Synology NAS Error Code 34: How to Fix It

Q: Will I lose my data when Synology Error Code 34 appears?

Error Code 34 itself means the expansion unit is disconnected — your data on those drives is not immediately lost. However, if drives in the expansion unit are part of a storage pool, that pool may become degraded or inaccessible until the connection is restored. Reconnecting the expansion unit properly should allow DSM to remount the pool without data loss. Avoid writing to or modifying the storage pool until the connection is stable again.

Q: What expansion units are compatible with Synology NAS devices?

Synology offers DX (desktop expansion) and RX (rackmount expansion) series units that are compatible with specific NAS models. You can check the official Synology Compatibility List at synology.com/compatibility to verify which expansion units work with your specific NAS model and DSM version. Using an unsupported or unlisted expansion unit can cause connection errors including Error Code 34.

Q: Can a bad eSATA cable cause Synology Error Code 34?

Yes. A damaged, loose, or low-quality eSATA or proprietary expansion cable is one of the most common causes of Error Code 34. The cable carries both data and control signals between the NAS and expansion unit, so any degradation in the cable can cause the expansion unit to appear disconnected. Replacing the cable with a Synology-recommended or high-quality cable often resolves the issue.

Q: How do I prevent Synology Error Code 34 from happening again?

To prevent recurrence, keep both DSM and your expansion unit firmware up to date, ensure all cables are firmly seated and protected from physical stress, use a UPS to prevent power fluctuations from causing abrupt disconnections, and periodically check Storage Manager for health warnings. Placing both units on a stable surface where cables won't be accidentally disturbed also helps maintain a reliable connection.

Q: Does Synology Error Code 34 mean my expansion unit is broken?

Not necessarily. Error Code 34 indicates a disconnection event, which is most often caused by a loose cable or a power interruption rather than a failed expansion unit. Only after replacing the cable, power cycling both devices, and updating firmware — and still seeing the error — should you suspect a hardware failure in the expansion unit or the NAS expansion port itself. Testing the unit on a second compatible NAS helps isolate whether the expansion unit hardware is the root cause.

Abstract

Synology NAS Error Code 34 indicates that DSM has detected a disconnection from an attached expansion unit (such as a DX or RX series expansion chassis). This can happen due to a loose or faulty expansion cable, a power issue with the expansion unit, or a software/firmware mismatch between the NAS and the expansion device. Addressing this promptly is important because any drives housed in the expansion unit may become inaccessible until the connection is restored.