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???

 

[MajorFubar]

I'd be lying if I said I knew. But to give you some confidence that it has indeed worked , delete something unimportant and check if you can restore it from the time machine backup.

 

[adrianlondon]

I'd be lying if I said I knew. But to give you some confidence that it has indeed worked , delete something unimportant and check if you can restore it from the time machine backup.

Just rename the file; no need to delete something.

 

[wonderings]

Personally I would go with a new drive. I have had a few hard drive issues with Time Machine backups in the past and in the end always had to replace them. Time Machine is great for a daily working backup. To be really safe I also use off site cloud backup through BackBlaze. It is as simple as Time Machine but in the cloud with no size limits which means you can backup external hard drives as well. This is the safest solution for backup, Time Machine and an offsite backup. Back Blaze is around $100CDN a year, give or take a few bucks.

 

[Brian33]

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???

There is a logical explanation, but it involves understanding APFS snapshots, and how Time Machine uses them, and what exactly you "deleted".

Each Time Machine backup after the first exists as an APFS snapshot on the backup volume. TM only copies filesystem objects that have changed since the previous backup. (Actually, I think that only the changed portions of files are copied, at least in many cases, but that's not important here.) Some would say TM always does an "incremental backup" after the first. However, every "backup" looks and acts like a "full backup" when that particular backup snapshot is mounted and traversed with Finder or Terminal commands, or for a restore operation.

In your first paragraph quoted above, you "deleted everything," but don't say how you accomplished this. I think you deleted every APFS snapshot, but you didn't erase all data on the drive (the data that exists outside of any APFS snapshot). I think the TM interface only allows deleting of backup snapshots, and doing so doesn't format the disk. If I'm correct, this still leaves the 81.2 GB of data on the disk.

So, the "first backup" data was still on the disk, but there were no backup snapshots. (Not sure what this would look like in the TM interface -- probably it looks like having no backups.) Then when you started a TM backup, TM only had to copy data that was different from what was (still) on the backup volume. This action created the first backup snapshot (again, which LOOKS like a whole 81.2GB of data) and would be very quick. It only had to copy the differences between your boot drive and the data (still) on the backup disk.

Then in the last quoted paragraph, you "erased" the drive (with Disk Utility?), removing not only any snapshots but also the data not in a snapshot. That backup "took a while and again ended up with 81.2 GB." This time, 81GB was actually copied and the duration was noticeable.

So hopefully this is an explanation of "how, when I had deleted the file before [first paragraph time], did it also end up with 81.2 GB and did so in a few seconds???"

If I understand the situation, I'd say you have a good backup and can continue building on it.

 

[Brian33]

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.

As I mentioned above, TM effectively does "incremental" backups, but when you mount a backup snapshot it looks and acts as a full backup. There is no way to change this behavior of Time Machine.

 

[mac_in_tosh]

In your first paragraph quoted above, you "deleted everything," but don't say how you accomplished this. I think you deleted every APFS snapshot, but you didn't erase all data on the drive (the data that exists outside of any APFS snapshot).

I deleted every folder on the drive.