METHOD AND APPARATUS FOR DETECTING STATIC DATA AREA, WEAR-LEVELING, AND MERGING DATA UNITS IN NONVOLATILE DATA STORAGE DEVICE

• US 20080147998A1
• Filed: 12/18/2007
• Published: 06/19/2008
• Est. Priority Date: 12/18/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: JEONG, Seong-hun
• Granted Patent: US 8,028,121 B2
• Time in Patent Office: Days
• US Class Current: 711/161
• 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 2212/7211 Wear leveling
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles
• CPC Class Codes: G11C 16/3495 Circuits or methods to detect or delay wearout of nonvolatile EPROM or EEPROM memory devices, e.g. by counting numbers of erase or reprogram cycles, by using multiple memory areas serially or cyclically

Abstract

Provided are a method and apparatus for wear-leveling of a nonvolatile data storage device, whereby a wear-leveling effect is maximized by storing an age value indicating a write time in each data unit of the nonvolatile data storage device and detecting a static data area based on age values. The method includes storing an age value indicating a write time in each unit assigned to write data therein, reading an age value stored in a unit, and determining a static data area based on the read age value. Accordingly, a static data area can be correctly detected without additional overhead, and a wear-leveling effect of the entire storage device can be increased by moving data to and from the static data area, thereby extending the lifespan of the storage device.

Claims

1. A method, comprising:

detecting a static data area in a nonvolatile data storage device, the detecting comprising;

storing an age value which indicates a write time in each unit assigned to write data therein;

reading an age value stored in a unit; and

determining whether the unit is a static data area based on the read age value.

2. The method of claim 1, wherein the age value indicates a relative order of when the data was written.

3. The method of claim 2, wherein the storing of the age value comprises storing the age value in a spare area of each unit.

4. The method of claim 3, wherein the age value is recorded by at least one age counter existing in the nonvolatile data storage device.

5. The method of claim 4, wherein the age counter has an age counter value and changes its age counter value every time a free unit in which no data is recorded is assigned.

6. The method of claim 5, wherein the age counter value is recorded in a spare area of a mapping table with respect to an assigned free unit and stored when the mapping table is updated.

7. The method of claim 6, wherein the age value stored is the same as the age counter value of when the data stored together with the age value was recorded.

8. The method of claim 2, wherein the reading of the age value stored in the unit is performed during an idle time of a system which drives the nonvolatile data storage device.

9. The method of claim 8, wherein the reading of the age value stored in the unit is sequentially performed with respect to all units to which data is assigned.

10. The method of claim 9, wherein the comparing of the read age value and the age counter value comprises comparing the read age value and the age counter value and if a difference between the read age value and the age counter value is greater than a predetermined threshold, determining the unit which has the read age value as being a static data area.

11. The method of claim 1, further comprising:

determining whether the unit is a static data area based on the read age value; and

wear-leveling by moving data in the unit determined as a static data area to another unit.

12. The method of claim 11, wherein the age value is recorded by at least one age counter existing in the nonvolatile data storage device, and

the age counter has an age counter value and changes its age counter value every time a free unit in which no data is recorded is assigned.

13. The method of claim 12, wherein the determining of whether the unit is a static data area based on the read age value further comprises comparing the read age value and the age counter value,

wherein, as a result of the comparison, if a difference between the read age value and the age counter value is greater than a predetermined threshold, the unit which has the read age value is detected as being a static data area.

14. The method of claim 11, wherein the moving of the data in the unit determined as a static data area to another unit comprises swapping the data of the unit determined as a static data area with the data of another unit in which other data is recorded.

15. A method of merging data units in a nonvolatile data storage device, the method comprising:

storing an age value which indicates a write time in each unit assigned to have data written therein;

reading the stored age values;

detecting a plurality of units to be merged based on the read age values; and

merging the plurality of units.

16. The method of claim 15, wherein the age value is recorded by at least one age counter which exists in the nonvolatile data storage device,

wherein the age counter has an age counter value and changes its age counter value every time a free unit in which no data is recorded is assigned.

17. The method of claim 16, wherein the reading of the stored age values is performed during an idle time of a system which drives the nonvolatile data storage device and sequentially performed with respect to all units to which the data is assigned.

18. The method of claim 17, wherein the detecting of the plurality of units to be merged based on the read age values further comprises comparing each of the read age values and the age counter value,

wherein, as a result of the comparison, if a difference between each of the read age values and the age counter value is greater than a predetermined threshold, the unit which has the read age value is detected as a unit to be merged.

19. The method of claim 17, wherein the reading of the stored age values further comprises calculating a mean value of age values of a plurality of data units with respect to a logical basic unit recognized by the system.

20. The method of claim 19, wherein the detecting of the plurality of units to be merged based on the read age values further comprises calculating computational overheads and benefits which accompany the merge,

wherein the computational overheads correspond to the amount of data to be moved during the merge and the calculated mean age value, and the benefits correspond to the amount of dirty data to be collected in a free unit due to the merge.

21. The method of claim 20, wherein the detecting of the plurality of units to be merged based on the read age values further comprises calculating priority values inversely proportional to the calculated computational overheads and proportional to the calculated benefits,

wherein a plurality of data units which have the highest priority value are detected as units to be merged.

22. An apparatus comprising:

an age recorder which stores an age value indicating a write time in each unit assigned to have data written therein;

an age reader which reads an age value stored in a unit; and

a static data determiner which determines a static data area based on the read age value.

23. The apparatus of claim 22, further comprising:

a static data detector which detects a static data area based on the read age value; and

a wear-leveling data unit transformer which moves data in the detected static data area to another unit.

24. An apparatus for merging data units in a nonvolatile data storage device, the apparatus comprising:

an age recorder which stores an age value indicating a write time in each unit assigned to have data written therein;

an age reader which reads the stored age values;

a merge object search unit which detects a plurality of units to be merged based on the read age values; and

a merge unit which merges the plurality of detected units.

25. A computer readable recording medium storing a computer readable program for executing a method comprising:

storing an age value which indicates a write time in each unit assigned to write data therein;

reading an age value stored in a unit; and

determining whether the unit is a static data area based on the read age value.