System and method for allocating data in memory array having regions of varying storage reliability

• US 9,448,883 B1
• Filed: 12/04/2012
• Issued: 09/20/2016
• Est. Priority Date: 12/04/2012
• Status: Active Grant

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Inventors: Shrader, Steven
• Primary Examiner(s): Rojas, Midys
• Assistant Examiner(s): Matin, Tasnima
• Application Number:
  US13/693,739
• Time in Patent Office: 1,386 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1044 with specific ECC/EDC distribution
• CPC Class Codes: G06F 11/1072 in multilevel memories
• CPC Class Codes: G06F 11/108 Parity data distribution in semiconductor storages, e.g. in SSD
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/7208 Multiple device management, e.g. distributing data over multiple flash devices

Abstract

A system and method are provided for efficient allocation of data in a memory array having regions of varying storage reliability. Storage locations for bands of data are selectively allocated in a manner which evenly distributes the probability of error in the data when stored in the memory array in spite of the varying storage reliability. A distribution controller is provided to effect such distribution of data to maintain a collective error rate of each data band within a preselected or predetermined range. The system and method also generally provide for storing at least a first and a second data band in different corresponding sets of storage channels. The system and method also generally provide for at least one of the data bands being stored in regions of differing reliability across the set of storage channels therefor.

Claims

1. A method for allocating data storage across a memory array having unevenly distributed regions of reliability, the method comprising:

establishing a memory array defined by a plurality of storage channels each characterized by storage regions of varying data storage reliability disposed within each said storage channel;

establishing a distribution controller coupled to said memory array for selectively assigning storage locations for a plurality of data bands to be stored in said memory array, each data band to be stored by one or more write operations; and

,

actuating said distribution controller to selectively allocate portions of each data band across a corresponding set of said storage channels, said distribution controller selectively assigning the set of said storage channels to maintain for each data band a collective error rate within a preselected range, the collective error rate being generated based on the data storage reliabilities of the storage regions for the data band portions to be stored, at least a first and a second of the data bands being thereby stored in different corresponding sets of storage channels.

2. The method as recited in claim 1 wherein each said storage channel includes a flash memory device defined by a plurality of pages, each said storage region thereof includes at least one page, and at least said first and said second data bands are stored across pages within the set of said storage channels corresponding thereto.

3. The method as recited in claim 2, wherein said first data band is stored across a different number of pages than said second data band.

4. The method as recited in claim 2, wherein corresponding portions of said first and second data bands are selectively distributed in storage regions of differing reliability responsive to said reliability.

5. The method as recited in claim 1, wherein at least one of said first and second data bands are stored on less than all storage channels of said memory array.

6. The method as recited in claim 1, wherein establishing a memory array includes establishing a redundant array of inexpensive disks (RAID) including a plurality of channels of flash devices arrayed therein and determining an error rate of storage regions of said channels of flash devices.

7. The method as recited in claim 6, wherein forming a data band includes asymmetrically selecting storage regions amongst said plurality of flash devices responsive to said determination of error rate, whereby said data bands are disparately distributed amongst said plurality of flash devices.

8. The method as recited in claim 7, wherein each said storage channel includes a plurality of sequentially writable pages including a primary page and a plurality of secondary pages, wherein said secondary pages have a higher error rate than said primary page.

9. The method as recited in claim 8, wherein asymmetrically selecting storage regions amongst said plurality of storage channels includes selecting not more than one primary page for each data band, to thereby selectively distribute primary pages amongst data bands.

10. The method as recited in claim 8, wherein asymmetrically selecting storage regions amongst said plurality of storage channels includes determining an unreliable secondary page of each of said storage channels and forming each said data band based upon said determination of unreliability to thereby selectively group storage pages of said storage channels for concurrent writing, whereby an unreliable page of one storage channel is grouped separately from unreliable portions of other storage channels.

11. The method as recited in claim 10, further comprising selectively generating a parity portion responsive to an evaluation of a predetermined combination of criteria selected from the group consisting of:

a number of pages in a data band, a number of primary pages in a data band, and a number of unreliable pages in a data band.

12. The method as recited in claim 11, wherein said parity portion includes an error correcting code (ECC) and further comprising selectively grouping a plurality of data bands to said parity portion based upon their collective error rate, and writing said parity portion to said memory array.

13. A method for allocating data storage across a memory array having unevenly distributed regions of reliability, the method comprising:

establishing a memory array defined by a plurality of storage channels each characterized by storage regions of varying data storage reliability disposed within each said storage channel;

establishing a distribution controller coupled to said memory array for selectively assigning storage locations for a plurality of data bands to be stored in said memory array, each data band to be stored by one or more write operations; and

,

actuating said distribution controller to selectively allocate portions of each data band across a corresponding set of said storage channels, said distribution controller selectively assigning the set of said storage channels to maintain for each data band a collective error rate within a preselected range, the collective error rate being generated based on the data storage reliabilities of the storage regions for the data band portions to be stored, at least one of said data bands being thereby stored in at least a first and second storage region, the first storage region being in a first of said storage channels, the second storage region having a lesser reliability than the first region and being in a second of said storage channels.

14. The method as recited in claim 13, further comprising generating a parity portion based upon a corresponding data band and writing said parity portion to said memory array, whereby said parity portion is generated to have a preselected error correction threshold responsive to an evaluation of said corresponding data band therefor.

15. The method as recited in claim 14, wherein said establishing a memory array includes establishing a redundant array of inexpensive disks (RAID), said storage channels including a plurality of flash devices, each said flash device including a plurality of pages thereof, and further comprising determining an error rate of pages of said flash devices.

16. The method as recited in claim 15, further comprising asymmetrically selecting pages amongst said plurality of flash devices to form each data band, whereby said data bands are disparately distributed amongst said plurality of flash devices.

17. The method as recited in claim 16, wherein said pages of each flash device include a primary page and a plurality of secondary pages, wherein said secondary pages have a higher error rate than said primary page.

18. The method as recited in claim 17, wherein said asymmetrically selecting pages amongst said plurality of flash devices includes selecting not more than one primary page for each data band, to thereby selectively distribute primary pages amongst data bands.

19. The method as recited in claim 17, wherein said asymmetrically selecting pages amongst said plurality of flash devices includes determining an unreliable secondary page of each of said flash devices and forming each said data band based upon said determination of unreliability to thereby selectively group pages of said flash devices for concurrent writing thereto, whereby an unreliable portion of one flash device is grouped separately from unreliable portions of other flash devices.

20. The method as recited in claim 19, further comprising selectively setting an error correction configuration of the parity portion responsive to an evaluation of a predetermined combination of criteria selected from the group consisting of:

a number of pages in said corresponding data band, a number of primary portions in said corresponding data band, and a number of unreliable portions in said corresponding data band.

21. A system for allocating data storage across a memory array having unevenly distributed regions of reliability, the system comprising:

a memory array defined by a plurality of storage channels each characterized by storage regions varying in data storage reliability within each said storage channel; and

,

a distribution controller coupled to said memory array, said distribution controller receiving data to be stored and selectively assigning storage locations for a plurality of data bands to be stored in said memory array, each data band to be stored by one or more write operations, each data band distributed across a corresponding set of storage channels, said distribution controller selectively distributing said data bands over said set of storage channels to maintain a collective error rate of each data band within a preselected range, the collective error rate being generated based on the data storage reliabilities of the storage regions for the data band portions to be stored, at least a first and a second of the data bands being thereby stored in different corresponding sets of storage devices.

22. The system as recited in claim 21, wherein said memory array includes a redundant array of inexpensive disks (RAID) including a plurality of flash devices arrayed therein, each said flash device having a plurality of storage regions thereof, wherein each said storage region includes a plurality of sequentially writable pages including a primary page and a plurality of secondary pages.

23. The system as recited in claim 22, wherein said distribution controller includes a data split module including a multiplexor selectively sending data portions of each data band to a respective flash device.

24. The system as recited in claim 23, wherein said distribution controller includes a data combination module selectively retrieving data from said memory array according to said data bands.

25. A system for allocating data storage across a memory array having unevenly distributed regions of reliability, the system comprising:

a memory array defined by a plurality of storage channels each characterized by storage regions varying in data storage reliability within each said storage channel; and

,

a distribution controller coupled to said memory array, said distribution controller receiving data to be stored and selectively assigning storage locations for a plurality of data bands to be stored in said memory array, each data band to be stored by one or more write operations, each data band distributed across a corresponding set of storage channels, said distribution controller selectively distributing said data bands over said set of storage channels to maintain a collective error rate of each data band within a preselected range, the collective error rate being generated based on the data storage reliabilities of the storage regions for the data band portions to be stored, at least one of said data bands being thereby stored in at least a first and second storage region, the first storage region being in a first of said storage channels, the second storage region having a lesser reliability than the first region and being in a second of said storage channels.

26. The system as recited in claim 25, wherein said memory array includes a redundant array of inexpensive disks (RAID) including a plurality of flash devices arrayed therein, each said flash device having a plurality of storage regions thereof, wherein each said storage region includes a plurality of sequentially writable pages including a primary page and a plurality of secondary pages.

27. The system as recited in claim 26, wherein said distribution controller includes a data split module including a multiplexor selectively sending data portions of each data band to a respective flash device.

28. The system as recited in claim 27, wherein said distribution controller includes a data combination module selectively retrieving data from said memory array according to said data bands.