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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
==Flash translation layer (FTL) and mapping==
{{main|Flash file system}}
Usually, flash memory controllers also include the "flash translation layer" (FTL), a layer below the file system that maps host side or file system logical block addresses (LBAs) to the physical address of the flash memory (logical-to-physical mapping). The LBAs refer to sector numbers and to a mapping unit of 512 bytes. All LBAs that represent the logical size visible to and managed by the file system are mapped to a physical ___location (block ID, page ID and sector ID) of the Flash. As part of the [[wear leveling]] and other flash management algorithms (bad block management, read disturb management, safe flash handling etc.), the physical ___location of an LBA might dynamically change frequently. The mapping units of an FTL can differ so that LBAs are mapped block-, page- or even sub-page-based. Depending on the usage pattern, a finer mapping granularity can significantly reduce the flash wear out and maximize the endurance of a flash based storage media.<ref>{{cite web|url=http://drona.csa.iisc.ernet.in/~gopi/west10/goodson.pdf|title=Design Tradeoffs in a Flash Translation Layer|first1=Garth|last1=Goodson|first2=Rahul|last2=Iyer|archive-url=https://web.archive.org/web/20150623162937/http://drona.csa.iisc.ernet.in/~gopi/west10/goodson.pdf|archive-date=June 23, 2015}}</ref><ref>{{cite web|url=http://flashdba.com/2014/09/17/understanding-flash-the-flash-translation-layer/|title=Understanding Flash: The Flash Translation Layer|date=September 17, 2014}}</ref><ref>{{cite web|url=http://files.iccmedia.com/magazines/basfeb15/basfeb15-p25.pdf|title=New flash management architecture enables MLC for industrial storage|first=Susan|last=Heidrich|date=February 2015}}</ref> The deduplication function to eliminate redundant data and duplicate writes is also added in FTL.<ref>{{Cite conference |first1=Feng|last1=Chen|first2=Tian|last2=Luo|first3=Xiaodong|last3=Zhang | title=CAFTL: a content-aware flash translation layer enhancing the lifespan of flash memory based solid state drives |conference= FAST' 11 |
As the FTL metadata takes up its own flash space, it too needs protection in case of power loss. In addition, it is possible for the mapping table to wear out before other parts of the flash memory has, prematurely ending the life of a storage device. This is usually avoided in enterprise devices by allocating an oversized space for spares, although more durable forms of storage like [[MRAM]] has been proposed for FTL too.{{Citation needed|date=May 2023}}
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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 |publisher=OCZ Technology |access-date=2010-05-31 |archive-url=https://web.archive.org/web/20120526033947/http://www.oczenterprise.com/whitepapers/ssds-write-amplification-trim-and-gc.pdf |archive-date=2012-05-26
==References==
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