Synology NAS Error Code 27: How to Fix It

Medium 1–2 hours of active work (plus several hours for SMART tests, scrubbing, and RAID rebuild running in background) Medium Severity Verified June 2026
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Error Code
27
Brand
Synology
Product Type
nas
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
1–2 hours of active work (plus several hours for SMART tests, scrubbing, and RAID rebuild running in background)
Synology DSM Error Code 27 means that one or more hard drives in your NAS have developed bad sectors — physical or logical areas of the disk that can no longer reliably store data. This is a medium-severity warning that should not be ignored, as bad sectors can spread and eventually lead to complete drive failure and data loss. Acting quickly by running diagnostics, checking your RAID health, and replacing the affected drive if necessary will protect your stored files.
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Tools You'll Need

How to Fix Error Code 27

  1. Back Up Your Data Immediately

    Bad sectors can indicate imminent drive failure. If you do not have a current backup, creating one is your top priority before attempting any repairs.

  2. Identify the Affected Drive in DSM

  3. Run a S.M.A.R.T. Quick Test

  4. Run a S.M.A.R.T. Extended Test

    Do not interrupt the extended test once started, as this can cause additional stress on an already weakened drive.

  5. Run a Storage Pool Scrubbing

    Scrubbing is read-intensive. Avoid heavy NAS workloads during this process.

  6. Check Drive Firmware and DSM Updates

  7. Check and Re-seat the Drive Connections

    Always shut down the NAS through DSM first, then unplug the power cord before removing any drives. This prevents data corruption and protects you from electrical hazards.

  8. Replace the Failing Drive if Bad Sectors Are Confirmed

    If you are running a single-drive NAS (no RAID), you will have no redundancy. Ensure your backup is complete before replacing the drive, as the repair process will format the new disk.

Parts You May Need

NAS-rated hard drive
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Drive tray or caddy
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Uninterruptible Power Supply (UPS)
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NAS-rated hard drive
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Drive tray or caddy
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Uninterruptible Power Supply (UPS)
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NAS-rated hard drive
Check Price on Amazon
Drive tray or caddy
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: your NAS shows multiple drives failing simultaneously, the storage pool is in a 'Crashed' state and cannot be repaired through DSM, you are running a single-drive configuration with no backup and need to recover data from a failing drive, or the RAID rebuild fails partway through. Professional data recovery is expensive but may be the only option if the drive has failed completely and backups do not exist.

Frequently Asked Questions

Will Error Code 27 on my Synology NAS cause me to lose data right away?
Not necessarily right away, but it is a serious warning. Bad sectors mean portions of the drive can no longer reliably store data. If the drive is part of a RAID array with redundancy (RAID 1, RAID 5, SHR, etc.), your data is likely still safe for now. However, bad sectors can spread rapidly, and the drive could fail completely without further warning. Back up your data immediately and replace the affected drive as soon as possible.
Can bad sectors be repaired without replacing the drive?
In some cases, the operating system or a disk utility can 'remap' bad sectors — marking them as unusable so the drive avoids writing to them in the future. DSM's scrubbing tool and S.M.A.R.T. tests attempt this. However, if the Reallocated Sector Count or Pending Sector Count continues to increase after remapping, the drive's health is deteriorating and replacement is the only reliable fix.
How long does it take to rebuild a RAID array after replacing a drive on a Synology NAS?
RAID rebuild time depends on drive capacity and NAS workload. As a rough estimate, expect approximately 8–15 hours per 4 TB of capacity under light load. A 12 TB drive could take 24–48 hours to fully rebuild. Avoid heavy read/write operations during the rebuild to speed up the process and reduce stress on the remaining drives.
What type of replacement drive should I buy for my Synology NAS?
Always use NAS-rated hard drives designed for 24/7 operation and vibration tolerance. Popular options include Western Digital Red Plus or Red Pro, Seagate IronWolf or IronWolf Pro, and Toshiba N300 series. Check Synology's official compatibility list at synology.com/en-global/compatibility to confirm the specific drive model is approved for your NAS model before purchasing.
Why does my Synology NAS keep reporting bad sectors on multiple drives?
If multiple drives are reporting bad sectors, consider these common causes: (1) Drives are old and nearing end of life — NAS drives typically last 3–5 years in continuous operation. (2) The NAS experienced a power surge or sudden power loss — use a UPS (Uninterruptible Power Supply) to protect against this. (3) Operating temperatures are too high — check Storage Manager for drive temperatures (ideally below 45°C) and ensure the NAS has adequate ventilation. (4) The drives are consumer-grade desktop drives not rated for NAS use, which wear out faster under continuous 24/7 loads.

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