What to Do if a RAID 1 Rebuild Stops Due to an Unrecoverable Read Error on the Source Drive

Applicable Products

All QNAP NAS models

Scenario

During a RAID 1 rebuild, an unrecoverable read error on the source drive that remains in the RAID group may stop the rebuild and leave the storage pool or volume in a Degraded state. Even if the replacement drive shows Good, this does not mean that it is safe to start the rebuild again.

In this case, the RAID 1 rebuild on the NAS stopped after the source drive reported UNRECOVERED READ ERROR / Medium error. The storage pool remained accessible through the old drive, which had a SMART warning. Although the replacement drive showed Good, the rebuild screen showed no available disks.

Solution

At this point, prioritize protecting any data that is still readable and ask QNAP Support to assess the next steps.

Back Up Readable Data Immediately

If you do not have a confirmed backup and the data on the NAS is still readable, immediately back up important data to a destination outside the NAS, such as an external storage device, another NAS, or a cloud backup service with appropriate retention and restore capabilities. If you already have a backup, confirm that the latest backup completed successfully and that its files can be accessed or restored.

1. Prioritize data that cannot be replaced or obtained again.
2. Store the backup outside the current RAID group so that a failure of the source storage pool does not also make the backup inaccessible.
3. After the backup completes, check the job log and open or restore sample files to verify that the backup is usable.

Important
RAID 1 provides drive redundancy; it is not a substitute for data backups. If the array is degraded or a source drive has read errors, another drive failure may make the data inaccessible.

Note
Real-time synchronization is not necessarily equivalent to a backup with version retention. Confirm that the destination retains recoverable older versions and that the latest synchronization or backup completed successfully.

Contact QNAP Support

After backing up as much data as possible, contact QNAP Support to confirm the next steps. Provide the NAS model, QTS version, storage pool and RAID status, drive bay locations and replacement sequence, relevant error messages, and SMART or system logs so that Support can assess the situation.

Until you receive instructions from Support, avoid repeatedly starting the RAID rebuild, removing or reinserting drives, initializing or formatting drives, deleting the storage pool, or manually modifying the RAID. These actions may increase the risk of making the data unrecoverable. Keep the drives in their original bay positions and preserve the current configuration as much as possible.

Maintain Regular Backups

Schedule regular backups to a destination outside the NAS and enable an appropriate version-retention or rotation policy. Check backup jobs regularly and test file restoration. Do not wait until a drive fails or a RAID group becomes degraded to start backing up your data.