RAID Rebuild Failed: What to Do Next
A rebuild fails when the controller cannot complete the reads and writes required to reconstruct a member. The immediate question is not how to restart it, but why it stopped and what state the array and replacement now contain.
Do not restart the rebuild or substitute another drive until the original members, replacement, and rebuild history have been recorded.
What this condition means
Common causes include unreadable sectors on a surviving member, an unstable source drive, controller or path errors, a second member dropping, or metadata that no longer describes a consistent array.
A partially written replacement may now contain useful blocks mixed with incomplete reconstruction. It should be preserved and identified rather than treated as a blank target.
What to record
- Rebuild start time, stop percentage, and error messages
- Original failed member and replacement serial numbers
- Current slot and status of every drive
- Controller logs and read-error history
- Whether the array remains online, degraded, or offline
What not to do
- Restart the rebuild repeatedly
- Discard the original failed member or partial replacement
- Run consistency checks to “finish” the process
- Force a newly dropped member online
- Run filesystem repair on the resulting volume
How ADR evaluates it
ADR determines which members contain the strongest coverage and which array generation each represents. Unstable sources are imaged, including members the controller has already rejected.
The original and partial-rebuild states can be compared during virtual reconstruction. This avoids asking the hardware controller to make another irreversible decision.
ADR can protect and compare both states, determine which blocks each contributes, and reconstruct outside the controller. Restarting the failed rebuild may overwrite evidence that is still useful.
What happens next
A failed rebuild does not by itself end recovery. Results depend on the unreadable regions, the quality of the remaining members, and how much the failed attempt changed.