Tuesday, March 19, 2024

Clearing Space on Your Mac

Adam Engst:

Glenn Fleishman recently had to wipe one of his teenagers’ Macs after a massive Steam game download led to stalled Time Machine snapshots, resulting in a Mac with just 41K free. They tried numerous approaches to clearing space, but nothing worked—every attempt to delete files was met with errors complaining about the lack of free space.


Longtime Mac users often get caught up in looking at the amount of free space reported by the Finder. We’ll check the storage numbers shown in a Get Info dialog, delete something, and check again. Don’t waste your time!


Instead of stressing about exact numbers, I want to offer you a set of steps that will clear space quickly and easily on most Macs.

This is good advice. I would add two things:

  1. Removing local copies of iCloud Drive files is not great because then they are no longer backed up. You can do this in a pinch, but I don’t think it’s a good long-term plan.

  2. If you aren’t the type to keep around huge files/folders that you don’t need, I would start with deleting local Time Machine snapshots. For me, at least, they regularly consume hundreds of GB on my internal SSD to store data that I mostly don’t want (huge files that I’ve downloaded and then discarded or offloaded to a spinning hard drive) and/or that is also on my external Time Machine backups. Carefully pruning files is sort of pointless in a world where Time Machine will just use whatever space you free up to store more snapshots. It certainly does not respect the rule of thumb of keeping 10–20% of the drive free.

    However, Engst adds something that I didn’t know but have perhaps seen in action:

    Even though the snapshots are on your startup drive, deleting them seems to prevent the Time Machine interface from showing data that has been copied to your external Time Machine drive. If you need to recover something from the time covered by the snapshots, you may be able to do that by manually browsing each Time Machine backup folder in the Finder.

    I have lately found the Time Machine restore interface almost useless because it can’t show most of the snapshots. Browsing them directly works great, though.


Update (2024-03-21): Nick Heer:

For whatever reason, when iTunes was replaced with Music, MacOS did not remove the now-irrelevant cached Apple Music files from iTunes. Deleting that folder freed up 38 GB of space.

While my photo library is stored on an external disk in Photos, I export selected RAW files to a folder on my local disk and edit those ones in Lightroom. It turns out those files are able to be losslessly compressed through a Lightroom feature called “Update DNG Previews & Metadata”. It is poorly documented and ambiguously named, but running it on my library resulted in a 40% disk space savings — huge, across thousands of photos.

13 Comments RSS · Twitter · Mastodon

I browse Time Machine directly for what I need not because snapshots but because the Time Machine restore UI is so, so, so unbearably slow.

Now I know why people complain about storage space on MacBooks.

I've never had time machine turned on. There has been one single instant when I wished it was on, but then I did some further digging and the issue was solved.

@foobat I wonder if this is an APFS thing? Time Machine browsing definitely seems much slower than it was, say, 10 years ago.

Space management on the Mac is now largely indeterminate thanks to APFS, Time Machine snapshots, purgeable space, and more, as Howard Oakley explains. These technologies render the Finder-reported number unreliable at any given point in time. Even after you empty the Trash, it may take macOS several hours or more to update its free space reports. Restarting may or may not help trigger a recalculation.

I remain in awe that Apple unsolved the largely solved problem of filesystems.

Just use GrandPerspective to find the largest files:

I think it's a good idea to define the default download folder in Safari on an external Thunderbolt SSD and exclude this folder from Time Machine. This saves snapshots on the internal SSD and saves space for the TM backup.

It's important to remember that as long as you have Time Machine set to back up automatically, it will recreate snapshots over the next 24 hours after you delete them. So it's a good technique if you need MORE GIGABYTES NOW but it won't likely make a difference after a day or so.

I included that technique low down in the article because I consider any kind of manual intervention with backup systems to be a philosophically bad idea, whether it's selecting what to backup manually, triggering backups manually, or messing with the system's underpinnings manually. It's all fine and nice until you need your backup, and it's not there because you did something wrong.

@Adam Well, new Time Machine snapshots will use up the space regardless of what you deleted to free up that space. It seems to me that the options are: (1) have so much free space that the full set of Time Machine snapshots still leaves enough real free space, (2) ensure that any large temporary files are saved on another drive so that they don’t get retained by snapshots, (3) manually prune huge snapshots. I see your point about the risks for messing with your backups. On the other hand, I currently have 200 GB of Private Size for snapshots that are a month old, with similar snapshots from around that time also stored on external Time Machine drives. If I need more space those will be the first to go. And my disk usage seems to be spiky enough—with most snapshots having less than 1 GB of Private Size—that I’ll have the free space for a while.

I've given up on understanding free space. I was using ~87% of my 1 TB storage, but *sometimes* when Arq started a backup (creating a snapshot) I'd suddenly lose nearly 100 GB of free space, taking me dangerously close to full. A few minutes after the backup finished usage would go down again (also in a sudden jump), but this was untenable, so I freed another 200 GB.

At first this was effective, but for the past week (matching the upgrade to 14.4) every snapshot has been growing bigger. As I'm writing this, my Mac went from 66% used to 92%.

I can certainly understand snapshots increasing usage, but such sudden jumps should imply I have truly massive files being CoW'd, and I haven't been able to identify anything. Also, it doesn't make sense to me for space to drop after the backup, since Time Machine snapshots linger for 24 hours anyway, and they would have to retain whatever files are causing this behavior.

Yet another area where either Target Disk Mode or removable disk drives can save your bacon. Yes, you need another Mac, and maybe another drive, but it is generally be possible to repair this situation tactically with TDM.

We still have TDM, but I miss removable drives. My son's Mac recently had its logic board die and we had no way to get any data off the machine. Fortunately, Arq backups were enabled and running so there was no data loss, but I was *extremely* worried until we confirmed the Arq backups were good.

With data recovery, it always feels better to have a belt and suspenders approach.

Just shooting from the hip here, but why does Apple not simply remove the drive properties from Finder since it's largely, perhaps completely useless? The settings drive interface should provide a better breakdown (not that I know first hand if it's any good these days either). Is is ridiculous Apple can't report free space correctly? Yes, of course it is. I checked my daughter's Windows 10 laptop and the file manager could do that just fine and Thunar on my Linux laptop likewise handles this perfectly well. But you know, Apple has never seen a problem it couldn't over engineer its way into…

Also, as a person who assiduously avoided Time Machine during his time as a Mac users, would Carbon Copy Cloner still provide a better experience with backup? All the years of random problems with Time Machine were adroitly sidestepped by using CCC, and before that SuperDuper! Any current users able to report back if you simply disable Time Machine and use a third party app, does it help with free drive space issues?

@Nathan CCC is great. It also creates APFS snapshots, so it can cause the same problems as Time Machine, but it offers more controls over how many to keep and how much free space to require.

@Michael Tsai
Thank you for clarifying. Sounds like there is still some benefit to using CCC over Time Machine even if the file system snapshots are still a component of the backup. Very interesting. I'll let my dad know. I got him on CCC years ago because I liked it better than Time Machine. I can't remember if he's still using it for backup.

Leave a Comment