Time Machine backups to NAS fail

A search on macrumors suggests this is a common issue. Any suggestions on how to resolve this?

A NAS has never been a reliable backup solution for Time Machine. It was never supported over AFP, and only recently has Apple listed a NAS as disk you can use with Time Machine (as long as it supports the Time Machine over SMB specification).

You should not use AFP--The AFP implementation on the NAS isn't really AFP and Apple has dropped AFP from its networking. The fact that the instructions suggest using their hacked version of AFP doesn't bode well for its support of the SMB specification.

The NAS must specifically support the Time Machine over SMB specification published by Apple. If your NAS is running Samba ver. 4.8 or later, it should support that, but that may not be true for all NAS. They could be running some modified version.

Backing up to an external disk connected to my Mini has worked flawlessly since Time Machine was available. I have never heard of any success stories using a NAS (except the old, discontinued Time Capsule), but then if they were successful, they wouldn't necessarily post here. The common theme here is if it does backup successfully, when it comes time to restore, it doesn't work.

I understand you are only using SMB. What you don't understand is that is not the same as the "Time Machine over SMB specification." That specification is what the SMB server must provide in order to allow Time Machine to work reliably. It is not merely that you use the SMB networking service. The SMB server on the NAS (likely Samba), must implement the requirements of Apple's "Time Machine over SMB" specification for it to reliably work. If they don't implement that specification, you may still be able to connect over SMB and backup, but it won't be reliable. You are experiencing a reliability problem with that NAS.

You will have no hope of a reliable backup if the SMB server software does not implement the specification. If it does implement that specification, but you are still having problems, you should contact Sinology and ask them why they claim you can use it with Time Machine, but it doesn't work for you.

I didn't say "supports SMB." I said "supports the Time Machine over SMB specification," which is additional features the server must support in order for backups to be error checked. The fact that their instructions still include AFP without any consideration of the OS of the Mac is foreboding.

Like I mentioned, the initial back up was completely fine.

And, that is what happens 99% of the time with a NAS. It's the subsequent backups and restore that fail. The NAS manufacturers have never seemed to be able to handle Time Machine.

Where on that linked page does it specifically note that it supports the "Time Machine over SMB specification?"

It will share on both AFP and SMB. It only "recommends" using SMB, implying it thinks AFP actually works correctly.

If you are using an OS older than Sierra, you are pretty much stuck with their faulty AFP implementation.

The fact that they claim it works and is supported when Apple specifically does not support it is problematic in my mind.