![]() In practice, flash file systems are used only for Memory Technology Devices (MTDs), which are embedded flash memories that do not have a controller. The basic concept behind flash file systems is: when the flash store is to be updated, the file system will write a new copy of the changed data over to a fresh block, remap the file pointers, then erase the old block later when it has time. Such file systems include JFFS2 and YAFFS.īecause of the particular characteristics of flash memory, it is best used with either a controller to perform wear leveling and error correction or specifically designed flash file systems, which spread writes over the media and deal with the long erase times of NAND flash blocks. ![]() Log-structured file systems have all the desirable properties for a flash file system. Wear leveling: flash memory devices tend to wear out when a single block is repeatedly overwritten flash file systems are designed to spread out writes evenly.Flash memory devices impose no seek latency. Random access: general-purpose file systems are optimized to avoid disk seeks whenever possible, due to the high cost of seeking.The time taken to erase blocks can be significant, thus it is beneficial to erase unused blocks while the device is idle. Erasing blocks: flash memory blocks have to be explicitly erased before they can be written to.While a block device layer can emulate a disk drive so that a general-purpose file system can be used on a flash-based storage device, this is suboptimal for several reasons:
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