Replace a Failing Hard Drive in Your NAS in 2026 Without Data Loss

In this article, we will guide you step-by-step through replacing a faulty hard drive in your Synology or QNAP NAS in 2026. The procedure described here is designed to minimize data loss and ensure quick recovery after replacement. You’ll learn how to identify a failing disk, prepare a new one, swap the disks via DSM or QTS interface, then verify that all your data is safe.

Prerequisites

NAS Synology or QNAP with DSM or QTS operating system installed
A replacement hard drive (e.g., Seagate IronWolf Pro)
Physical access to the NAS to swap the disks
A volume in a redundant RAID level (RAID 1, 5, 6, 10 or SHR): with RAID 0, JBOD or Basic, the data on the failed disk is lost
A recent backup of your important data, made before touching a degraded array

Step-by-step installation

Step 1: Identifying the Faulty Disk

Identify the failing disk by consulting the DSM or QTS interface. You can also, after enabling SSH in Control Panel (DSM) or network settings (QTS), run the following command in an SSH session to see the RAID array status (a ”_” instead of a “U” indicates a missing or failed disk):

cat /proc/mdstat

Step 2: Preparing the New Disk

Purchase a new replacement hard drive compatible with your NAS. Ensure that the new disk has at least the same capacity as the faulty one (ideally the same type and performance).

Step 3: Temporarily Disconnecting the NAS

Temporarily disconnect the NAS to avoid any risk of data loss during the swap. Make sure all critical systems are offline or backed up elsewhere.

Step 4: Physically Replacing the Disk

Shut down your NAS completely, then access the drive bays (front trays on most Synology and QNAP models). Identify the faulty disk from the bay number shown in DSM or QTS (never pull a healthy disk from a degraded array, or you will lose the volume) and gently remove it without forcing. Insert the new disk into the same location.

Step 5: Reactivating the NAS

Power on your NAS and wait for it to fully reboot. Connect to the DSM or QTS interface to verify that the new disk is correctly detected and initialized by the system.

Step 6: Setting Up RAID

Check in your NAS settings (Synology -> Storage Manager / QNAP -> Storage & Snapshots) if the new disk has been automatically integrated into the existing RAID. If not, on Synology open Storage Manager > Storage Pool > Repair, select the new disk and apply; on QNAP, proceed manually with integration following official documentation. Wait for the rebuild to fully complete before doing anything else.

Step 7: Verifying Data Backup

Use DSM or QTS interface verification tools to ensure that all your data has been correctly updated and backed up onto the new disk.

Verification checks

Once all steps are completed, use the following command (over SSH) to check if your NAS is functioning properly:

cat /proc/mdstat

This command shows the status of each RAID array. Once the rebuild is complete, no “recovery” line should appear and each array should show only “U” entries (for example [UU] or [UUUU]). In the interface, the storage pool should be shown as “Healthy” (DSM) or “Ready” (QTS).

Security and best practices

To secure your NAS after disk replacement, ensure that your system has HTTPS activated and a strong password set for the DSM or QTS interface. Also, enable two-factor authentication (2FA) if possible.

Make sure to update all third-party applications and services installed on your NAS regularly. Regularly back up your data to prevent future issues.

Troubleshooting common errors

Symptom: The new disk is not detected by the system. Cause: Hardware issue, faulty drive or improper connection. Fix: Ensure that the new unit is properly connected and test it on another NAS to confirm its condition.

Error: Data Not Synchronized

Symptom: Data is not updated in the new disk. Cause: RAID configuration problem or error during disk replacement. Fix: Manually reset volume synchronization via DSM/QTS interface and wait for the process to complete.

FAQ

The Question? What size of disk should we choose for a replacement?

Answer: Choose capacity equivalent or greater than that of the faulty disk, based on future needs.

The Question? Why does my NAS not recognize the new disk?

Answer: Check physical connections and consult documentation to verify if firmware updates are required.

The Question? Were data lost during the disk swap?

Answer: If you followed this tutorial correctly, your data should be intact and backed up on the new disk.