How to limit Time Machine storage usage?

[hehe299792458]

I am using a Synology NAS with about 20TB of storage that I use for both TimeMachine backups as well as other storage needs. But I'm having trouble limiting the amount of storage TimeMachine uses. It just uses ever more storage until it's all full, and then macOS gives me an error message saying there isn't any more space.

As far as I understand, TimeMachine should delete old backups when space runs out. So why isn't it doing that?

 

[apostolosdt]

[…] As far as I understand, TimeMachine should delete old backups when space runs out. So why isn't it doing that? View attachment 2357116

It does, and one way to make TM use less space is to switch it to manually backup mode.

 

[hehe299792458]

It does, and one way to make TM use less space is to switch it to manually backup mode.

TimeMachine doesn't delete old backups if it's on an automatic schedule (e.g backup once an hour)?

 

[apostolosdt]

TimeMachine doesn't delete old backups if it's on an automatic schedule (e.g backup once an hour)?

TM deletes oldest backups irrespective of which mode, auto or manual, it runs. Each user follows a plan; mine is this:
1. TM drive is at least 4x the internal SSD.
2. Internal drive keeps only the OS and apps; all personal data and files are on the Cloud.
3. Photo gallery is too large to be on the cloud or in the internal SSD. I keep it in an an external drive and clone the latter twice.
4. I manually run the TM only after a critical installation and always after an OS update.
But that’s only fits me, not everyone I guess.

 

[FreakinEurekan]

The reason you’re seeing that message is that you don’t have enough drive space for the data being backed up. Time Machine will “prune” older backups but it isn’t prime an hourly backup for 24 hours or a daily backup for 1 week, etc - and you don’t have backups eligible for pruning.

Typically this means you have either too small a backup disk (bare minimum would be 2X your total data size, 3X or 4X is better) - or, you have large data files changing frequently. If you’re editing video, for example, be sure your “scratch” folder is excluded from Time Machine. If you use VMs, exclude the VM files (use the client OS to back up that data, since it can be a lot more efficient than backing up a multi-terabyte VM image due to a minor change.) These are just examples; each person needs to examine their own data usage & exclude folders with large, frequent data changes if the data isn’t critical in the event of loss.