Synology NAS Error Code 18: How to Fix It
Hard 2-24 hours (depending on array rebuild or recovery time) Critical Severity
Verified June 2026
- Error Code
- 18
- Brand
- Synology
- Product Type
- nas
- Severity
- Critical
- DIY Difficulty
- Hard
- Estimated Fix Time
- 2-24 hours (depending on array rebuild or recovery time)
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Tools You'll Need
- Web browser (to access DSM interface)
- Phillips-head screwdriver (for drive bay removal if applicable)
- External USB hard drive or NAS-accessible backup destination
- Replacement NAS-compatible hard drive (same or larger capacity)
- Anti-static wrist strap (recommended when handling drives)
- Network cable (recommended over Wi-Fi for stable DSM access)
How to Fix Error Code 18
-
Do Not Power Off — Back Up Data Immediately
Do NOT perform a full factory reset or re-initialize the volume until you have exhausted all data recovery options. Doing so will permanently erase all data on the volume. -
Check Storage Manager for Drive Health
-
Check the Volume and RAID Status
-
Run a S.M.A.R.T. Extended Test on All Drives
Do not remove or swap drives while the NAS is powered on unless your NAS model explicitly supports hot-swapping. Check your Synology model's documentation first. -
Attempt a Volume Repair (Degraded RAID)
Use a new drive of the same or larger capacity as the original. Never remove a healthy drive from a degraded array — this will crash the volume entirely. -
Run Synology's Built-In File System Check
Do not interrupt the file system check once it has started. Interruption can cause further corruption. -
Check DSM Logs for Detailed Error Information
-
Update DSM Firmware
Only update firmware if the volume is in a stable state. Do not update DSM on a crashed or actively failing volume without consulting Synology support first. -
Use Synology's Data Scrubbing Tool
-
Contact Synology Support or a Data Recovery Service
Do not attempt to open hard drives in a non-cleanroom environment. Physical drive disassembly will void warranties and can permanently destroy remaining data.
Parts You May Need
NAS hard drive
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Drive tray or caddy
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External USB hard drive
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NAS hard drive
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Drive tray or caddy
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External USB hard drive
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NAS hard drive
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Drive tray or caddy
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External USB hard drive
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When to Call a Professional
Call a professional data recovery service immediately if: (1) the volume shows 'Crashed' status and data is not accessible, (2) multiple drives have failed simultaneously, (3) you hear clicking, grinding, or beeping sounds from the NAS drives (signs of physical failure), (4) S.M.A.R.T. tests show severe errors on more than one drive, or (5) you have no recent backup and the data is business-critical or irreplaceable. Synology-authorized service partners and independent RAID recovery labs have specialized tools to recover data from crashed arrays that cannot be repaired through software alone.Frequently Asked Questions
Will I lose all my data with Synology Error Code 18?
Not necessarily. Error Code 18 means the volume has failed, but data loss depends on the root cause. If only one drive has failed in a redundant RAID array (RAID 1, RAID 5, RAID 6, or SHR), your data is likely intact and recoverable by replacing the failed drive and rebuilding the array. If the volume is fully crashed or multiple drives have failed, professional data recovery may still be possible but is not guaranteed. Always maintain a backup — the 3-2-1 rule (3 copies, 2 different media types, 1 offsite) is strongly recommended.
Can I fix Synology Error Code 18 without losing data?
Yes, in many cases. If the error is caused by a single failed drive in a RAID array, you can replace the drive and use Synology's built-in Repair function to rebuild the volume without data loss. If the error is caused by a file system issue, running the built-in fsck (File System Check) can often repair the volume. However, if the volume is fully crashed or the underlying hardware is severely damaged, data loss may be unavoidable without professional recovery services.
How long does a Synology RAID rebuild take after replacing a failed drive?
RAID rebuild time depends on the drive capacity, drive speed, and NAS workload. As a rough estimate, expect approximately 1-3 hours per terabyte of drive capacity. A 4TB drive in a RAID 5 array could take 6-12 hours or more to fully rebuild. During the rebuild, the NAS remains operational but in a degraded state, so avoid heavy usage and do not power off the NAS until the rebuild completes.
What causes Synology Error Code 18?
Error Code 18 is typically caused by one or more of the following: a physically failed or failing hard drive, a degraded RAID array that has lost too many drives to maintain redundancy, a corrupted file system on the volume, sudden power loss during a write operation, or in rare cases, a DSM firmware issue. Drive failure is the most common cause, which is why regular S.M.A.R.T. monitoring and scheduled data scrubbing are important preventive measures.
Should I replace all drives in my Synology NAS after getting Error Code 18?
Not necessarily all drives — only the drive or drives identified as failed or failing by S.M.A.R.T. tests and Storage Manager diagnostics. However, if your drives are several years old (NAS drives typically have a 3-5 year lifespan under constant use), it is wise to proactively replace all drives over time using a staggered replacement approach. Never replace all drives at once, as this will destroy your data. Replace one drive, let the array rebuild completely, then replace the next if needed.