Synology NAS Error Code 16: How to Fix It

Medium 1-8 hours (varies: backup and RAID rebuild can take several hours) High Severity Verified June 2026
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Error Code
16
Brand
Synology
Product Type
nas
Severity
High
DIY Difficulty
Medium
Estimated Fix Time
1-8 hours (varies: backup and RAID rebuild can take several hours)
Synology NAS Error Code 16 indicates a disk write error within the DSM (DiskStation Manager) operating system, meaning the system was unable to successfully write data to one or more of your installed drives. This is a high-severity error that can signal failing hard drives, file system corruption, bad sectors, or a degraded RAID volume. Acting quickly is critical — continued write failures can lead to permanent data loss or a completely unreadable storage pool.
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Tools You'll Need

How to Fix Error Code 16

  1. Back Up Your Data Immediately

    Do NOT attempt to write new data to the NAS during this process. Additional write attempts on a failing drive can accelerate data loss.

  2. Check DSM Notifications and Storage Manager

  3. Run S.M.A.R.T. Tests on All Drives

    Extended S.M.A.R.T. tests can take several hours depending on drive size. Keep the NAS powered on and do not interrupt the test.

  4. Attempt a File System Check (fsck)

    A file system check will make your shared folders temporarily inaccessible. Schedule this during off-hours or low-usage periods.

  5. Check and Reseat the Drive Causing Errors

    Always power off the NAS before physically handling drives unless your model explicitly supports hot-swapping. Removing a drive while the NAS is powered in a non-hot-swap model can cause additional data loss.

  6. Replace a Failing Drive and Repair the Storage Pool

    During the RAID repair/rebuild process, the NAS is in a degraded state. If a second drive fails during a rebuild, data recovery may become impossible. Ensure your backup from Step 1 is complete before proceeding.

  7. Update DSM and Storage Drivers

  8. Monitor Logs for Recurring Errors

Parts You May Need

Compatible replacement hard drive
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Uninterruptible Power Supply (UPS)
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Drive tray or caddy
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Compatible replacement hard drive
Check Price on Amazon
Uninterruptible Power Supply (UPS)
Check Price on Amazon
Drive tray or caddy
Check Price on Amazon
Compatible replacement hard drive
Check Price on Amazon
Uninterruptible Power Supply (UPS)
Check Price on Amazon
Drive tray or caddy
Check Price on Amazon
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When to Call a Professional

Contact Synology support (support.synology.com) or a professional data recovery service if: (1) multiple drives have failed simultaneously, (2) the storage pool shows 'Crashed' status and cannot be repaired through DSM, (3) S.M.A.R.T. tests show severe errors on more than one drive, (4) the file system check fails to complete or returns unrecoverable errors, or (5) your NAS shows hardware issues such as a failed backplane or SATA controller. Professional data recovery labs (such as DriveSavers or Ontrack) can sometimes recover data from crashed RAID arrays that DSM cannot repair — but this can be costly. Do not attempt to open hard drive casings yourself, as this will void warranties and almost always causes further damage.

Frequently Asked Questions

What causes Synology Error Code 16?
Synology Error Code 16 is a DSM disk write error caused when the system fails to write data to an installed drive. The most common causes are a failing or bad-sector hard drive, file system corruption, a degraded RAID array, a loose drive connection, or in rarer cases a hardware fault in the NAS enclosure such as a faulty backplane or SATA controller.
Will I lose data because of Synology Error Code 16?
Not necessarily, but the risk is high. If the error is caught early and your RAID configuration has redundancy (such as RAID 1, RAID 5, or SHR), you may be able to replace the failing drive and rebuild the array without losing data. However, if the pool has already crashed or multiple drives have failed, data loss is possible. Always back up immediately when this error appears.
Can I fix Synology Error Code 16 without replacing a drive?
Yes, in some cases. If the error was caused by file system corruption rather than physical drive failure, running a file system check through DSM's Storage Manager may resolve it. Reseating a loose drive can also fix intermittent write errors. However, if S.M.A.R.T. diagnostics confirm the drive is physically failing, replacement is the only reliable fix.
How long does a Synology RAID rebuild take after replacing a drive?
RAID rebuild times vary significantly based on drive size and NAS model. A 4TB drive rebuild can take anywhere from 8 to 24 hours or longer. Larger drives (8TB, 12TB, 16TB) can take multiple days. During this time the NAS remains accessible but is in a degraded state — avoid heavy read/write workloads and do not power off the unit until the rebuild is complete.
How do I prevent Synology disk write errors in the future?
To reduce the risk of future write errors: (1) Enable S.M.A.R.T. scheduled tests in Storage Manager to catch drive problems early, (2) keep DSM updated to the latest firmware version, (3) use drives from Synology's official compatibility list, (4) ensure adequate ventilation around the NAS to prevent overheating, (5) use a UPS (uninterruptible power supply) to protect against power surges and sudden outages that can corrupt file systems, and (6) maintain a regular offsite or cloud backup using Hyper Backup.

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