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ReadyNAS - XRAID - BtrFS recovery

Hardware and RAID configuration:

A Netgear ReadyNAS device was configured with 3 drives with XRAID.

Problem:

One drive failed with head damage, the other two had read errors.

Diagnosis:

  • The data patterns and the superblock helped to determine the RAID configuration.
  • We ran an analysis and found that the parity data was intact and sufficient to rebuild the missing drive.
  • This NAS used the RAID superblock format. The data was formatted in BtrFS, a new copy on write (CoW) file system for Linux.
  • Further analysis showed that the file system was intact. Both the chunk tree and root tree were valid. The root tree pointed to other sub-volume trees which were in good condition. Most sub-volume trees pointed to the save sets of B-Tree leaf nodes which indicated that many snapshots had been taken.

Solution:

  • Using the RAID configuration found at the analysis stage, File Scavenger® can reconstruct the 3-drive RAID 5 with one missing drive. Since BtrFS was supported in File Scavenger version 5, the quick scan mode immediately detected the BtrFS volume and successfully parsed the file system.
  • Over 50 sub-volumes were found because multiple snapshots had been taken.
  • The sub-volumes with the most current data must be manually selected.

Result:

  • Three sub-volumes with the most current data were restored successfully with less than 1% corruption, mostly due to bad sectors in the two remaining drives.
  • Folder structures were completely reconstructed.


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