UBI2 : Reduction of raw flash mount time by on-flash metadata management.


  • Aruna Medhekar
  • Ruta Gadkari
  • Parul Nalavade
  • Shweta Shetty


Jitesh Shah and Vedang Manerikar

Year: 2009-2010


The project aims at optimizing the mount time of raw flash devices that use Unsorted Block Images (UBI) as the flash interface layer. It does so by introducing a new functionality of metadata management.

Currently, the metadata of the flash device is distributed over the entire device. At mount time, the entire device has to be linearly scanned to construct the flash metadata tables in RAM. Thus, the mount time is directly proportional to size of the flash device. This high mount time deters the use of UBI, in netbooks and plug computers, in which size of raw flash is significantly large.

In the proposed design, all the metadata of the flash device is stored in a group of blocks on the device. However, since the wear-leveling operation is required to be performed on the blocks, there is no fixed location on the device at which the metadata will be present at mount time. The design addresses the above constraint and maintains metadata consistency inspite of conditions like power failures, with minimal processing overheads.

In the proposed design, constructing the metadata tables at mount time requires less than 1% of the on the device to be read. This in effect, reduces the time taken for the device to initialize. The mount time is reduced to 32 to128 times of the current mount time, depending on the flash parameter. Thus, the project makes the use of large raw flash memory, with UBI feasible.