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ZFS Striped mirrored vdevs recovery

Hardware and RAID configuration:

A customer had a FreeNAS system consisting of 4x3TB drives.


The system lost the connections to the drives overnight. Attempts to import and remount the pool failed. The customer tried to reconstruct the data using File Scavenger®. Different RAID-Z configurations were tried but File Scavenger® could not locate the ZFS file system.


Our analysis showed a zpool consisting of 2 mirrored vdevs (ZFS equivalence of a RAID 10). There were minor inconsistencies in the metadata, but the directory structures and file data seemed to be intact. However, the current version of File Scavenger® could not handle a configuration with multiple vdevs.


We picked a drive from each mirror. We added custom code to File Scavenger® to extract and combine data from the two disks to reconstruct the original pool.


We were able to recover the files and directory trees in the ZFS pool (500,000 files totaling 1.7 TB).

Customer feedback:

Everything looks great! I compared files and the ones that could not open were already corrupted in the recent backup. The .nef files look great. Thank you very much and thank you again for working late and on Saturday!

John A.

More information:

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

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