Time Machine Backup Failed

[mac_in_tosh]

I use an external SSD to periodically run Time Machine. Today I got a "Backup Failed" error message. There's plenty of space available on the drive. I ran Disk Utility to do First Aid. I ran it on all three items (Samsung Portable SSD T5 Media, Container disk3 and Time Machine Backup). The first and last items were okay but for the middle one it said operation failed:

Checking storage system and repairing if necessary and if possible
Performing fsck_apfs -y -x /dev/disk2s2
error: container /dev/rdisk3 is mounted.
Storage system check exit code is 65.
Storage system verify or repair failed. : (-69716)

What does this mean? Should I just erase the drive and start all over?

Thanks.

 

[mac_in_tosh]

Waiting for a reply I found a suggestion online to remove and re-add the Time Machine backup destination, which I did. Re-trying Time Machine twice it seemed to go real fast without an error but checking the size of the files created they were very small, the largest being only about 30 MB. I noticed, however, that it also showed another file ~6 GB file created this morning, when I was getting all the error messages, as well as an even larger file from a couple of months ago that corresponds to when I first started using this particular SSD drive.

Does that mean that this morning's backup actually worked?

Also, is Time Machine set up to only do incremental or differential backups? Which is preferable and how would I change this? I can't find any option in System Settings in Sequoia 15.5.

 

[Fishrrman]

I can't help with the tm backup. I've never used tm.

But I CAN suggest that you try either CarbonCopyCloner or SuperDuper.
Better yet, try BOTH of them (use a spare SSD).
Both are free to download and use. CCC for 30 days. SD will do a "full" backup forever without having to register it -- to do incremental backups, you need to register.

 

[MajorFubar]

I might be wrong but based on the file sizes I've seen I think TM does incremental backups.
I have it running constantly on my 2TB Mac Studio, connected to a 4TB hard drive.
The reason I use it in preference to third-party apps is the ease by which I can reach back within MacOS and find files (or folders) or versions of files (or folders) that I changed or deleted months ago. Inevitably it's a bit more clunky with third party apps because they lack system-integration, obviously.

I'd say your backup was successful.

 

[mac_in_tosh]

I'd say your backup was successful.

Thanks. However I'm still getting that "operation failed" message for Disk Utility check of Container disk3. I have no idea what Container disk3 is.

So I decided to be brave and deleted everything from the external drive and start over with a Time Machine backup. It went very fast, about 10 seconds, which didn't seem right. But when I used Get Info to check the size, the top folder on the drive is 147 KB and the data file inside is 81.2 GB.

How could it have done 81.2 GB so fast?

Edit: I went further and erased the drive, then encrypted it as I had done before. I then set it as the Time Machine backup destination (oddly enough it did its own encryption and I used the same password) and started all over again. It took a while and again ended up with 81.2 GB. I'm confident in this backup, but how, when I had deleted the file before, did it also end up with 81.2 GB and did so in a few seconds???