Network storage devices from Synology, QNAP, Drobo, Buffalo and others, and most office servers, use RAID to spread data across several drives. When one drive fails, the device keeps working and shows a warning such as "degraded", "crashed volume", "rebuild required" or a flashing amber light. Because everything still seems to work, the warning is easy to ignore.
It should not be ignored. A degraded array has lost its redundancy. In a typical RAID 1 or RAID 5 setup, one more drive problem can make the whole volume unreadable. How you respond in the next few hours often decides whether this ends with a simple drive swap or a professional recovery.
First: RAID is not a backup
RAID protects you against a single drive failing. It does not protect against deletion, ransomware, a failed controller, a power surge that damages several drives, fire or theft. If your NAS holds the only copy of important files, treat a degraded warning as urgent.
What to do
- Reduce activity on the device. Pause heavy jobs, such as large syncs, video projects or anything writing lots of data, until you have a plan.
- Copy your most important data off first. If you do not have a recent, verified backup, copy the critical files to another drive or cloud storage now, while the array is still readable. Do this before attempting a rebuild.
- Check the health of the remaining drives. Look at the SMART status and any reallocated or pending sector counts in the NAS management page. If another drive is showing errors, a rebuild is high risk.
- Identify the failed drive carefully. Note the bay number and drive serial number reported by the NAS, and label every drive with its slot position before removing anything.
- Replace with a compatible drive of the same or larger capacity, ideally a NAS-rated model on your device's compatibility list.
- Let the rebuild finish without restarting the device. Rebuilds on large drives can take a day or more, and the array is vulnerable until it completes.
What not to do
- Do not pull the wrong drive. Removing a healthy drive from a degraded array can take the whole volume offline.
- Do not change the drive order or move drives into another device without a plan.
- Do not reinitialize, reformat or "repair" the volume when prompted, unless you are certain the data is safely elsewhere. These options can overwrite the information needed to rebuild the array.
- Do not run disk repair tools such as chkdsk or fsck on a failing array. They can make permanent changes that make professional recovery harder.
- Do not keep power-cycling a device that will not mount its volume or is making clicking or grinding noises.
Why rebuilds sometimes fail
Drives in the same NAS are often bought together, have the same age and have done the same amount of work. When one fails, the others may not be far behind. A rebuild reads every block on every remaining drive, which is exactly the kind of stress that exposes a second weak drive. That is why copying important data off before rebuilding is so valuable.
When to stop and get help
Stop and contact a data recovery specialist if more than one drive shows errors, the volume will not mount, the NAS reports a crashed or missing volume, a rebuild fails or restarts repeatedly, or any drive is making unusual noises. At that point, every extra attempt can reduce what can be recovered. Professional recovery works from images of each drive and reconstructs the array without writing to the originals.
Preventing the next scare
- Turn on email or app alerts so a degraded warning reaches someone immediately.
- Schedule regular SMART tests and data scrubbing.
- Keep at least one backup off the NAS, preferably off-site or in the cloud, and test restoring from it.
- Plan to replace drives and the device itself as they age, instead of waiting for failures.
Getting help
Our team in Burbank provides NAS and RAID data recovery, including Drobo recovery, for organizations and individuals across Los Angeles County, the Inland Empire and Ventura County. For prevention, we set up backup and disaster recovery so a single failed device is never a crisis.