Flash memory controller: Difference between revisions

Revision as of 12:06, 8 July 2019

Revision as of 10:11, 22 July 2019

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{{Main|Wear leveling}}

Flash memory can withstand a limited number of program-erase cycles. If a particular flash memory block were programmed and erased repeatedly without writing to any other blocks, the one block would wear out before all the other blocks thereby prematurely ending the life of the storage device. For this reason flash controllers use a technique called [[wear leveling]] to distribute writes as evenly as possible across all the flash blocks in the SSD. In a perfect scenario this would enable every block to be written to its maximum life so they all fail at the same time.<ref name="Li-Pin Chang">{{cite web |citeseerx = 10.1.1.103.4903 |title=On Efficient Wear Leveling for Large Scale Flash Memory Storage Systems |author=Chang, Li-Pin |date=2007-03-11 |work= |publisher=National ChiaoTung University, HsinChu, Taiwan |accessdate=2010-05-31}}</ref>

==Flash Translation Layer (FTL) and Mapping==

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{{Main|Garbage collection (SSD)}}

Once every block of a solid-state storage device has been written one time, the flash controller will need to return to some of the initial blocks which no longer have current data (also called stale blocks). The data in these blocks were replaced with newly written blocks and now they are waiting to be erased so that new data can be written into them. This is a process called ''[[Garbage collection (computer science)|garbage collection]]'' (GC). All SSDs, CF Cards, and other flash storage devices will include some level of garbage collection. The speed at which a flash controller will do this can vary.<ref name="OCZ_WA">{{cite web |url=http://www.oczenterprise.com/whitepapers/ssds-write-amplification-trim-and-gc.pdf |title=SSDs - Write Amplification, TRIM and GC |author= |date= |workwebsite= |publisher=OCZ Technology |accessdate=2010-05-31}}</ref>

==References==