Flash memory controller: Difference between revisions

Revision as of 18:23, 14 May 2023

Revision as of 18:44, 14 May 2023

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{{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 |authorfirst1=Feng |last1=Chen, |first2=Tian |last2=Luo, and |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 | pages=6|year=2011|url=https://dl.acm.org/doi/10.5555/1960475.1960481}}</ref>

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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{{Reflist}}

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{{Solid-state drive|state=collapsed}}

{{DEFAULTSORT:Flash Memory Controller}}

[[Category:Computer memory]]

[[Category:Solid-state computer storage]]