Time Machine backups using a NAS fail every few months…why?

Is the Synology version current, and is the Time Machine path using thenTime Machine server support?

if this was also happening with Time Capsule, I’d wonder if the local Wi-Fi or wired network is glitching.

The Synology NAS devices have never been reliable with Time Machine. I gave up on them a long time ago and suggest you do the same.

Yes it is a common problem. After weeks of tedious troubleshooting Synology never identified the reason; they only blamed everything else. Mostly Apple. I concluded they were incompetent or disinterested or both but I wasn't about to trust my backups to them.

Why did you stop using the Time Capsule? All of mine have been 100% reliable. If yours has a failed hard disk drive they can be replaced (with difficulty).

I’m just about ready to simply start backing up to multiple attached drives and stop using the NAS altogether.

That's a good idea.

Concerns about hard disk drive longevity are justified since nothing lasts forever. One should never rely upon one and only one device for backups, but you can connect any number of external, cheap, disposable hard disk drives to a TC and add them to TM. When one fails throw it out.

For that reason, be sure to choose encryption when adding any device to TM. Otherwise that backup can be used to effectively create a duplicate of the Mac it backs up... assuming the failed hard disk drive itself can be revived long enough to work for at least a little while. Most of the time, they can.

More than one external HDD should use a powered USB hub due to the power limitations of the TC's USB port. And if you are so inclined, you can replace a TC's internal hard disk drive. Your 3 TB version is one of the more attractive options since Apple never made a TC with a capacity greater than that, but there is no limitation to its capacity or that of any external USB hard disks.

Are there other NAS devices that have a solid track record with Time Machine?

I wish there were. There is at least one experienced participant on this site who has reported good success with the Synology NAS, but in the end it's your data and no one other than you can decide upon the best backup strategy for your particular needs. Personally I don't trust anything until I verify its ability to reliably back up and restore, and the only NAS device that has been able to do that with Time Machine is the Time Capsule.

In the case of your wife's Mac I completely understand, and that's why I use TCs (or, the latest production "tall" AEBS with external hard disk drives). Nothing else is as reliable or as maintenance-free. Turn it on and forget about it.

It is my understanding that Carbon Copy Cloner can be used with non-Apple NAS devices, but I no longer use CCC myself so I can't personally verify that. When I did use CCC I found it to be an excellent program though.

Having said that you don't really need to connect an external hard disk drive other than occasionally. Once every few days is ok because every Mac that uses TM creates "local snapshots" that are completely restorable full system backups. They are flushed to the external TM backup drive whenever it becomes available. TM will begin to complain after ten days have elapsed without the opportunity to do that.

The obvious limitation of "local snapshots" is that they cannot be used to restore a Mac in the event it becomes lost, stolen, or unbootable.

... my laptop shows 17 other networks available to connect to!

That certainly qualifies as a challenging wireless environment, and whatever you see in that interface doesn't even reveal the existence of "hidden networks" that can also contribute to wireless interference. If you want to use the TC or even a non-Apple NAS, you can minimize that uncertainty by connecting it to your wireless router with an Ethernet cable. Should you decide to use the TC again you will need to start with a "hard reset" otherwise it will insist upon using its previous connection method. The "hard reset" will have no effect on any existing backups.

This isn’t the NAS.

Synology here has been solid.

This is 17+ uncoordinated Wi-Fi networks, and the perpetual cascading channel reassignments. In Wi-Fi dense areas, rolling pileups arise when the individual uncoordinated Wi-Fi networks try to adapt to the ubiquitous din.

For access points, you’ll want to be running at least Wi-Fi 6E, and with denser (and lower power) coverage. Preferably with wired backhaul and not Wi-Fi or mesh backhaul, but newer mesh might be workable. You’ll want more access points and at lower power.

Shut off 2.4 GHz, and shut off 5 GHz if your client gear is new enough.

Maybe run a second SSID for IoT gear in 2.4 Ghz and 5 Ghz, if that’s needed. Use WPA2/WPA3 transitional. Keep your important gear off that.

WPA3 and stay in 6 GHz where you can, use 5 GHz with narrower channels where you must, and stay entirely out of 2.4 GHz with your core Wi-Fi clients.

As a test of what I’m predicting above, shut off 2.4 GHz, select narrower 5 Ghz channels, and see if things become (somewhat) more stable. Run a scan with WiFi Explorer app or similar tooling, too. If you see “mountain ranges” everywhere in the local Wi-Fi activity plots and particularly in the 2.4 Ghz band as I’d expect with 17+ networks, you’re going to have bad experiences with heavy network transfers.

PS: I’ve had TC around, but that stuff started having unreported and unexplained ~10 second signal drop-outs. I’m supporting a few TCs that are still used as NAS devices. But those same TCs were (also) flaky whenever the Wi-Fi was flaky, as heavy network data transfers (read: backups, restores) get wobbly. That formerly-Apple Wi-Fi network got replaced with Ubiquiti gear, too.

I replaced the disc in one of my Time Capsules (the tall one) last year. It was fairly easy, especially since I'm considered a bit clumsy, and I wouldn't hesitate to do it again. The hardest bit was cutting the rubber mounts to fit the new disc corners and then getting them to slide and seat again - but a bit of glue and WD40 helped. They have a reputation for the PSU failing but so far so good. I've got two units as spares plus one of the flat ones somewhere.

I use a QNAP 4-bay NAS and I haven't had any problems at all with TM backups. I also do a plain backup of files and photos to the NAS using Backuplist+, which is an rsync GUI but I believe it can clone too.

The number of competing wireless networks is likely to be a contributing factor, but I had the complimentary experience: none of my locations have any competing wireless networks. Not a single one. None that are not a short drive or a long walk away.

That had been one of the factors Synology wanted to blame, but when I provided the output of Wireless Diagnostics to them (among other copious and time-consuming troubleshooting information) they proceeded to blame everything else, ad nauseam.

In the end I concluded Synology was either unmotivated or unable to keep up with changes in Time Machine, which Apple almost never publicly revealed even years ago. I happen to know of bugs that were never acknowledged, but were quietly (and quickly) fixed. Documentation has always been sparse to nonexistent.

... that stuff started having unreported and unexplained ~10 second signal drop-outs.

I can't explain that either. Needless to say that hasn't been my experience, and I wouldn't tolerate it if it were.

If I had to migrate my network installations away from Apple devices Ubiquiti would be at the top of the list.

Good to know. I'm eager to upgrade their HDDs to 6 TB capacities but I'm in no rush for anything to fail. Eventual PSU failures could be fatal, unless they are repairable on a component level and I haven't delved into that.

John Galt wrote:

Good to know. I'm eager to upgrade their HDDs to 6 TB capacities but I'm in no rush for anything to fail. Eventual PSU failures could be fatal, unless they are repairable on a component level and I haven't delved into that.

I used the iFixit instructions. Fine tweezers and good eyesight needed for the connectors. The rubber mounts were a pain, although if the Capsule is just going to be sitting on a shelf and not transported anywhere then it's less important to get them to fit perfectly - just good enough to close the lid.