Why isn't Time Machine pruning backups?

born2boot wrote:

• The 486 GB is the total size of the backup set for my MacBook Pro. That is, everything except what i have excluded from the backup.

It appears that Time Machine's philosophy is keep everything forever, including deleted files. The implication of Time Machine not pruning versions or deleted items is that Time Machine backup volume will continuously grow, never reclaiming any space for older or deleted items I have no interest in retaining.

Time Machine volumes want to keep at least one copy of all files around, and wants to prune the oldest files first, which in aggregate means you need enough free storage for that to happen.

The arrival of big files tends to be a problem for marginal-free-storage configurations.

It’s the marginal size for your churn that’s causing the issue here.

A backup solution I have used in the past allowed configuring:

how many versions of a file should be retained

• the oldest age of a file to be retained

• how long to retain deleted files

• deletion of files removed from the backup set (remove files that are excluded)

If you want control over your backups, Time Machine is not your choice.

I can read that 486 GB reference in two ways, either as the size of the current hunk getting backed up, or as 486 GB used from some 512 GB or larger storage device. The former is a problem, as big backup churn isn’t what Time Machine works well with. The latter is “merely” a relatively small HDD for a 512 GB (total) Mac.

TM also gets in trouble when several big files get churned with full-ish and small-ish TM storage, as TM really wants to keep some old copies of all files around.

I’m running 4 to 6 TB direct-attached HDD storage and larger NAS HDD configurations for Time Machine.

That size range HDDs both because of the covered storage capacity, and because the price difference between that capacity range and smaller HDDs was negligible—that was the knee in the pricing and capacity curve when those HDDs were purchased—and as having sufficient free storage means TM doesn’t get hindered by the usual Xcode installer churn.

The three major options here are keeping the HDD connected continuously, or getting a bigger HDD, or to (bigger) NAS (with TM server support). Adding a second and larger HDD is also workable, while the smaller HDD sorts itself, as TM is perfectly happy to run its output to parallel storage archives.

NAS (with TM server support) works well for a MacBook Pro and other laptops, as that gets used whenever the Mac is connected to the same Wi-Fi, and not just when the external TM storage is physically connected to the laptop. But NAS (with TM server support) is also obviously more expensive than direct-attached HDDs, too.

Never manually attempt to remove Time Machine content. Ever.

Time Machine consolidates daily backups into weekly backups, and those into Monthly backups and it will prune backups when it is ready. It doesn't just blithely remove as much space as you think you need in order to complete a current backup. So yes, you may be in the market for a new Time Machine drive with larger capacity to meet your backup needs.

As long as my Mac is powered during the day, Time Machine backups are completing every hour. If you were doing this, you wouldn't be faced with gargantuan backups (e.g. 486 GB) and run into a storage crunch on the current TM drive.

This 1.3 TB HDD isn’t worth the effort of this thread.

I wish you and your data well here, with whatever resolution you might decide to use.