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→Memory Technology Devices (MTD)
= Memory Technology Devices (MTD) =
MTD subsystem (Memory Technology Devices) provides an abstraction layer for raw flash devices. It makes it possible to use the same API when working with different flash types and technologies (NOR and NAND in particular). Please refer to the [http://www.linux-mtd.infradead.org/doc/general.html official documentation] for detailed information.
== MTD Partitions ==
The mapping driver can either specify a hard-coded partition layout or read the partition layout from the kernel command line passed in from the boot loader. With partition support, each MTD partition will be exported as a separate MTD device. Each device has a descriptive name which can be viewed using the following command:
<pre>
cat /proc/mtd
</pre>
=== Command line configured MTD partitions ===
== UBI ==
UBI (Unsorted Block Images) is a volume management system for raw flash devices which manages multiple logical volumes on a single physical flash device and spreads the I/O load (i.e, wear-leveling) across whole flash chip. UBI/UBIFS is the recommended solution when using large flash partitions. For further information on UBI, plase refer to http://www.linux-mtd.infradead.org/doc/ubi.html == File system systems on MTD == Because of the particular characteristics of flash memory, it is best used with a specifically designed flash file systems, which handles the read/write/erase operations and the wear-leveling algorithms. At the moment there are only a few filesystems which support NAND:* JFFS2 and YAFFS for bare NAND Flash and SmartMediaCards* NTFL for DiskOnChip devices* TRUEFFS from M-Systems for DiskOnChip devices* SmartMedia DOS-FAT as defined by the SSFDC Forum* UBIFS for bare NAND flash The most common solutions are JFFS2 and UBI/UBIFS.
=== JFFS2 ===
The Journaled Flash File System v.2 provides non-volatile storing and compression of data on flash devices. For more details about is please see http://www.linux-mtd.infradead.org/doc/jffs2.html. It can be a good choice for not too big flash partitions (as a reference, not bigger than 128 MByte).
The default MTD partition associated to the NAND flash is mapped as number .... Please note that the same technique can be used with the NOR Flash partitions.