A larger RAID rackmount system.
Automatic RAID rebuilds fail most often because of secondary drive failure or an unrecoverable read error (URE) on a surviving disk. While RAID arrays are designed for redundancy, the rebuild process is intensive; if hardware is near its breaking point, a rebuild can certainly trigger a media failure.
In this article, we will explore the common triggers for rebuild failure and the strategic steps necessary to protect your remaining data. To speak with an expert, call 1-800-237-4200 or submit a case online.
Common Triggers for RAID Rebuild Failure
A RAID rebuild is a resource-intensive process. The controller must read every sector of the remaining healthy drives to recalculate and write the missing data to a new replacement disk.
And as every admin knows, redundancy isn’t a replacement for backup. During a rebuild, issues can push a RAID past its point of redundancy and cause permanent data loss:
- Secondary Drive Failure: In a RAID 5 array, the system can only tolerate one drive failure. If a second drive develops mechanical issues or firmware hangs during the rebuild, data loss occurs.
- Unrecoverable Read Errors (UREs): As drive capacities increase, the statistical likelihood of encountering a single bad sector grows. If the controller hits a URE on a healthy drive while trying to rebuild the array, the process will typically crash or drop the drive.
- Controller Malfunction: Sometimes the hardware controller itself fails or becomes desynchronized. If the controller writes corrupt parity data during the rebuild, it can trash the file system, making a standard mount impossible even if the hardware is repaired.
- Operator Error: Operator error remains the primary cause of RAID data loss — even when the rebuild is handled automatically. Replacing the wrong drive or inadvertently reinitializing the array are common mistakes.
Continuing to power the system or attempting to force the array online can lead to permanent data loss. If you’ve encountered a failed RAID rebuild and you need the data from the array, do not attempt a second rebuild.
An Action Plan for RAID Rebuild Failure
If your RAID rebuild has stalled or failed without a backup, follow these steps to maximize the chances of a successful data recovery.
- Power Down the System Immediately: Don’t keep the array powered on to “see if it works.” You generally have one best chance to recover data from a failing array; don’t waste the opportunity on a second rebuild.
- Label Every Drive: Before removing disks from the chassis, label them with their specific bay number (e.g., Slot 0, Slot 1).
- Document the Sequence of Events: Write down exactly what happened leading up to the failure. Which drive failed first? What did the controller log say?
- Avoid Utility Software: Do not run volume repair or file system check utilities like Chkdsk or Fsck on a degraded or failed RAID. These tools are designed to fix file system logic, not hardware-based parity issues, and they will overwrite critical data.
- Consult a Professional Data Recovery Provider: The prognosis for RAID recovery is good, even after a single rebuild failure. Look for a provider that operates laboratories with certified clean rooms, since RAID recovery almost always requires hardware repair.
Professional Resources for RAID Data Recovery
Recovering from a failed RAID rebuild requires specialized equipment and expertise. At Datarecovery.com, we utilize purpose-built systems and proprietary software to verify parity outside of the original hardware environment.
In general, we do not need your original controller to complete a recovery; we maintain an extensive hardware inventory to ensure fast turnaround times and industry-leading success rates across all RAID levels. Datarecovery.com also provides risk-free evaluations, and our RAID services include a no data, no charge guarantee.
If your RAID array is offline and a rebuild has failed, we’re here to help. Contact Datarecovery.com at 1-800-237-4200 to speak with a RAID data recovery expert or submit a case online for a free evaluation.
