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The Unsorted Block Image File System (UBIFS) is a successor to JFFS2, and competitor to LogFS,〔(【引用サイトリンク】title=UBIFS )〕 as a file system for use with raw flash memory media.〔(UBIFS does not work on top of block devices, only raw flash ), ()〕 Development began in earnest in 2007, with the first stable release made to Linux kernel 2.6.27 in October 2008.〔(UBIFS patch submission )〕 The file system is developed by Nokia engineers with help of the University of Szeged, Hungary. Note that UBIFS works on top of an unsorted block images (UBI) device, which is itself on top of a memory technology device (MTD). MTDs are not to be used directly.〔(Three layers are involved, MTD, UBI, UBIFS )〕 Two major differences between UBIFS and JFFS2 are that UBIFS supports write caching,〔http://www.linux-mtd.infradead.org/doc/ubifs.html#L_writeback〕 and UBIFS errs on the pessimistic side of free space calculation.〔(Why df reports too little free space )〕 UBIFS tends to perform better than JFFS2 for large NAND FLASH devices.〔http://www.linux-mtd.infradead.org/doc/ubifs.html#L_scalability Scalability of UBIFS vs. JFFS2〕 This is a consequence of the UBIFS design goals: faster mounting, quicker access to large files, and improved write speeds. UBIFS also preserves or improves upon JFFS2's on-the-fly compression, recoverability and power fail tolerance.〔 UBIFS's on-the-fly data compression allows zlib (deflate algorithm) or LZO. JFFS2 stores filesystem indexes in memory whereas UBIFS stores indexes in flash.〔(【引用サイトリンク】title=A Brief Introduction to the Design of UBIFS )〕 This directly impacts the scalability of JFFS2 as the tables must be rebuilt every time the volume is mounted. Also, the JFFS2 tables may consume enough system RAM that some images may be unusable. == Unsorted Block Images == Unsorted block images (UBI) is an ''erase block'' management layer for flash memory devices. UBI serves two purposes, tracking NAND flash ''bad blocks'' and providing wear leveling. Wear leveling spreads the erases and writes across the entire flash device. UBI presents logical ''erase blocks'' to higher layers and maps these to physical flash ''erase blocks''. UBI was written specifically for UBIFS so that it does not have to deal with wear leveling and ''bad blocks''. However, UBI may also be useful with squashfs and NAND flash; squashfs is not aware of NAND flash ''bad blocks''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「UBIFS」の詳細全文を読む スポンサード リンク
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