Knowledge about FTL

23 Mar

Flash Translation Layer FTL (Flash translation layer)

The operating system is usually data (512b) is written in accordance with the sector size. Unfortunately, flash read and write in the page (4KB) and flash memory erase operation is in accordance with the block (block = 128 to 256), more terrible must first erase before write data, but also to that is, can not cover, which has brought trouble to our existing file system, it is clear need for more advanced more tedious file system to solve this problem.

In order to alleviate the burden of the operating system (do not use less sophisticated file system), we can use the software to the NAND operation habits virtual into the independent sector operations (512B), so it appears the FTL Flash Translation Layer. It exists in the file system and the physical media (NAND FLASH). With this layer conversion layer, the operating system can be operated in accordance with the sector, do not worry encountered before the erase / read / write problem. All logical-to-physical translation package all FTL layer.

FTL algorithm, the truth is a logical-to-physical mapping, therefore, when the file system sends instructions say to write or update a specific logical page, FTL fact written to a different free physical page and update the mapping table (logical to physical mapping of the association), and the “old data” included on this page is marked as “invalid”. (Updated files have been written to the new address, the old address file is invalid naturally). Can be said to have FTL, we can operate like the usual mechanical hard as. Obviously FTL conversion speed directly affects the read and write performance of the SSD.

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