Synology NAS Error Code 23: How to Fix It

Q: Will I lose my data when Synology shows Error Code 23 (RAID degraded)?

Not necessarily. In most RAID configurations (RAID 1, RAID 5, SHR, SHR-2), your data remains accessible even with one failed drive because redundancy is built in. However, you have zero fault tolerance in this state — if a second drive fails before you rebuild the array, you could lose everything. Back up your data immediately and replace the failed drive as soon as possible.

Q: How long does a Synology RAID rebuild take after replacing a drive?

RAID rebuild time depends on the capacity of your drives and the workload on your NAS. As a rough estimate, expect about 1 hour per 1 TB of drive capacity under light load. A 4 TB drive might take 4–8 hours, while an 8 TB drive could take 12–24 hours or longer. You can monitor the exact progress percentage in DSM Storage Manager. Avoid running intensive tasks on the NAS during the rebuild to speed it up.

Q: Can I use any replacement hard drive to fix a Synology RAID degraded error?

Synology strongly recommends using drives from their official Hardware Compatibility List (compatible.synology.com). Using an incompatible or untested drive may cause stability issues. The replacement drive must be at least as large as the failed drive — you cannot use a smaller drive. For RAID 5 or SHR arrays, all drives must meet the minimum capacity of the smallest drive in the array.

Q: What is the difference between a degraded RAID and a crashed RAID on Synology?

A degraded RAID (Error Code 23) means the array has lost some redundancy due to one drive failing, but your data is still accessible. A crashed RAID means the array has lost enough drives that data can no longer be read — this is a critical emergency. Degraded arrays can typically be repaired by replacing the failed drive. Crashed arrays often require professional data recovery services.

Q: How can I prevent Synology RAID degraded errors in the future?

There are several proactive steps: (1) Enable automated S.M.A.R.T. tests in DSM to catch failing drives early, (2) Set up email or push notifications so DSM alerts you the moment a drive issue is detected, (3) Use DSM's Scrubbing feature (Storage Manager > Scrubbing) monthly to detect and fix data inconsistencies before they grow, (4) Replace drives that are 4–5 years old as a precaution, and (5) Always maintain a separate backup using Synology Hyper Backup or another solution — RAID is not a substitute for backups.

Abstract

Synology NAS Error Code 23 indicates that your DSM RAID array is in a degraded state, meaning one or more drives in the array have failed or gone offline, reducing redundancy and putting your data at risk. While your NAS may still be accessible and your data intact, you should act quickly because a second drive failure at this point could result in complete data loss. This guide walks you through diagnosing the failed drive, replacing it if necessary, and rebuilding your RAID array to restore full protection.