Time Machine: Backups not thinning on external drive

jinet wrote:

I have an external drive, only 2TB, which I use as a remotely stored periodically updated TM backup drive.

It shows this

Official Apple Support Community

But in the finder I see this:

Official Apple Support Community

.

I realize that I am low on storage. But I thought it would thin out earlier backups to make room for new ones. The last backup was from April. But nothing is showing when I go to Browse backups. It shows the same thing: 0 files, 99.99 GB free.

When I Browse Backups, none show apart from those made when I plugged the drive in again yesterday. They must be there (they are taking up the rest of the disk space, invisibly. I just cannot access them

DiskUtility shows no problems with the external disk.

Is there a way to repair this or do I have to wipe the drive and start over?

tx

if there is an issue with that backup you can reformat the drive as new and start a fresh backup sequence and compare your results going forward..

GUID /APFS

Erase and reformat a storage device in Disk Utility on Mac

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

From Finder for a look see—

I can't claim to be able to definitively diagnose and solve your issue here. But I can offer a few observations and suggestions:

All your backup drives show only a small amount of free space, on the order of 100 GB - 200 GB available for backing up. Yet your backups have been operating for between 1 and a few months only, a relatively short time to use up 90% to 95% of the space on those external Time Machine drives, which I assume are 2 TB or more in size.

I have two Time Machine drives and they are 2 TB in size, backing up about 450 GB used on a 1 TB MacBook Pro. They started in 2022 and now have 350 GB free, approximately.

I am guessing maybe you have some very large files that are modified frequently, maybe a virtual machine or some sort of large database? If so, one expects that to more rapidly use up the available space on the Time Machine backups. Time Machine also looks for 2x to 3x the needed space on the destination drive before it starts the next backup, why so conservative I don't know, but perhaps to ensure the drive does not physically fill up, which might make it unusable. So if your next backup requires ~ 40 GB, it might refuse to do the backup.

As others suggested, I would erase/format the problematic drive and start over with it, I would doubt its reliability now as a backup. You might also look to see if there are some very large items being backed up that change. Just logging in to a virtual machine and doing nothing and logging out can result in the entire thing being backed up as it looks "changed" to Time Machine. This is very wasteful and not what Time Machine was optimized for, so consider excluding those large items from Time Machine and instead doing separate clone type backups to a separate drive of just those few large items. Software like CCC and SuperDuper can be configured to do this and to efficiently do incremental updates to such separate clone type backups.

It also appears that at least some of your drives are infrequently used for Time Machine. If many days to ~ weeks go by between backups, the next backup can require ~ tens of GB (or more, depending on how you are using your Mac) which can make this problem (above) more likely to occur.

Launch Disk Utility and run its First Aid routine on the drive and any containers, volumes and partitions it contains.

Repair a storage device in Disk Utility on Mac - Apple Support

What I do is use CarbonCopyCloner for those weekly and monthly backups instead of Time Machine. It is not as finicky about how long the drive is disconnected and doesn't rely on those large snapshots to update when the drive is reconnected.

for CarbonCopyCloner go to > https://bombich.com/

for SuperDuper go to > https://www.shirt-pocket.com/

Plus restoring and/or migrating from a CarbonCopyClone is faster and easier than from a Time Machine backup.

If you never use Time Machine to recover individual files.. Then CCC can easily fulfill the 1-2 portions of your 1-2-3 backup strategy. Just use one connected drive for daily backups and use another that only gets connected for the occasional weekly/monthly backup.

What is the total size of all the data from all the enabled volumes that Time Machine is backing up to this drive?

It is possible that there is too much to complete a successful backup even with thinning.

jinet wrote:

Thanks. I think a clean start is the only way forward. And perhaps I should run it on CCC (which I use for other backup purposes (certain large folders containing music, for example), though this raises a question about the 1-2-3 backup system: is it recommended that two members of this series be in the same backup format, or is it advisable, even preferred, to use different backup software (eg TM, CCC) for two members if the third is cloud-based (as is the case for me: I use Box for my most critical files)?

I agree with den.thed.

Also, if you were to be using Time Machine, I would recommend a second non-Time Machine method (such as CCC or SuperDuper, I have been using SuperDuper for years). The reason being that Time Machine has more complex underpinnings and I could envision a systemic problem on someone's Mac that affects both of the Time Machine drives. Whereas (and I think this is what den.thed was already articulating), a "clone" type backup is simpler in its architecture; unless you exclude some files or folders, it basically clones everything (minus some temporary files) and you can easily inspect the clone to make sure it is indeed a mirror image of the original.

And my experience is that SuperDuper (and no doubt the same can be said for CCC) can be much quicker than Time Machine because Time Machine is checking versions and working with scores of links to enable restoration from multiple (many) points in time in the past. Migrating to a new Mac from a "clone" backup also can be much faster because it doesn't need to work through the logic of the Time Machine architecture.

The downside of a "clone" backup is that it is just one backup from one point in time. But that can be mitigated by doing more than 1 clone backups at different times, or right after a change to important files.

I also value diversity in the tools used for backups. You have Box for cloud storage, which is good; a bug in Time Machine won't affect a SuperDuper backup, and a bug in SuperDuper won't affect a Time Machine backup.