Documentation/filesystems/ubifs.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 UBI File System
10 UBIFS file-system stands for UBI File System. UBI stands for "Unsorted
13 is completely different to any traditional file-system in Linux, like
14 Ext2, XFS, JFS, etc. UBIFS represents a separate class of file-systems
16 file-system of this class is JFFS2.
24 2 MTD devices support 3 main operations - read from some offset within an
26   eraseblock. Block  devices support 2 main operations - read a whole
29   re-write its contents. Blocks may be just re-written.
30 4 Eraseblocks become worn out after some number of erase cycles -
31   typically 100K-1G for SLC NAND and NOR flashes, and 1K-10K for MLC
32   NAND flashes. Blocks do not have the wear-out property.
39 file-systems.
41 UBIFS works on top of UBI. UBI is a separate software layer which may be
42 found in drivers/mtd/ubi. UBI is basically a volume management and
43 wear-leveling layer. It provides so called UBI volumes which is a higher
44 level abstraction than a MTD device. The programming model of UBI devices
45 is very similar to MTD devices - they still consist of large eraseblocks,
46 they have read/write/erase operations, but UBI devices are devoid of
49 In a sense, UBIFS is a next generation of JFFS2 file-system, but it is
53 * JFFS2 works on top of MTD devices, UBIFS depends on UBI and works on
54   top of UBI volumes.
55 * JFFS2 does not have on-media index and has to build it while mounting,
59 * JFFS2 is a write-through file-system, while UBIFS supports write-back,
62 Similarly to JFFS2, UBIFS supports on-the-fly compression which makes
65 Similarly to JFFS2, UBIFS is tolerant of unclean reboots and power-cuts.
67 journal and recovers from crashes, ensuring that the on-flash data
74 UBI, which scales linearly. So overall UBI/UBIFS stack scales linearly.
75 Nevertheless, UBI/UBIFS scales considerably better than JFFS2.
78 would scale logarithmically as well. UBI2 would support the same API as UBI,
79 but it would be binary incompatible to UBI. So UBIFS would not need to be
91 no_bulk_read (*)	do not bulk-read
114 The UBI volume to mount is specified using "ubiX_Y" or "ubiX:NAME" syntax,
115 where "X" is UBI device number, "Y" is UBI volume number, and "NAME" is
116 UBI volume name.
118 Mount volume 0 on UBI device 0 to /mnt/ubifs::
120     $ mount -t ubifs ubi0_0 /mnt/ubifs
122 Mount "rootfs" volume of UBI device 0 to /mnt/ubifs ("rootfs" is volume
125     $ mount -t ubifs ubi0:rootfs /mnt/ubifs
128 to UBI and mount volume "rootfs":
129 ubi.mtd=0 root=ubi0:rootfs rootfstype=ubifs
136 - http://www.linux-mtd.infradead.org/doc/ubifs.html
137 - http://www.linux-mtd.infradead.org/faq/ubifs.html