I have been bitten by Time Machine in the past. There is not much more frustrating than a fried computer and a backup that doesn't work and can't be recovered.

Since then I only use Carbon Copy Cloner [0]. It has very very very excellent documentation and it is well the worth the purchase. The documentation covers lots of backup scenarios, how to do recovery and dealing with error cases. It also lets you create bootable backups on external drives, though I have only used it for backups over the network.

I'm not affiliated, but I can't praise their work enough.

[0] https://bombich.com/

Thanks, but I wanted to understand what the actual problems of Time Machine are, especially with Catalina, and - most importantly - which are the symptoms I should be wary of.

Well one problem I ran into was because of the changes to iTunes audiobooks are now stored in the Books app but the Books app doesn't support external drives for media so the Catalina update includes hours of copying files from my external HDD to my primary Macintosh HD - filling it up almost entirely (I have/had about 300GB of audiobooks) - this was bad enough (as their was no UI telling me it was doing this) but then Time Machine kicked in trying to back up these files (I had excluded the external drive but obviously not the primary partition) but because I ran out of space during the initial Catalina upgrade run, their were lots of artifacts which also got added to Time Machine. Time machine itself started trashing for hours.

I lost probably a day (to a day and a half tidying things up and cleaning up stuff that was not my fault) and of course I have no decent way of managing audiobooks now.

Apologies, I haven't heard of anything and I haven't dared upgrade yet either. Good luck!

For backups, you can simply use rsync. No reason for proprietary solutions when rock-solid opensource alternatives exist.

Yeah, no. CCC goes way above and beyond. Creating verifiable, bootable copies, being able to bundle tasks together, creating recovery volumes, being able to backup locally, remotely or to images etc etc.

Rsync is a good tool but CCC gives massive quality of life. Some of that won’t even be possible with rsync. And rest would require building a complicated set of scripts. Paying Bombich, to deal with all the headaches and mac os shenanigans, $50 every couple of years is a much better deal.

And its not a lock-in like other backup tools. You can access specific files inside the backup without CCC.

CCC + Arq cover all my bases when it comes to backup and restore.

In my own case, TM lost the ability to make new backups to an USB-connected HD. It doesn't report errors. It doesn't explain. Trying to find something useful in Console is a PITA. The only visible symptom is that a few minutes after each backup starts, it ends without copying all that it promised at the start of the process.

I suspect the root cause is some 3rd party software interaction. But since the 3rd party software I have is installed and required by my employer, it's hard to do an A/B comparison.

i had the same problem which was fixed by having more free space on my local drive.

I need + 15 gb free for TM swap stuff.

Apple is notorious for not giving ANY feedback so i only found out after sesrching for a long time on google.

Apple please stop silently failing without messages.

Thanks a lot for your contribution. You write:

"The only visible symptom is that a few minutes after each backup starts, it ends without copying all that it promised at the start of the process."

So you mean it ends "too quickly"? How can you tell if it missed some files?

A significant portion of my hard drive has been completely eaten up by old backups that I can’t seem to remove. I have tried every solution that google provides, there doesn’t seem to be a way to erase these old backups without doing a factory reset.

A bit late on the reply, but here are a couple of places to look – "Time Machine and Backing Up in Catalina". [1] Also see mjtsai.com for Time Machine related posts on Catalina.

[1]: https://eclecticlight.co/2019/11/11/time-machine-and-backing...

I've lost my backup twice. OS says I have to redo the full backup because there's something wrong with it. I have a Time Capsule.

That wasn't introduced by Catalina though, it has been there since forever.

For what I understood it happens when the macbook is forced to go to sleep/loses connectivity while in the middle of a backup. It doesn't cleanly unmount the remote file system and it causes data corruption.

There are some ways of "restoring" the remote FS but they may or may not work, are very slow, opaque (what actually was fixed?) and flaky.

I just switched to an external USB drive for Time Machine and not looking back

If I understand this correctly it corrupted an already existing on-going Time Machine backup so that you had to start just as if you had bought the Time Capsule? And this was made explicit by an OS error at the end (or at the start) of a backup operation?

If TM detects an I/O error while writing to a networked backup volume, it aborts the backup and forces a filesystem check on the remote disk image at the start of the next backup. This fails, because the filesystem actually is corrupt and has been for some time. You had no idea, of course, because TM only reports four-horsemen level errors in the UI, and silently eats the rest. You even had a good run of "successful" backups afterwards, so long as you managed to avoid changing any files in directories with damaged metadata in your backup.

Anyway, as your digital life flashes before your eyes, TM helpfully offers to delete all your backups and start with a fresh disk image now, or delete all your backups and start with a fresh disk image later. And you can't blame it, really, because the filesystem has had some unknown, nonzero amount of corruption for an unknown, nonzero amount of time. For all anyone knows or can prove, the whole backup is random garbage.

This fractal of failure is specific to backups over WiFi. Backups to USB-connected disks aren't that reliable either, because HFS+, but USB backups have all the nines of reliability compared to network backups.