Mac Says Storage Is Full but Nothing’s There: 7 Real Causes

It’s eleven thirty at night.

You’re trying to export a video, or install an update, or save some tiny file. And up pops the sign: “Your startup disk is almost full.”

Fine. You open Finder. You check Documents: 12 GB. Downloads: 30 GB. Desktop: 4 GB. Photos: 60 GB.

You add it up.

It doesn’t come to even half of what it says is taken.

And then comes the uncomfortable moment, the one where you start thinking that maybe the problem is you, that you forgot something, that there’s a 200 GB folder lost somewhere and you can’t find it.

You didn’t lose it. It’s hidden. Not the same thing.

Look, macOS stores a brutal amount of stuff in places Finder doesn’t show you by default, and on top of that it explains it to you with words that mean nothing. Here are the seven real causes, in the order I run into them most.

1. Local Time Machine snapshots

Number one. By a mile.

Everybody thinks Time Machine only writes to the external drive. It doesn’t. When the external drive isn’t plugged in — which is to say, almost always — macOS keeps snapshots on your own disk and releases them little by little.

This has a lovely side effect: you delete 30 GB, you empty the Trash, and you don’t get back a single byte. Because yesterday’s snapshot is still pointing at those files.

tmutil listlocalsnapshots / in Terminal tells you how many you’ve got. Brace yourself.

2. “Purgeable” space

This one is straight-up a communication problem.

macOS marks certain files as purgeable: it’ll delete them when it needs the room, not before. In the meantime it counts them as used in one place and as free in another.

Result: System Settings says 40 GB free, Finder’s Get Info says 90 GB, and neither one is completely lying.

Restart. Seriously. A very high percentage of “my disk is full for no reason” fixes itself with a restart and ten minutes of patience.

3. Files you deleted that are still open

Almost nobody knows this one, and it’s one of the most maddening.

In Unix, when you delete a file that a process still has open, the file disappears from Finder but the space isn’t freed until that process quits.

You delete a 20 GB log from an app that’s still running. The file doesn’t exist for you anymore. For the disk it’s still sitting there, whole.

Quit the app. Or restart. Same medicine.

4. Your iPhone and iPad backups

~/Library/Application Support/MobileSync/Backup.

In there you can have the backup of an iPhone you sold in 2022, weighing 78 GB, patiently waiting for nothing.

Finder doesn’t show it to you because ~/Library is hidden by Apple’s decision. And nobody deletes what they can’t see.

5. App caches and containers

Every modern app keeps its whole world in ~/Library: Caches, Containers, Group Containers, Application Support.

Spotify with the offline music. Slack with six years of images. Chrome. Figma. The mail client that has downloaded every single attachment since 2019.

Individually they’re folders of 2 or 3 GB. Together they’re half the mystery.

6. Leftovers from apps you don’t even have anymore

You dragged the app to the Trash. You felt great about it.

Its 6 GB support folder is still exactly where it was, under the name of a company you might not even remember, inside a hidden folder, with nothing connecting it to the icon you deleted.

Multiply that by four years of trying out apps.

7. If you code: Xcode, Docker and node_modules

And if on top of everything you’re a developer, this isn’t 7 causes anymore. It’s 7 causes and a black hole.

Xcode’s DerivedData. The iOS simulators, one for every version going back three years. The Docker.raw, which grows and never shrinks on its own even if you delete the images. The node_modules scattered across fourteen projects you finished months ago.

I’ve seen Macs with 180 GB of just this. Not exaggerating, not even a little.

What all seven have in common

Notice the pattern, because it’s the only thing in this whole article that matters:

Not one of the seven is visible in Finder.

It’s not a deleting problem. Everybody knows how to delete. It’s a problem of not being able to look.

And the tools Apple gives you don’t help: a colored bar with one giant gray block called “System Data,” and a list of folders where getting to the fat file means opening triangles by hand, level by level, guessing.

That’s why Hootara shows your disk as a treemap.

Every folder and every file is a rectangle, and the rectangle is as big as what it actually takes up. That 60 GB Docker.raw can’t hide: it takes up 60 GB of your screen. You see it in the first second, without opening anything, without guessing anything, without Terminal.

You click and you go down a level. It tells you what each thing is. And you decide.

One honest heads-up, because I’d rather be the one to give it to you: Hootara is on the Mac App Store, so it runs in a sandbox. The first time, it’ll ask you to grant access to your home folder with a system panel, because without that permission macOS won’t let it read ~/Library. And it doesn’t go into /System, not a chance, and neither should any app you install.

What you see is yours. What gets deleted, you choose.

That’s all.

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Download Hootara on the Mac App Store →

P.S.: if you only do one thing tonight, restart your Mac and check the free space again. If the number changes on its own, it was purgeable and it wasn’t your fault. If it doesn’t change, then yes: there are 100 GB somewhere, and it’s time to go find them with a map.