Monday, 19 September 2011

Problem isolation in RAID recovery

A full, start-to-end RAID recovery is generally a three part process.


  1. Determine status of the member disks and make clones when required.
  2. Detect RAID parameters and perform destriping
  3. If the destriped volume is not readily mountable, perform filesystem recovery on it to pump out the data

Now, if the above three steps fail to produce correct data, the question is how do we tell if it is RAID recovery part, or filesystem analysis part that failed?

We tell if the RAID recovery is OK by looking at the sizes of the recovered files. If there are multiple good files recovered which are larger than twice the full row size (i.e. larger than 2 * block_size * num_disks), then the RAID recovery is almost certainly OK. However, if all good files are of the small size, the RAID parameters should be investigated. This also applies to the files found by raw scan; however, keep in mind that file sizes produced by raw scan are not reliable.

No comments:

Post a Comment