How to Replace a Failing NAS Drive Safely
When UGOS Pro flags a drive warning, a storage pool becomes degraded, or a drive repeatedly disconnects, the safest first step is to check the storage status and protect accessible data before modifying the array.
This guide explains how to identify a failing NAS drive, determine whether a single-drive replacement is safe, repair a degraded RAID pool in UGOS Pro, and recognise when to stop troubleshooting and contact technical support instead.
Quick Answer: What to Do When a NAS Drive Starts Failing
| Situation | Best Next Step |
|---|---|
| UGOS Pro displays a Warning but files are still accessible | Confirm your backup, review the affected drive and recent logs, and run diagnostics. |
| The storage pool is degraded after one drive failure | Secure essential data, identify the failed drive, prepare a compatible replacement, and use the Repair option in UGOS Pro. |
| One drive repeatedly disconnects or is intermittently missing | Record the serial number and bay slot, check the system logs, power down the NAS and reseat the drive once if there are no signs of physical damage. |
| The drive clicks, grinds or repeatedly struggles to spin up | Power down the NAS immediately to avoid stressing the drive. |
| Multiple drives are not detected, or the storage pool shows a Critical status | Keep the drives in their original bays and seek recovery or technical support before making any changes to the array |
Protect Accessible Data Before Intensive Testing or RAID Repair
If the pool is degraded but still readable and you do not have a current independent backup, protect the most important data before starting an intensive full-drive test or RAID repair, provided the affected drive is not showing physical-failure symptoms.
RAID 1 and RAID 5 each provide one-drive fault tolerance in the configurations covered here. Once one member has failed, that protection has been consumed until the array is repaired. A second required-member failure during that period can make the pool unavailable. If you need a refresher on how the RAID levels differ, see our RAID level guide.
- Pause write-heavy services: Temporarily halt virtual machines, Docker containers, media indexing and synchronisation tasks.
- Prioritise essential files: Back up irreplaceable folders first.
- Verify backup integrity: Open a sample of copied files from the destination to confirm that the backup is usable.
If you need a separate copy but have not yet established a backup workflow, our guide to NAS backup tools explains common options for home users.
If the affected drive makes repeated mechanical noises, smells burnt, disappears during read attempts or shows other signs of physical damage, do not keep reading from it simply to finish a backup. In that situation, continued reads may reduce the chance of successful professional recovery.
Identify the Exact Drive Before Removing Anything
In UGOS Pro, go to Storage > Hard Drive > HDD/SSD and open the details for the affected drive.
Record enough information to identify the physical disk unambiguously:
- Drive number and bay
- Brand and model
- Serial number
- Health status
- Temperature
- Power-on time
- Recent logs or connection history
- Any recent disconnection or bad-sector warnings
- The storage pool that uses it
Take a screenshot of the drive details and, if more than one drive may need to be removed later, photograph the bay layout. The serial number is a safer identifier than memory or tray position alone.
DXP series models support the Locate Hard Drive feature, which makes the corresponding drive indicator blink so you can identify the correct bay. DH and DH Plus models do not provide the same locate function, so identify the drive from its number, slot order, serial number and storage-pool information.
When physically removing or inserting a drive, this feature helps prevent removing the wrong one. After it is enabled, the indicator light of the corresponding slot on the NAS will turn green and blink. You can set the blinking duration, for example, to 1 minute.
When Is a Failed-Drive Replacement a Reasonable DIY Repair?
The clearest DIY replacement case is one confirmed failed member in a redundant RAID pool, with the other required members still available and no signs that the failure has spread beyond that drive.
| Storage Mode | Drive-Failure Tolerance | What One Failed Drive Means |
|---|---|---|
| RAID 1 | 1 drive | The pool can normally be repaired with a compatible replacement, but there is no remaining drive-failure tolerance until repair finishes |
| RAID 5 | 1 drive | The pool can normally be repaired after one failed member is replaced; another required-member failure before completion can make the pool unavailable |
| RAID 6 | 2 drives | After one member fails, the array still retains tolerance for one additional drive failure |
| RAID 10 | Depends on which mirrored pair is affected | A single failed member can normally be repaired; multiple-drive tolerance depends on which mirror members fail |
| Basic, JBOD or RAID 0 | No drive-failure redundancy | Replacing the failed drive does not reconstruct data from that member; recovery depends on an independent backup or a separate recovery assessment |
How to Replace One Failed Drive in a Degraded RAID Pool
Use the following workflow only when you have identified one failed member in a redundant RAID pool and the situation has not escalated into multiple-drive failure, a damaged pool or physical drive damage.
Step 1: Choose a Compatible Replacement Drive
The replacement drive must be compatible with your NAS and have a capacity equal to or greater than the smallest drive currently used in the RAID pool. Check the exact NAS model and drive model in the UGREEN NAS compatibility list before installing it. Do not assume that matching capacity alone guarantees compatibility.
If you are still deciding which HDD or SSD is appropriate for your NAS, see how to choose the correct drive for your NAS.
Step 2: Power Down Before Removing the Failed Drive
Confirm the failed drive's serial number and bay one final time. Shut down the NAS through UGOS Pro, disconnect power, then remove only the confirmed failed drive. Install the replacement in the same bay and power the NAS back on.
Step 3: Repair the Degraded Storage Pool
After startup, open the Storage app and confirm that the replacement appears as an unused drive. Then:
- Go to Storage > Hard Drive > HDD/SSD, open the replacement drive's action menu, and select Use > Repair Storage Pool when that option is available.
- Select the degraded storage pool and apply the repair.
- Follow the on-screen prompts and confirm that the replacement drive will be formatted.
- Monitor the repair until the storage pool returns to Normal.
Step 4: Let the Repair Finish Before Making Another Storage Change
RAID repair can take several hours to several days, depending on drive capacity, the amount of data, foreground workload and the condition of the surviving drives. Do not remove another member until progress reaches 100% and the pool returns to Normal.
Replacing one drive with a larger one does not immediately increase usable RAID capacity. The pool still follows the size of the smaller drives. To use the extra space, upgrade the other drives as needed, then expand the pool using a supported method.
What Should You Do While the RAID Repair Is Running?
A RAID repair performs sustained reads from the surviving members while reconstructing data onto the replacement drive. Keep the environment as predictable as possible:
- Do not remove another drive.
- Do not start storage expansion or RAID migration at the same time.
- Avoid unnecessary large transfers and write-heavy applications.
- Keep the NAS connected to stable power.
- Watch the surviving drives for new errors or disconnections.
- Keep airflow unobstructed and drive temperatures within their normal operating range.
If the rebuild stalls, repeatedly restarts, reports an error, or another RAID drive begins showing serious faults, the problem is no longer a routine single-drive replacement. Stop and assess the RAID as a broader recovery issue.
When Should You Stop DIY Troubleshooting?
Do not continue with ordinary replacement or rebuild steps when the evidence suggests physical damage, multiple-drive failure or a wider storage-pool problem.
Stop and preserve the current state when:
- A drive repeatedly clicks, grinds or struggles to spin up.
- You smell burning or see signs of electrical, impact or liquid damage.
- The number of missing or failed drives exceeds the RAID level's fault tolerance.
- A second required member begins failing during RAID 1 or RAID 5 repair.
- A Basic, JBOD or RAID 0 member fails and there is no usable backup.
- The storage pool is damaged, unavailable or read-only.
- Several previously healthy drives disappear together.
- A RAID repair fails and the surviving members begin reporting new errors.
If you encounter any of these issues, stop making changes to the RAID or storage pool and contact UGREEN technical support for further guidance.
How to Detect Drive Problems Earlier
Regular drive checks can help identify developing problems before they become more serious. You can run a one-time manual test or configure a scheduled automatic status test plan.
Manual Test
- In the hard drive list, click the ··· icon on the right and select Status test.
- In the pop-up window, click Test. The system will perform a S.M.A.R.T. test and generate a report.
- After the test is completed, you can view previous records under History.
Scheduled Automatic Test Plan
- Click the Status test plan tab in the top navigation bar, then click New plan.
- Set a plan name and select the target hard drives.
- Choose the test type, such as a rapid test or full test, and the test frequency, such as one-time or monthly.
- Schedule the test during a period of low drive activity where practical, so it is less likely to compete with normal read and write workloads.
Frequently Asked Questions
Does rebuilding RAID erase the data already on my NAS?
A normal RAID rebuild is designed to reconstruct missing redundant data onto a replacement drive, not erase the files stored on the surviving RAID members. However, a degraded array is already in a more vulnerable state, so keep an independent backup wherever possible and avoid formatting, reinitialising or recreating the storage pool during troubleshooting.
Can I shut down or restart my NAS during a RAID rebuild?
Avoid an unnecessary shutdown or restart while a rebuild is in progress. An interruption may stop reconstruction before redundancy has been restored, and behaviour after restart depends on the NAS and storage configuration. If the NAS loses power unexpectedly and the array does not resume normally, check the storage status and logs before taking further repair action.
How do I know a RAID rebuild has completed successfully?
Do not rely on the progress bar alone. After the rebuild finishes, confirm that the storage pool has returned to a healthy state, the replacement drive is recognised as a normal RAID member, and there are no new drive or storage errors in the NAS interface or system logs.
Should I replace a drive as soon as it shows S.M.A.R.T. warnings?
A single S.M.A.R.T. value does not always mean immediate failure, but persistent bad-sector warnings, repeated read errors or unexpected disconnections should not be ignored. Back up important data, review the drive's health information and replace the disk if the evidence points to deterioration. For UGREEN NAS, verify the exact replacement model in the UGREEN compatibility list before installation.
Can a RAID rebuild recover deleted or corrupted files?
No. A RAID rebuild restores redundancy after a drive failure; it is not an undelete tool or a general file-recovery process. If files were deleted, corrupted or lost because of filesystem damage, restore them from a backup or assess a suitable recovery method instead.
Conclusion
When a NAS drive starts failing, the safest sequence is to protect accessible data, identify the exact drive, confirm the RAID state, replace only the failed member, and let the storage pool repair completely. If the pool becomes Critical, multiple drives disappear, or a drive shows signs of physical failure, stop making changes to the array and contact UGREEN technical support before attempting further repair.
