Network Attached Storage (NAS) devices often utilize some form of RAID (Redundant Array of Independent/Inexpensive Disks) for redundancy. A single hard drive (or solid-state drive) failure will not cause immediate data loss — the failed drive can be swapped out to rebuild the RAID, provided that multiple hard drive failures have not occurred.
However, redundancy is not backup, and NAS rebuilds can fail. In fact, because rebuilds put a high amount of stress on the physical media, the chances of a second drive failure are much higher during the rebuild process than during normal operation.
Below, we’ll explain more about failed NAS rebuilds and provide an overview of the data recovery process. For a free NAS data recovery estimate, call 1-800-237-4200 or submit a case online.
What Is a Failed NAS Rebuild?
A NAS rebuild is a process that occurs when a hard drive in a RAID array fails. The RAID system is designed to protect data by distributing it across multiple drives. When one drive fails, the NAS attempts to rebuild the data onto a new or spare drive using the parity information stored on the remaining drives.
A failed NAS rebuild happens when this rebuilding process is interrupted or unsuccessful. This can occur due to various reasons, including:
- Multiple Disk Failures: If more than one drive fails during the rebuild process, the RAID system may not have enough redundancy to recover the data.
- Bad Sectors on the Replacement Drive: If the new drive used for the rebuild has bad sectors, it can prevent the data from being written correctly, causing the rebuild to fail.
- Power Interruptions: A power outage or surge during the rebuild process can disrupt the data transfer.
- Overheating: Excessive heat can damage hard drives and interfere with the rebuild process.
- Software or Firmware Issues: Bugs in the NAS software or firmware can also cause rebuild failures.
- Controller Failure: The RAID controller is responsible for managing the rebuild process. If it malfunctions, the rebuild will likely fail.
A failed NAS rebuild can lead to data loss due to irrecoverable parity data, corruption, or drive degradation. In most instances, data recovery is possible — but it’s extremely important to turn off the power to the NAS as soon as possible. Operating a NAS after a failed rebuild can permanently overwrite data, even if a second rebuild is not attempted.
Related: NAS Data Recovery: Common Failure Scenarios
Failed NAS Rebuilds for Different RAID Levels
The impact of a failed NAS rebuild can vary depending on the RAID level used:
- RAID 0: RAID 0 offers no redundancy. If one drive fails, all data is lost. A rebuild is not possible in this configuration (and RAID 0 is arguably not a “true” RAID for this reason).
- RAID 1: RAID 1 mirrors data across two drives. If one drive fails, the data is still available on the other drive. A rebuild simply involves copying the data to a new drive. A failed rebuild in RAID 1 is less catastrophic, but still results in the loss of redundancy until the rebuild is complete.
- RAID 5: RAID 5 uses parity information distributed across all drives. It can tolerate one drive failure. A failed rebuild in RAID 5 can lead to complete data loss if another drive fails before the rebuild is completed.
- RAID 6: RAID 6 is similar to RAID 5 but uses dual parity, allowing it to tolerate two simultaneous drive failures. A failed rebuild in RAID 6 is less risky, but data loss is still possible if more than two drives fail or if the rebuild fails for another reason.
- RAID 10: RAID 10 combines mirroring and striping. It offers high performance and fault tolerance. A failed rebuild in RAID 10 is less likely to result in data loss unless multiple drives fail within the same mirrored pair.
Related: RAID 10, Explained: Should You Use It?
Data Recovery Options for NAS Devices After a Failed Rebuild
Recovering data from a NAS after a failed rebuild can be complex and requires specialized tools and expertise. Once again, we strongly recommend disconnecting the power from a failed NAS. Contact a professional data recovery provider as soon as possible.
Datarecovery.com offers specialized data recovery services for NAS devices, including those affected by failed rebuilds. Our laboratories have advanced hardware imaging tools, firmware repair tools, data recovery clean rooms, and the industry’s most extensive library of storage media parts and RAID controller cards.
We support all NAS data recovery cases with a no data, no charge guarantee: If we’re unable to restore the files you need, you don’t pay for the failed attempt.
To learn more, visit our NAS data recovery page or set up a case online. If you’d like to speak directly with a RAID recovery expert, call 1-800-237-4200.
