Problem isolation in RAID recovery

By -

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.

Comments

Post a Comment

Popular posts from this blog

QNAP Data Recovery

By -
Image
We were doing some experiments with our QNAP TS-639: pulled off six drives storing several real shares total capacity of 7.5 TB, inserted new blank drives and created a new RAID5 over them, made new test shares, loaded the data to them, and turned off the system. When we put the old disks (with real shares) to the corresponding bays and turned on the unit, the system has booted without a problem but…our Windows 7 PC could no longer see the NAS. QFinder 6.2.0.0726 saw the NAS and reported that the QNAP had an IP address. More than that, all the shares were available in the Control panel of QFinder.   Went to the General setting in QFinder and everything looked good in there: Tried to map a network drive as described here and got the following: " Network failure: the device was not found on the network. Please check the device status. " In Windows Network we had the following: Clicked the NAS from the...
Read more

APFS Data Recovery

By -
Apple File System, APFS for short, is a brand-new filesystem released in 2017. The goal is to replace HFS+ which has been in use on Apple computers since 1998. Formally released in late 2017, APFS filesystem began to be used by default on Apple computers running under MacOS High Sierra. Among the main features of APFS filesystem are 64-bit pointers allowing to address 2^56 blocks More accurate created/accesses/modification time measured in nanoseconds since 1970-01-01 Copy-on-write Sharing blocks between APFS volumes Native full-disk encryption We are happy to announce that now ReclaiMe data recovery software is capable of recovering data from APFS-formatted devices be it a USB thumb drive, or external hard drive, or internal SSD boot drive. You can download the latest build of ReclaiMe at www.ReclaiMe.com .
Read more