Synology iSCSI data recovery

Earlier versions, up to 6.1.7-15284, of Disk Station Manager in Synology NASes used a specific technology for creating a disk space for iSCSI volumes. It was a multi-layer system involving:

  1. RAID technology which is responsible for combining physical disks into a single storage. Typically, a RAID5 is used.
  2. btrfs filesystem which is responsible for organizing disk space for iSCSI volumes. btrfs filesystem operates with files and folders.
  3. Certain files created within the btrfs filesystem are then combined into a single virtual storage which is represented to a host PC as disk space for a iSCSI LUN.

The problems can be at any of the levels above; more than that, there can be several levels damaged at once. Data recovery from a Synology involving iSCSI LUNs starts with RAID recovery either full scale (when RAID metadata is severely damaged) or reconstructing RAID on-the-fly basing on the RAID metadata records. Then the btrfs data recovery stage follows which should bring large files containing iSCSI LUN data and LUN cluster map. Finally, the LUN files should be reassembled in a specific way to reconstruct linear disk space of the iSCSI LUN volume.

How to recover data from iSCSI LUN created with DSM versions up to 6.1.7-15284 on a Synology NAS

  1. Connect Synology disks to a PC running Windows.
  2. Download, install, and launch ReclaiMe Pro from the command line specifying
    C:\Program Files\ReclaiMe Pro\start reclaimepro. exe /synology:on
  3. Check md-RAID, LVM, BTRFS as target partition types.
    4. Recovering data from an iSCSI Synology volume in ReclaiMe Pro - checking parition types.
  4. If RAID metadata is not severely damaged, you see the Synology volume under the BTRF/ZFS section or under the md-RAID/LVM. If you do not see the volume, do a full-scale RAID recovery over the Synology disk set as described here; most likely you deal with a RAID5 so choose RAID5 as a target RAID.
  5. Scan the Synology volume for files and folders (typically within the btrfs filesystem).
    6. Recovering data from an iSCSI Synology volume in ReclaiMe Pro - selecting a volume.
  6. Identify and check iSCSI LUN files:
    • EP_DAT_00000, EP_DAT_00001 and so on. Typically, they should be under the @iSCSI\EP folder
      • Recovering data from an iSCSI Synology volume in ReclaiMe Pro - checking LUN files.
    • Files under the @iSCSI\LUN folder.
      • Recovering data from an iSCSI Synology volume in ReclaiMe Pro - checking LUN files.
  7. Click the Recover Synology button. It results in saving the configuration and then launching another copy of ReclaiMe Pro to which the saved configuration is loaded automatically.
  8. Continue working with a newly launched ReclaiMe Pro. Check MBR, GPT, md-RAID, LVM, btrfs as target partition types and click Proceed.
    9. Recovering data from an iSCSI Synology volume in ReclaiMe Pro - loading the config.
  9. Identify your reconstructed Synology volume in the list of available devices, check it and click Start scan.
    10. Recovering data from an iSCSI Synology volume in ReclaiMe Pro - select a volume.
  10. Check the quality of the recovery by previewing some recovered files, preferably images like jpg, tiff, or png.
    11. Recovering data from an iSCSI Synology volume in ReclaiMe Pro - final result.
  11. Copy the recovered data.