employing a flash memory according to claim 9, further comprising:

erase operations reference means for storing a number of erase operations of respective erasing sector groups each of which comprises one or more physical sectors erased together in one erasing operation when erasing data stored in the physical sector included in the erasing sector groups, and

erasing control means for erasing the erasing sector groups in the erasing operations, referring to said erase operations reference means, in which the number of erasing operations performed by the erasing sector groups are averaged.

12. A storage device employing a flash memory according to claim 11,

wherein each of said erasing sector groups includes a plurality of physical sectors, and

wherein said erasing control means comprises:

selecting means for selecting the erasing sector group including a first physical sector which is the physical sector storing data corresponding to the logical address being equal to the logical address of another data stored in another physical sector, said another data was written after the data was written into said first physical sector,

erase operations management means for exchanging the data between said erasing sector group selected by said selecting means and another erasing sector group when the number of erase operations of said erasing sector group selected by said selecting means is larger than a predetermined number, said another erasing sector group being selected from the erasing sector groups whose numbers of erase operations are equal to or smaller than said predetermined number, and

erasing means for erasing, when the number of erase operations of said erasing sector group selected by said selecting means is larger than said predetermined number, the easing sector group selected by said selecting means and for increasing the number, in said erase operations reference means, of erase operations of said erasing sector group erased by the erasing means.

13. A storage device employing a flash memory according to claim 9, further comprising:

status reference means for storing status information indicating a status in which the physical sector is filled up with written data and a status in which no data is writable due to deterioration of the physical sector, for each of said physical sectors,

wherein said logical address conversion means converts the logical address received in the writing operation to the physical address identifying the physical sector which is not in said statuses, referring said status reference means.

14. A storage device employing a flash memory according to claim 9, further comprising:

a write sector pointer for storing said physical address of the physical sector into which data should be written in the next data writing operation,

wherein said logical address conversion means converts said logical address into said physical address stored in said write sector pointer.

15. A storage device employing a flash memory according to claim 10,

wherein said physical address reference means is nonvolatile storage means, said logical address reference means is volatile storage means, and said physical address reference means further registers a correspondence between the logical address and physical address designating the physical sector into which data is written in the most recently performed data writing operation of the logical address, and

wherein said storage device further comprises control means for registering, at initialization of said storage device, said correspondence registered in said physical address reference means into said logical address reference means.

16. A storage device employing a flash memory according to claim 12,

wherein said erasing sector group includes a plurality of physical sectors, and

wherein said erasing means comprises:

storage means for temporarily saving the data including data which is stored in the physical sectors, other than said first physical sector, including in said erasing sector group selected by said selecting means, when the number of erase operations of said erasing sector group selected by said selecting means is not larger than said predetermined number,

means for erasing said erasing sector group selected by said selecting means after said storage means saves said data and for increasing the number, in said erase operations reference means, of erase operations of said erasing sector group which is erased, and

means for writing back said data which was stored in the physical sectors, other than said first physical sector,included in said erasing sector group selected by said selecting means, into said selected erasing sector group selected by said selecting means from said storage means.

17. A storage device employing a flash memory according to claim 16, wherein the data to be written is temporally stored in a part of said storage means.

18. A storage device employing a flash memory according to claim 11,

wherein said erasing sector group comprises only one physical sector, and

wherein said erasing control means comprises:

selecting means for selecting the erasing sector group comprising a first physical sector which is the physical sector storing data corresponding to the logical address being equal to the logical address of another data stored in another physical sector, said another data was written after the data was written into said first physical sector,

erasing means for erasing, when the number of erase operations of said erasing sector group selected by said selecting means is larger than said predetermined number, the easing sector group selected by said selecting means and for increasing the number, in said erase operations reference means, of erase operations of said erasing sector group erased by the erasing means, and

erase operations management means for replacing the data to said erasing sector group selected by said selecting means from another erasing sector group when the number of erase operations of said erasing sector group selected by said selecting means is larger than a predetermined number, said another erasing sector group being selected from the erasing sector groups whose numbers of erase operations are equal to or smaller than said predetermined number.