Synology NAS Error Code 20: How to Fix It
Medium 1 to 6 hours (depending on whether a drive replacement and rebuild are required) Medium Severity
Verified June 2026
- Error Code
- 20
- Brand
- Synology
- Product Type
- nas
- Severity
- Medium
- DIY Difficulty
- Medium
- Estimated Fix Time
- 1 to 6 hours (depending on whether a drive replacement and rebuild are required)
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Tools You'll Need
- Web browser (to access DSM web interface)
- External USB hard drive or network backup destination (for data backup)
- Phillips screwdriver (if physically replacing a drive)
- Replacement hard drive (if a failing drive is identified)
- Uninterruptible Power Supply (UPS) (recommended for prevention)
How to Fix Error Code 20
-
Back Up All Accessible Data Immediately
Do NOT attempt to write new files to the volume or run intensive applications against it while it is in read-only mode. Any write attempt will fail and may complicate recovery. -
Check Storage Manager for Drive Health Alerts
If a drive is shown as failing, do not attempt a repair on the volume until you have replaced the drive and rebuilt the RAID array (if applicable). Repairing on a failing drive can cause total data loss. -
Perform a Controlled Restart of the NAS
-
Run a File System Check (fsck) via Storage Manager
Do not power off the NAS or interrupt the check once it has started. An interrupted fsck can leave the file system in a worse state than before. -
Check and Review DSM System Logs
-
Replace a Failing Drive and Rebuild the Array (If Applicable)
Always use the DSM software shutdown before removing any drive to avoid additional file system damage. Hot-swap only if your NAS model explicitly supports it. -
Install a UPS to Prevent Future Occurrences
Parts You May Need
3.5-inch SATA hard drive
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Uninterruptible Power Supply (UPS)
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3.5-inch SATA hard drive
Check Price on Amazon
Uninterruptible Power Supply (UPS)
Check Price on Amazon
3.5-inch SATA hard drive
Check Price on Amazon
Uninterruptible Power Supply (UPS)
Check Price on Amazon
3.5-inch SATA hard drive
Check Price on Amazon
Uninterruptible Power Supply (UPS)
Check Price on Amazon
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When to Call a Professional
Contact Synology support or a professional data recovery service if: (1) the file system check fails to repair the volume and it remains read-only, (2) multiple drives show S.M.A.R.T. failures simultaneously, (3) the volume degrades to a 'Crashed' state in Storage Manager, or (4) you cannot access or copy critical files before the repair. Data recovery services can sometimes recover files from crashed volumes that DSM can no longer mount, but this is expensive and not guaranteed. Always contact Synology support (support.synology.com) first — they can remotely review logs and guide advanced repairs at no cost.Frequently Asked Questions
What does Synology Error Code 20 mean?
Synology Error Code 20 means DSM has detected a file system error on your storage volume and has automatically switched it to read-only mode. This is a protective feature that prevents further data corruption while you investigate and repair the underlying problem.
Will I lose my data when fixing Synology Error Code 20?
Not necessarily. The volume is in read-only mode, which means your existing files are still present and readable. However, you should back up all important data before running any repair operations, since fsck and drive replacement procedures carry a small risk of data loss, especially if a drive is actively failing.
How long does a Synology file system check take?
The duration depends on the size of your volume. A 1 TB volume typically takes 30–60 minutes, while a 10 TB or larger volume can take 4–12 hours or more. The NAS remains operational in read-only mode throughout the scan, and you can monitor progress in Storage Manager.
Can a power outage cause Synology Error Code 20?
Yes. Unexpected power loss is one of the most common causes of Error Code 20. When the NAS loses power without a proper shutdown, in-progress write operations are cut off, which can corrupt the file system journal and trigger a read-only mount on the next boot. Using a UPS with automatic safe-shutdown configured in DSM is the best way to prevent this.
My Synology volume is still read-only after running a file system check — what should I do?
If the built-in file system check did not resolve the issue, first check that no drives are failing in S.M.A.R.T. diagnostics. If drives are healthy, try a clean restart after the repair completes. If the volume remains read-only or transitions to a 'Crashed' state, contact Synology technical support and provide your exported system logs. In severe cases, professional data recovery services may be able to extract your files before the volume is reformatted.