Reclaiming Data Storage Capacity in Flash Memories

• US 20070030734A1
• Filed: 05/08/2006
• Published: 02/08/2007
• Est. Priority Date: 08/03/2005
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Wright, Barry, Sinclair, Alan
• Granted Patent: US 7,450,420 B2
• Time in Patent Office: Days
• US Class Current: 365/185.110
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 16/1847 specifically adapted to static storage, e.g. adapted to flash memory or SSD
• CPC Class Codes: G06F 2212/7202 Allocation control and policies
• CPC Class Codes: G06F 2212/7205 Cleaning, compaction, garbage collection, erase control
• CPC Class Codes: G06F 3/0605 by facilitating the interaction with a user or administrator
• CPC Class Codes: G06F 3/0608 Saving storage space on storage systems
• CPC Class Codes: G06F 3/0613 in relation to throughput
• CPC Class Codes: G06F 3/064 Management of blocks
• CPC Class Codes: G06F 3/0643 Management of files
• CPC Class Codes: G06F 3/0644 Management of space entities, e.g. partitions, extents, pools
• CPC Class Codes: G06F 3/0652 Erasing, e.g. deleting, data cleaning, moving of data to a wastebasket
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/102 External programming circuits, e.g. EPROM programmers; In-circuit programming or reprogramming; EPROM emulators

Abstract

Host system data files are written directly to a large erase block flash memory system with a unique identification of each file and offsets of data within the file but without the use of any intermediate logical addresses or a virtual address space for the memory. Directory information of where the files are stored in the memory is maintained within the memory system by its controller, rather than by the host. A type of memory block is selected to receive additional data of a file that depends upon the types of blocks into which data of the file have already been written. Blocks containing data are selected for reclaiming any unused capacity therefrom by a process that selects blocks in order starting with those containing the least amount of valid data.

Claims

1. A method of operating a non-volatile memory system with data storage cells grouped into blocks of memory cells that are erased prior to reprogramming, comprising:

maintain at least one list including blocks that individually contain an amount of valid data less than a data storage capacity of the block,

select a block from said at least one list on the basis of the amount of valid data therein relative to the amount of valid data in other blocks on said at least one list,

copy the valid data from the selected block into another block, and

thereafter erase the selected block, whereby the erased selected block becomes available for the storage of other data.

2. The method of claim 1, wherein selecting a block includes selecting the block from said at least one list only on the basis of the amount of valid data therein relative to the amount of valid data in other blocks on the list.

3. The method of claim 1, wherein selecting a block includes selecting the block from said at least one list that has the least amount of valid data therein relative to the amount of valid data in other blocks on the list.

4. The method of claim 1, wherein selecting a block from said at least one list additionally includes selecting the block from said at least one list on the basis of an amount of erased storage capacity therein relative to the amount of erased storage capacity in other blocks on said at least one list.

5. A method of operating a non-volatile memory system with storage cells grouped into blocks of memory cells that are erased prior to reprogramming, comprising:

maintain at least one list including blocks that individually contain an amount of valid data plus either obsolete data or some erased data storage capacity or both,

select a block from said at least one list by considering both the relative amounts of valid data and the erased storage capacity of the blocks on said at least one list, and

copy the valid data from the selected block into another block, and

thereafter erase the selected block, whereby the erased block becomes available for the storage of other data.

6. The method of claim 5, wherein selecting the block from said at least one list includes trading off benefits of the selected block having a low amount of valid data relative to other blocks on said at least one list and the selected block having a high amount of erased storage capacity relative to other blocks on said at least one list.

7. A method of operating a non-volatile memory system with storage cells grouped into blocks of memory cells that are erased prior to reprogramming, comprising:

maintain a first list of any blocks that individually contain an amount of valid data plus obsolete data but without erased data storage capacity,

determining whether one or more blocks exist on the first list and, if so, identifying a first block from the first list on the basis of the amount of valid data in the blocks thereon,

maintain a second list of any blocks that individually contain an amount of valid data plus some erased data storage capacity,

determining whether one or more blocks exist on the second list and, if so, identifying a second block from the second list on the basis of both the amounts of valid data and erased storage capacity in the blocks thereon,

select either the first or second block on the basis of value to operation of the memory system from reclaiming the blocks, and

copy the valid data from the selected block into another block, and

thereafter erase the selected block, whereby the selected first or second block has been reclaimed as an erased block that is available for the storage of other data.

8. A method of operating a non-volatile memory system with storage cells grouped into blocks of memory cells that are erased prior to reprogramming, comprising:

maintain a first list including any blocks that individually contain an amount of valid data plus obsolete data but without erased data storage capacity,

determining whether one or more blocks exist on the first list and, if so, identifying a first block from the first list that has the least amount of valid data of the blocks thereon,

maintain a second list including any blocks that individually contain an amount of valid data plus some erased data storage capacity,

determining whether one or more blocks exist on the second list and, if so, identifying a second block from the second list that has the least amount of valid data of the blocks thereon,

select either the first or second block on the basis of the amount of valid data contained in them after adjusting the amount of valid data in the second block for the amount of erased data storage capacity in the second block, and

copy the valid data from the selected block into another block, and

thereafter erase the selected block, whereby the selected first or second block has becomes an erased block that is available for the storage of other data.

9. A method of operating a non-volatile memory system with storage cells grouped into blocks of memory cells that are erased prior to reprogramming, comprising:

selecting a block for a reclaim operation on the basis of a content of at least some of the blocks, and

thereafter reclaiming the selected block by copying valid data of the selected block into another block and then erasing the selected block.

10. The method of claim 9, wherein selecting a block for a reclaim operation includes doing so on the basis of the content of at least some of the blocks individually including a quantity of valid data.

11. The method of claim 10, wherein selecting a block for a reclaim operation additionally includes doing so on the basis of the content of at least some of the blocks individually including an amount of erased capacity remaining in the individual blocks for the storage of data.

12. The method of claim 11, wherein selecting a block for a reclaim operation additionally includes doing so on the basis of the content of at least some of the blocks individually including no obsolete data.

13. The method of claim 9, wherein selecting a block for a reclaim operation includes doing so on the basis of the content of at least some of the blocks individually including an amount of erased capacity remaining in the individual blocks for the storage of data.

14. The method of claim 9, wherein selecting a block for a reclaim operation includes doing so on the basis of the content of at least some of the blocks individually including no obsolete data.