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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.


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.


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.


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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