Flash Translation Layer

Flash translation layer (FTL) and mapping

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 memory. 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. The deduplication function to eliminate redundant data and duplicate writes is also added in FTL.