Synology RAID Group Degraded with No Failed Drive
A Synology RAID group can be degraded even when every installed disk passes SMART because degradation reflects RAID membership, not just hardware health. A member may be absent from the active set, out of sync, timing out, or carrying metadata that DSM no longer accepts.
Do not start repair solely because all drives appear healthy. First identify which member DSM excluded and whether the surviving members can support a rebuild.
What this condition means
SMART tests report selected drive-health attributes. They do not prove that every sector is readable under rebuild load or that the RAID metadata agrees across members.
Power loss, intermittent connectivity, slot or enclosure issues, firmware changes, and latent read errors can all leave the RAID degraded without a simple red “failed drive” label.
What to record
- Synology model, DSM version, RAID type, and member count
- Storage Manager and system log messages
- Bay order, serial numbers, and current member roles
- Recent power, cabling, expansion-unit, firmware, or drive events
- Any repair or replacement already attempted
What not to do
- Select a repair target by guesswork
- Remove and reseat multiple members together
- Initialize a drive DSM offers as new
- Run extended stress tests on the only surviving set
- Continue heavy writes while degradation is unexplained
How ADR evaluates it
ADR determines why the member left the set and whether the active members are readable enough to support repair or require imaging. Logs and RAID metadata are compared with the physical order.
The appropriate path may be a controlled repair, remote reconstruction, protected imaging, or physical escalation. The dashboard label alone cannot choose among them.
What happens next
A degraded group is often recoverable and may still be online, but it has reduced protection. The cause should be established before exposing the remaining members to rebuild load.