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ZFS RAID-Z recovery

Hardware and RAID configuration:

There were 3x2TB hard drives from a RAID-Z.


A customer had a RAID-Z consisting of three 2TB drives. One of the drives went bad and the RAID-Z was forced to operate in degraded mode. A technician tried to replace the bad drive but swapped out a good drive by mistake. The rebuild failed and the RAID-Z went down. The customer tried unsuccessfully to import and scrub the zpool.


We ran an analysis and found that this was a RAID-Z with single parity (equivalent to RAID 5). One drive was stale. There were some corruptions but the ZFS metadata was mostly intact.


We determined the correct RAID-Z settings and used them in File Scavenger® to reconstruct the original ZFS volume and recover the original data. File Scavenger® supports ZFS and single and double parity RAID-Z.


We were able to recover the files and directory tree in the ZFS pool (1.8 million files totaling 660 GB) using the configuration below:

  • RAID: RAID-Z single parity.
  • Number of drives: 3.
     Drive 1: missing
     Drive 2: PhysicalDrive1
     Drive 3: PhysicalDrive3

Customer feedback:

Looks great. It looks like it is retaining the mod dates as well. That is really good work. Thank you!

D. Fitzpatrick

More information:

Read the in-depth technical paper ZFS and RAID-Z recoverability and performance.

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