Synology NAS Error Code 25: How to Fix It

Easy 15–30 minutes to monitor and configure; scrubbing itself may run 2–48+ hours depending on array size Medium Severity Verified June 2026
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Error Code
25
Brand
Synology
Product Type
nas
Severity
Medium
DIY Difficulty
Easy
Estimated Fix Time
15–30 minutes to monitor and configure; scrubbing itself may run 2–48+ hours depending on array size
Synology NAS Error Code 25 indicates that DSM (DiskStation Manager) is actively performing a RAID scrubbing operation on your storage pool. RAID scrubbing is a routine maintenance process that scans all drives in your array for data inconsistencies, silent corruption, and parity errors — and corrects them automatically where possible. This is not a failure alert; it is a healthy, expected maintenance event, but it does consume disk and CPU resources, so understanding it helps you manage your NAS performance during this period.
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Tools You'll Need

How to Fix Error Code 25

  1. Confirm the Scrubbing Status in DSM

  2. Check Estimated Completion Time

  3. Verify No Additional Drive Errors Are Present

    Do NOT power off your NAS while RAID scrubbing is in progress. Interrupting the scrub may leave your array in an inconsistent state and could increase risk of data loss if a drive fails at that moment.

  4. Run a S.M.A.R.T. Test if Drive Warnings Appear

  5. Review the System Log for Scrubbing Errors

  6. Pause or Reschedule Scrubbing If Performance Is Impacted

    Pausing scrubbing is safe but postpones data integrity checking. Resume the scrub as soon as possible to ensure your data remains consistent.

  7. Ensure Adequate Cooling and Ventilation During Scrubbing

  8. Back Up Critical Data Immediately If Drive Errors Were Found

    Never rely on RAID alone as a backup strategy. RAID protects against drive failure, not accidental deletion, ransomware, or simultaneous multi-drive failure.
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When to Call a Professional

Contact Synology support or a data recovery professional if: (1) one or more drives have failed during the scrub and your RAID array is degraded, (2) you see repeated 'Unrecoverable Read Error' messages in the logs, (3) the storage pool status changes to 'Degraded' or 'Crashed' during scrubbing, or (4) scrubbing has been stuck at the same percentage for more than 24 hours without progress. If the array crashes and you cannot access your data, do not attempt to rebuild the array manually without professional guidance, as incorrect steps can result in permanent data loss.

Frequently Asked Questions

Is Synology Error Code 25 serious or dangerous?
No, Error Code 25 by itself is not serious. It simply means your Synology NAS is running a scheduled RAID scrubbing operation, which is a normal and healthy maintenance process. It is only concerning if the scrub also reveals actual drive errors or parity inconsistencies that cannot be automatically repaired.
How long does Synology RAID scrubbing take?
The duration depends on the total size of your storage pool and the speed of your drives. A smaller 4–8TB pool might complete in 4–12 hours, while a large 20TB+ pool can take 24–72 hours or more. Scrubbing runs in the background and your NAS remains accessible during the process, though performance may be reduced.
Can I stop or pause RAID scrubbing on my Synology NAS?
Yes. You can pause scrubbing in DSM by going to Storage Manager > Storage Pool > selecting your pool > Action > Pause Data Scrubbing. It is safe to pause temporarily, but you should resume and complete the scrub as soon as possible. Leaving scrubbing permanently paused means your data integrity is not being verified.
How often should I run data scrubbing on my Synology NAS?
Synology recommends running data scrubbing at least once a month on all RAID storage pools. You can configure an automatic scrubbing schedule in DSM under Storage Manager > Storage Pool > Schedule Data Scrubbing. Monthly scrubs help catch silent data corruption (bit rot) before it accumulates and causes data loss.
What happens if Synology finds parity errors during scrubbing?
If the scrub finds parity inconsistencies, DSM will automatically attempt to repair them using the redundant data in your RAID array. You will see a log entry like 'Parity inconsistency found and corrected.' This is a normal outcome and means the system is working as intended. However, if errors are unrecoverable — usually due to a failing drive — DSM will alert you and you should replace the affected drive promptly.

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