So with a unique small AppVM, everything is fine but not with a >100G backup? The backup finished without errors with the >100G backup ?You have enough space on your destination?
I had a similar problem (large backup file, but with error at the end) and I choose to break my backup in several chunks to start. You can try to backup the third of your VM, etc. Or backup most of the VM except the big one depending on your setup. (This is only a quick workaround to get backup files).
Are you saving it in dom0 or in another qube? (Or external device?). It could be that you’re saving it in dom0 (the default option) and it has only 20GB of space. What this doesn’t explain is the fact that it finished successfully. So maybe this is not it.
I did a ~400G backup yesterday and it worked fine. So I don’t think it’s because of the size or the Qubes backup utility itself. You should do a new backup like you tried before and take note of the backup name in the directory you selected while the backup is running. When the backup is done, check the directory and see if it’s still there.
Well, don’t know what to tell ya, since personally I’ve never had issues with the regular backup functionality…the only problem I’ve encountered was with backup restore using paranoid mode.
You can try to repeat the process and this time keep an eye on journalctl (in dom0) perhaps?
If possible, please try the backup again, but this time choose (or create) a regular app qube for the backup target, and make the destination just /home/user/. (In other words, don’t attach an external device to the app qube or anything like that, but remember to increase the app qube’s private storage as needed.)
The purpose of this is to separate the act of creating the backup from the act of copying of the data to the external device. If the backup works this time, then you’ll know that the problem is with the copying of the data to the external device, not with the backup itself (or vice versa if the problem persists).