Synology, QNAP and Asustor NAS: recovery on Btrfs / ext4 / ZFS filesystems.
Prosumer-to-enterprise NAS units (Synology DSM, QNAP QTS, Asustor ADM, Buffalo TeraStation) run modern filesystems (Btrfs, ext4, ZFS) on top of software or hardware RAID. Recovery calls for an understanding of both the vendor's proprietary stack and the underlying filesystems.
Three layers to understand.
- RAID layer: Synology Hybrid RAID (SHR/SHR-2), classic QNAP RAID, Asustor MyArchive. SHR is a special case: a mix of mdadm + LVM to support drives of different sizes.
- LVM: used by most vendors on top of the RAID to manage multiple volumes.
- Filesystem: Btrfs (Synology default), ext4 (QNAP and Asustor default), ZFS (enterprise QNAP models).
Recovery may require rebuilding any one of the three layers — it depends on where consistency broke down.
What we see most often.
- Failed drive in RAID 5/6 SHR: the classic scenario, data recovery with an mdadm/SHR rebuild.
- ZFS pool in a faulted state: often recoverable with a read-only ZFS import on an external system.
- Btrfs metadata corrupted: recovery at the btrfs-restore level or with dedicated tools. Btrfs has native recovery tools that work well as long as the damage is not too extensive.
- NAS that will not boot (corrupted NAS firmware, never the data): the data typically stays on the drives and can be read by moving them to a Linux host.
The questions we get asked most.
Do I have to ship the whole NAS or just the drives?
The drives alone are typically enough for filesystem-level recovery (we work in the lab on a Linux host, not on the NAS). If the problem is specific to the NAS firmware or to the NAS hardware itself, the NAS may be needed as well. We agree on this after the preliminary diagnosis.
Is the personal data on the NAS protected?
Yes, an NDA signed up front is standard for data recovery cases. Drives are kept in a controlled physical environment, and working copies are securely erased once recovery is complete, according to the policies agreed with you.
Does this work for very old NAS units too (e.g. a Synology DS-x10 from 8 years ago)?
Yes. The filesystems are backward compatible. On very old models the typical difficulties are physical (drives at end of life) rather than logical.