Delayed Write Failure in a NAS

I have resolved problems with "delayed write failure" errors for my NAS device.

Processes such as backups and file copies failed after running normally for fifteen minutes or more. The messages displayed by the failing process were not helpful. I found the "delayed write failure" messages in the event logs displayed by the Windows Event Viewer.

I tried fixes that included ...

• Enabling and disabling "jumbo frames" in the NAS network adapter. Problems occurred when jumbo frames were both enabled and disabled.
• Enabling and disabling "checksum offload" and "large send offload" in the network adapter driver settings made no difference.
• Enabling and disabling opportunistic locking by setting "OplocksDisabled" in the "mrxsmb" key in the registry made no difference.

Initially, I did not like the look of the network cable that was supplied with the NAS and tried a cable of my own but this CAT5 cable would only allow the NAS to operate at 100 Mbps. The cable supplied with the NAS allowed a connection at 1000 Mbps. Initial success with the supplied cable caught me out.

I eventually swapped the network cable in attempt to prove that the fault was with the NAS unit and not the network. To my surprise, changing to my own CAT6 cable fixed the problem.

A complaint to the manufacturer of the NAS, the supplier of the dodgy cable, brought a response that the cable was supplied for use during NAS setup and was not intended for long term use. This is silly ... supply a cable that always works or do not supply a cable at all.

I should have remembered that the solution is often simple and obvious ... one fix for delayed write failures in a NAS is a good network cable.