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FreeNAS ZFS RAIDZ2 deleted files recovery

Hardware and RAID configuration:

This is a FreeNAS 9.10 system with 4x6TB hard drives in RAIDZ2 configuration.

Problem:

The customer lost thousands of family photos and Microsoft Word documents from the NAS, probably due to accidental deletion. We recently did a similar recovery on a RAIDZ1 system. However, this is the first time we dealt with RAIDZ2.

Solution:

We came up with the following procedure to recover the deleted data:

  • Updated our algorithm to handle RAIDZ2.
  • Scanned the drives for FSO (File System Object) dnodes.
  • Filtered out file system dnodes, intermediate dnodes (ZFS uses Copy-On-Write. As a result, multiple dnodes are created when a file is created or modified), and files currently exist on the volume.
  • Used the info in the dnode to read the file header to determine the file type.
  • Recovered JPG and Docx files.

Result:

Below is an excerpt from our customer's comment:
"... I'm thrilled to report that QueTek delivered! They recovered the majority of our photos, on time, for the price they quoted. I'm so relieved. I couldn't have asked for an easier process. I hope I'm never in this situation again but, if I am, QueTek will be the first place I turn." (Full comment)


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