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+UBI - Unsorted Block Images
+
+UBI (Latin: "where?") manages multiple logical volumes on a single
+flash device, specifically supporting NAND flash devices. UBI provides
+a flexible partitioning concept which still allows for wear-levelling
+across the whole flash device.
+
+In a sense, UBI may be compared to the Logical Volume Manager
+(LVM). Whereas LVM maps logical sector numbers to physical HDD sector
+numbers, UBI maps logical eraseblocks to physical eraseblocks.
+
+More information may be found in the UBI design documentation:
+ubidesign.pdf. Which can be found here:
+http://www.linux-mtd.infradead.org/doc/ubi.html
+
+Partitioning/Re-partitioning
+
+ An UBI volume occupies a certain number of erase blocks. This is
+ limited by a configured maximum volume size, which could also be
+ viewed as the partition size. Each individual UBI volume's size can
+ be changed independently of the other UBI volumes, provided that the
+ sum of all volume sizes doesn't exceed a certain limit.
+
+ UBI supports dynamic volumes and static volumes. Static volumes are
+ read-only and their contents are protected by CRC check sums.
+
+Bad eraseblocks handling
+
+ UBI transparently handles bad eraseblocks. When a physical
+ eraseblock becomes bad, it is substituted by a good physical
+ eraseblock, and the user does not even notice this.
+
+Scrubbing
+
+ On a NAND flash bit flips can occur on any write operation,
+ sometimes also on read. If bit flips persist on the device, at first
+ they can still be corrected by ECC, but once they accumulate,
+ correction will become impossible. Thus it is best to actively scrub
+ the affected eraseblock, by first copying it to a free eraseblock
+ and then erasing the original. The UBI layer performs this type of
+ scrubbing under the covers, transparently to the UBI volume users.
+
+Erase Counts
+
+ UBI maintains an erase count header per eraseblock. This frees
+ higher-level layers (like file systems) from doing this and allows
+ for centralized erase count management instead. The erase counts are
+ used by the wear-levelling algorithm in the UBI layer. The algorithm
+ itself is exchangeable.
+
+Booting from NAND
+
+ For booting directly from NAND flash the hardware must at least be
+ capable of fetching and executing a small portion of the NAND
+ flash. Some NAND flash controllers have this kind of support. They
+ usually limit the window to a few kilobytes in erase block 0. This
+ "initial program loader" (IPL) must then contain sufficient logic to
+ load and execute the next boot phase.
+
+ Due to bad eraseblocks, which may be randomly scattered over the
+ flash device, it is problematic to store the "secondary program
+ loader" (SPL) statically. Also, due to bit-flips it may become
+ corrupted over time. UBI allows to solve this problem gracefully by
+ storing the SPL in a small static UBI volume.
+
+UBI volumes vs. static partitions
+
+ UBI volumes are still very similar to static MTD partitions:
+
+ * both consist of eraseblocks (logical eraseblocks in case of UBI
+ volumes, and physical eraseblocks in case of static partitions;
+ * both support three basic operations - read, write, erase.
+
+ But UBI volumes have the following advantages over traditional
+ static MTD partitions:
+
+ * there are no eraseblock wear-leveling constraints in case of UBI
+ volumes, so the user should not care about this;
+ * there are no bit-flips and bad eraseblocks in case of UBI volumes.
+
+ So, UBI volumes may be considered as flash devices with relaxed
+ restrictions.
+
+Where can it be found?
+
+ Documentation, kernel code and applications can be found in the MTD
+ gits.
+
+What are the applications for?
+
+ The applications help to create binary flash images for two
+ purposes: pfi files (partial flash images) for in-system update of
+ UBI volumes, and plain binary images, with or without OOB data in
+ case of NAND, for a manufacturing step. Furthermore some tools
+ are/and will be created that allow flash content analysis after a
+ system has crashed.
+
+Who did UBI?
+
+ The original ideas, where UBI is based on, were developed by Andreas
+ Arnez, Frank Haverkamp and Thomas Gleixner. Josh W. Boyer and
+ some others were involved too. The implementation of the kernel
+ layer was done by Artem B. Bityutskiy. The user-space applications
+ and tools were written by Oliver Lohmann with contributions from
+ Frank Haverkamp, Andreas Arnez, and Artem. Joern Engel contributed a
+ patch which modifies JFFS2 so that it can be run on a UBI
+ volume. Thomas Gleixner did modifications to the NAND layer and also
+ some to JFFS2 to make it work.