What to Do When a UGREEN NAS Drive Fails
If a drive makes repeated loud clicking or grinding sounds, multiple drives are missing, or UGOS Pro reports a Critical storage state, stop using the NAS. Do not initialize, format, or scan the affected drives with consumer recovery software.
One failed drive in a redundant RAID pool does not always mean the data is lost. The next step depends on the storage status, RAID level, number of affected drives, and whether the drive has physical symptoms.
Check the UGOS Pro Storage Status Before Touching a Drive
Open the Storage app and review the storage system status. This tells you whether you are dealing with an early warning, a degraded but accessible pool, or a critical failure.
| UGOS Pro status or symptom | What to do first | What to avoid |
|---|---|---|
| Normal, but errors appear intermittently | Check the affected drive’s logs, SMART data, and reconnection history | Dismissing repeated write or connection errors because SMART still passes |
| Warning | Confirm your backup and inspect the affected drive promptly | Continuing normal workloads without investigating |
| Danger | Stop nonessential workloads and protect accessible data | Removing another drive or restarting the NAS repeatedly |
| Critical, damaged, or read-only | Stop writes and preserve the current drive arrangement | Initializing, formatting, recreating, or repairing the pool without a recovery plan |
| Drive missing or repeatedly reconnecting | Record the drive’s serial number, bay, and recent logs | Moving array members between bays at random |
| Repeated loud clicking, grinding, or spin-up attempts | Shut down the NAS | Running a complete SMART scan or repeatedly powering the drive on |
A Warning means UGOS Pro has detected an issue that needs attention. A Danger status commonly indicates a degraded storage pool. Critical means the pool or storage space has suffered a serious problem, including a damaged or read-only state.
The status establishes the urgency. Whether you can still open files determines what to do next.
Protect Accessible Data Before Testing or Repairing the Pool
A degraded RAID pool can remain readable, but it is operating with reduced or exhausted fault tolerance. RAID 1 and RAID 5 have no remaining drive-failure tolerance after one member fails. A second failure before repair finishes can make the pool unavailable.
If you do not have a current independent backup:
- Pause virtual machines, containers, media indexing, synchronization, and other write-heavy tasks.
- Copy your smallest and most irreplaceable folders first.
- Prioritize documents, family photos, project files, encryption keys, and application configuration data.
- Open a sample of the copied files from the destination to confirm that the backup is usable.
- Continue with drive diagnosis only after the critical files are protected.
Do not begin by copying replaceable media or large archives while unique files remain exposed. A failing drive can deteriorate during sustained reads.
If the affected drive is making repeated mechanical noises, smells burned, or disappears during every read attempt, stop. Continuing to copy data can reduce the chance of successful professional recovery.
RAID keeps data available through the failures supported by the selected RAID level. It does not recover deleted, corrupted, or ransomware-encrypted files. For a refresher on the failure tolerance of RAID 1, RAID 5, RAID 6, and RAID 10, see our UGREEN RAID guide.
Confirm Which Drive Is Failing
In UGOS Pro, go to:
Storage > Hard Drive > HDD/SSD
Select the affected drive and record:
- Drive number and bay
- Brand and model
- Serial number
- Health status
- Temperature
- Power-on time
- Reconnection and reidentification counts
- Recent operation logs
- SMART test history
Take a screenshot of the drive details and photograph the physical bay layout before removing anything. The serial number is a more reliable identifier than remembering that “the second drive looked bad.”
DXP models provide a Locate Hard Drive function for built-in HDDs. When activated, the corresponding drive indicator changes color temporarily. DH and DH Plus models do not provide this function, so identify the disk from its drive number, slot order, serial number, and storage-pool information.
What the important SMART attributes mean
| SMART attribute or signal | What it indicates | Practical response |
|---|---|---|
| Reallocated Sector Count | The drive has replaced unreadable sectors with spare sectors | A rising count supports replacing the drive |
| Current Pending Sector Count | The drive has unstable sectors that could not be read reliably | Protect the data and treat further increases seriously |
| Offline Uncorrectable Sector Count | A scan found sectors that could not be corrected | Replace the drive after protecting accessible data |
| UDMA CRC errors | Data-transfer errors occurred between the drive and storage interface | Check the tray, bay, connection path, and logs before concluding that the disk media has failed |
| Reconnection or reidentification count | The NAS temporarily lost communication with the drive | Investigate the drive interface, bay, backplane, power, and drive together |
| Temperature | The drive’s current thermal condition | Correct blocked airflow or abnormal heat, but do not diagnose a failed drive from temperature alone |
| Power-on hours | The time the drive has accumulated in operation | Use as age and wear context, not as a universal replacement threshold |
SMART raw values and thresholds vary by manufacturer. A single raw number should not be used as a universal rule across Seagate, WD, Toshiba, and other drives. Seagate’s SMART guidance also recommends relying on the overall test result and the drive manufacturer’s diagnostic criteria.
A passing SMART result does not rule out intermittent write failures, connection problems, or sudden mechanical failure. Review the SMART result together with UGOS Pro logs and the drive’s recent behavior.
If reallocated, pending, or uncorrectable sectors are increasing, or the drive fails its manufacturer diagnostic test, order a compatible replacement immediately. Waiting until the drive stops responding extends the period during which a RAID 1 or RAID 5 pool has no remaining fault tolerance.
Do not order a replacement solely because the log records CRC or reconnection errors. Confirm the tray, bay, backplane, interface, and power path first.
Rapid test or complete test?
From the selected drive, choose Status Test and then select one of the available SMART tests:
- Rapid test: Checks basic mechanical and electrical indicators and normally completes quickly.
- Complete test: Scans the entire drive and takes considerably longer.
Run a complete test when the drive has no physical symptoms, the important data is protected, and you need deeper diagnostic evidence. Schedule it during a low-activity period.
Do not run a complete test on a drive that is clicking, grinding, repeatedly disconnecting, or holding the only copy of important files. A full scan creates sustained read activity on a device that may already be failing.
If a Drive Is Missing, Check the Connection Path Once
A missing drive does not prove that its platters or flash memory have failed. The problem can involve the drive, tray connection, bay, backplane, power delivery, or firmware communication.
Before changing anything:
- Record the missing drive’s serial number and original bay.
- Save screenshots of the storage status and recent logs.
- Shut down the NAS through UGOS Pro.
- Disconnect the power cable and wait for the NAS to stop completely.
- Confirm that the tray is assembled correctly and seated fully.
- Reinsert the same drive into the same bay.
- Reconnect power and start the NAS once.
Do not move the drive to another bay during this first check. Changing both the drive and bay makes the result harder to interpret. Never use another active RAID member as a test drive.
If the same disk disappears again, returns with write errors, or shows increasing media errors, stop using it. If several healthy drives disappear together, preserve the original bay order and contact UGREEN Support with the logs. Several simultaneous missing disks can indicate an enclosure, backplane, power, or storage-pool problem rather than independent drive failures.
If the drive reappears as unused or uninitialized, do not create a new pool on it. That operation can overwrite information needed to restore the original storage configuration.
Replace One Failed Drive When the RAID Pool Is Degraded
A degraded redundant RAID pool can usually be repaired after one failed member is replaced.
The supported failure margin is:
- RAID 1: One drive
- RAID 5: One drive
- RAID 6: Two drives
- RAID 10: One drive, or two drives when they are in different mirrored pairs
Basic, JBOD, and RAID 0 provide no drive-failure tolerance. A failed member in one of those configurations requires recovery from an independent backup or a separate data-recovery assessment.
Before replacing a RAID member:
- Protect accessible priority data.
- Confirm the failed drive’s serial number and bay.
- Check the replacement drive in the UGREEN NAS compatibility list.
- Use a replacement with capacity equal to or greater than the failed drive.
- Shut down the NAS through UGOS Pro and disconnect power.
- Remove only the confirmed failed drive.
- Install the replacement in the same bay.
- Power on the NAS and confirm that UGOS Pro recognizes the replacement as an unused drive.
A larger replacement does not immediately increase the storage pool’s usable capacity. For example, a 12TB drive can replace a failed 8TB member, but the RAID pool initially uses only 8TB of that drive. The additional 4TB remains unavailable until the other members are replaced with sufficiently large drives and the storage pool is expanded.
In Storage > Hard Drive > HDD/SSD, select the unused replacement drive and choose:
Use > Replace Storage Pool Drive
Select the degraded storage pool and confirm the operation. Do not initialize the replacement as a separate storage pool.
For tray preparation and the complete replacement sequence, follow our UGREEN NAS drive-replacement guide.
Why keeping a spare drive can matter
Most home users do not keep a replacement drive on hand. Shipping time then becomes part of the degraded period.
When a warning is tied to worsening media errors or a failed manufacturer test, order the replacement before the drive fails completely. Businesses and households that cannot tolerate this delay can keep a tested compatible spare available.
A hot spare goes one step further. When installed and assigned to a supported redundant pool before a failure occurs, UGOS Pro can use it to begin repairing the pool after an active member fails. The spare occupies an available bay and does not replace an independent backup.
A two-bay NAS using both bays for RAID 1 has no free bay for a hot spare. On larger systems, a hot spare trades one drive bay’s capacity for a shorter response time after failure.
While the RAID repair is running
A real-world test of a DXP4800 GT with four 8TB drives in RAID 5 recorded a rebuild time of approximately 10 to 15 hours after one member was replaced. Larger drives, heavier foreground activity, slower HDDs, and read errors on the surviving members can extend the process into multiple days. The measured result is an example rather than a guaranteed completion time. See the independent DXP4800 GT test.
During repair:
- Do not remove another drive.
- Do not restart or shut down the NAS unless the system requires it.
- Avoid storage expansion and RAID migration.
- Pause unnecessary write-heavy applications.
- Keep the NAS connected to stable power.
- Watch the remaining drives for new errors.
- Confirm that temperature and airflow remain normal.
A RAID 1 or RAID 5 pool has no remaining redundancy until repair finishes. RAID 6 retains protection against one additional drive failure after the first member fails.
If a configured hot spare has already started the repair, let that process finish before replacing or disabling any other member.
If the repair stalls, repeatedly restarts, or reports an error, stop experimenting and use our RAID rebuild troubleshooting guide.
Stop DIY Work When the Pool Becomes Critical
Some failure states should not proceed to ordinary drive replacement.
Stop using the NAS when:
- A drive makes repeated loud clicking or grinding sounds.
- You smell burning or see signs of electrical damage.
- The number of failed drives exceeds the RAID level’s tolerance.
- A second member fails during a RAID 1 or RAID 5 repair.
- A Basic, JBOD, or RAID 0 member fails and the data is not backed up.
- The storage pool is damaged, unavailable, or read-only.
- The drive disappears whenever data is read.
- The enclosure no longer recognizes several previously healthy drives.
- A rebuild fails and the surviving members report new errors.
Do not:
- Initialize or format any member drive
- Create a new storage pool
- Disable additional drives
- Move drives into a different order
- Run CHKDSK, filesystem repair, or consumer recovery software on individual RAID members
- Repeatedly power-cycle a mechanically failing drive
- Open the drive enclosure
- Continue a rebuild after another member begins failing
Desktop recovery applications are designed primarily for accessible standalone storage devices. An individual NAS RAID member does not contain the complete logical volume, so scanning each disk separately can produce incomplete results and create additional risk.
Preserve every member, label its original bay, and keep the drives together. UGREEN Support can help assess UGOS Pro, enclosure, and storage-pool problems from screenshots and system logs. Repeated mechanical noises, impact damage, liquid exposure, or a pool beyond its RAID tolerance require a professional recovery laboratory.
For recovery paths involving the Recycle Bin, snapshots, unavailable storage pools, encryption, or physical drive damage, see how to recover data from a UGREEN NAS.
After the Storage Pool Returns to Normal
Do not treat a completed repair as the end of the incident.
Open the Storage app and confirm that:
- The pool status is Normal.
- Every expected drive is present.
- The replacement drive belongs to the correct pool.
- No repair or synchronization task remains unfinished.
- No surviving drive reports new media or reconnection errors.
- Important folders open correctly.
- A sample restore from your independent backup succeeds.
Then review every surviving member, especially when all the drives were purchased together. Compare their:
- Power-on hours
- SMART trends
- Temperatures
- Reconnection history
- Model and firmware
- Current diagnostic results
Drives from the same purchase batch often accumulate similar operating time. One failure does not mean every sibling must be replaced immediately, but it should change how closely you watch them. Keep a compatible spare available when recovery time matters, and plan the next replacement when another member begins showing deterioration.
Enable the bad-sector warning under:
Storage > Hard Drive > Advanced Settings
Create a recurring SMART test plan under:
Storage > Hard Drive > Status Test Plan > New Plan
Schedule complete tests during low-activity periods and review trends rather than waiting for a drive to reach a failed state. Label every installed drive with its bay number so the next warning cannot turn into a wrong-drive removal.
Drive compatibility, age, temperature, unstable power, repeated connection errors, or another member beginning to show the same pattern. Our UGREEN NAS maintenance guide provides the ongoing health-check schedule.
