NAS TROUBLE GUIDE
RAID rebuild failed
or stopped: what next?
A rebuild reads heavily from every surviving member. Repeating it without finding the cause can turn a degraded but recoverable array into an offline one. First identify the exact array state, preserve the bay order and decide whether the remaining drives are safe to read.
Identify where the rebuild stopped
Degraded, but rebuild never starts
The replacement may be unsupported, smaller in usable capacity, assigned incorrectly or not recognized. Record the screen before initializing or assigning it as a spare.
Failed part-way through
A surviving member may have unreadable sectors or intermittent connectivity. Repeated passes add load and can reduce the useful time left on that drive.
Inactive or Crashed
Fault tolerance may have been exceeded. Do not create a new pool, initialize members or force an array online without an evidence-preserving plan.
Rebuilding and still progressing
If there are no new errors or safety hazards, reduce workload and monitor. Do not pull a member or cut power just because the rebuild is slow.
Checks that do not alter the evidence
- Stop ordinary write activityPause recording, sync, backup jobs, downloads, databases and user writes if the management interface remains stable. Do not launch scrubs or extended tests.
- Capture the exact storage stateSave screenshots of Degraded, Rebuilding, Inactive or Crashed status, progress percentage, timestamps, error text, bay numbers and serial numbers.
- Write down every drive changeRecord which drive came from which bay and what replacement was inserted. Do not repeat removal and insertion merely to confirm.
- Verify an independent backupA snapshot in the same pool is not independent. Confirm that a copy on another NAS, USB device or cloud service actually opens.
- Choose routine repair or preservationIf the NAS contains the only copy, preserving the original members takes priority over returning the appliance to service quickly.
When to continue and when to stop
Do not do this
- Restarting the rebuild repeatedly without identifying the failure
- Running extended SMART tests, bad-block scans or RAID scrubs on stressed surviving members
- Removing drives or changing bay order while the rebuild is active
- Creating a new pool or array to make an inactive volume appear again
- Treating a Recovery command as a repair for any failed disk
- Formatting an original member or using it as the destination for recovered data
Verify against official documentation
- QNAP QTS 5.2: Storage pool statusDefinitions for Degraded, Rebuilding, Read-only and Not Active states.
- QNAP: Recovering a RAID group with Error statusConditions for recovery after temporary disconnection, distinct from disk failure.
- Synology DSM 7: Repair a storage poolOfficial degraded-pool repair requirements and replacement-drive selection.
- QNAP QTS 5.2: Rebuilding a degraded RAID groupThe model-specific workflow to consult only after the safety conditions are met.
Menu names, supported repairs, drive requirements and hot-swap behavior vary by model, firmware and RAID layout. Use the current documentation for your exact device before changing disks or array settings.
Frequently asked questions
Can I simply start the RAID rebuild again?
Do not retry until you know why it stopped. A second drive with read errors, repeated disconnects, mechanical noise, an inactive array or an unknown bay order are reasons to preserve the current state instead. A manufacturer rebuild procedure is a reasonable option only when the failure is within the array's tolerance, the remaining members appear healthy, the target bay is certain and a separate verified backup exists.
Should I turn off a rebuild that is still progressing?
If the rebuild is progressing without new errors or physical danger, do not pull drives or interrupt power arbitrarily. Reduce normal workload and follow the manufacturer's procedure. If there is smoke, a burning smell or dangerous heat, personal and fire safety overrides data-preservation guidance.
Does a button labelled Recover repair a failed drive?
Not necessarily. For example, QNAP documents RAID recovery for specific error states such as temporarily disconnected members; it is not a general repair for a physically failed disk. Record the exact status and consult the documentation for that model and firmware before using a recovery command.
Is equal drive capacity enough for a replacement?
No. Check the NAS compatibility list, actual usable capacity, drive type, sector format and the requirements of the specific RAID layout. A nominally equal replacement can still be too small or unsupported.
PRESERVE THE ORIGINAL STATE
Record first. Change nothing you cannot undo.
Photograph the status screen, bay order, drive labels and exact error message before seeking model-specific support or a professional evaluation.
See all English safety guides →Scope: HDD/SSD NAS and RAID appliances · Last reviewed: August 28, 2026