Guides · August 2026

What "System Data" actually is.

You open Storage settings, and a grey bar labelled System Data is eating 150 GB. There is nothing to click, no list of files, and no obvious way to make it smaller. System Data is not a real category. It is the leftovers bin: everything macOS could not confidently sort into Applications, Documents, Photos, Music, or Mail. Here is what is actually in there, what is safe to remove, and what to leave alone.

01 It is a leftovers bin, not a thing

Open System Settings → General → Storage and macOS shows you a bar divided into categories. Most of them mean what they say. System Data does not. It is the remainder: total used space minus everything the categoriser recognised. That is why it has no file list and no "manage" button, and why it grows for reasons that seem unrelated to anything you did.

Before macOS Ventura this same bucket was called Other. The name changed; the contents did not. If you are following an older guide that talks about clearing Other storage, it is talking about this.

On a healthy Mac, System Data sitting somewhere between 10 GB and 50 GB is completely normal. It is worth investigating when it is large enough to hurt, or when it keeps climbing and never comes back down.

02 What is inside it

Roughly in order of how much space they tend to take:

Local Time Machine snapshots. Point-in-time copies of your volume stored on the same internal disk, taken several times a day. These are the single biggest contributor on most Macs, and they can hold tens of gigabytes.
Caches. ~/Library/Caches and /Library/Caches. Browsers, Spotify, Xcode, Adobe apps, and Slack all park data here. It rebuilds itself if you delete it.
Application support data. ~/Library/Application Support. Not caches, this is real app data: mail archives, virtual machine images, game installs that live outside the app bundle, iOS device backups.
Swap and virtual memory. /private/var/vm. macOS manages this and it shrinks on its own.
Logs. /var/log and ~/Library/Logs. Usually small, occasionally enormous if something is misbehaving in a loop.
Downloaded installers and disk images. macOS updates that were fetched but not installed, plus stray .dmg files.
Fonts, plugins, and system extensions. Small, but they land here because they are not documents.

The one that surprises people. iOS and iPadOS device backups made through Finder live in ~/Library/Application Support/MobileSync/Backup and count as System Data. Two old phone backups can be 200 GB on their own, and nothing in Storage settings tells you they exist.

03 Start with snapshots

If System Data is unusually large, check snapshots first. It is the fastest win and it needs no third-party software. In Terminal:

List them: tmutil listlocalsnapshots / prints every local snapshot on the startup volume, named by timestamp.
Thin them: tmutil thinlocalsnapshots / 50000000000 4 asks macOS to free roughly 50 GB by removing the oldest ones, at the most urgent priority.
Check what changed: df -h / before and after, so you can see the actual result rather than trusting the Storage bar to refresh.

Snapshots are not a bug and you do want some of them, since they are what lets you enter Time Machine when your backup drive is not connected. But they are the answer to "where did 60 GB go" far more often than anything in your home folder. There is more on why they hide from you in our guide to a disk that is full while Finder shows free space.

04 What is safe to delete, and what is not

Most advice on this topic tells you to empty ~/Library/Caches and stops there. That is fine as far as it goes, but it is worth knowing the difference between the folders.

Safe: anything in ~/Library/Caches. Quit the app first, delete the subfolder, and it rebuilds. Old iOS backups in MobileSync/Backup, if you have the device or an iCloud backup. Downloaded installers you already ran.
Safe but slow to recover: Xcode DerivedData, simulator runtimes, Docker images, npm and Homebrew caches. All rebuild themselves, but the next build will take a while. We wrote a separate guide on clearing developer caches.
Leave alone: anything in /System, the /private/var/vm swap files, and ~/Library/Application Support folders belonging to apps you still use. Deleting Application Support is how people lose mail archives and app licences.

And a general point: do not run a "cleaner" app that promises to remove System Data for you. The category is a remainder, not a folder, so anything claiming to clean it is really just deleting caches you could delete yourself, usually for a subscription. Our note on that goes into it.

05 Seeing it instead of guessing

Storage settings will not show you what is in System Data, which is the whole frustration. The way out is to stop reading the category and look at the filesystem: map the disk, sort by size, and the mystery resolves itself into named folders you can make decisions about.

That is what we built Delve for. It draws every folder on the volume as a rectangle sized by the space it really occupies, so the 200 GB of forgotten iOS backups or the 60 GB Application Support folder is simply the biggest box on screen. It counts APFS clones and hardlinks once rather than once per copy, and it marks iCloud placeholder files so a 4 GB stub does not pretend to be 4 GB of local storage. The number it shows you is the number you get back.

It is native, it never sends your filesystem anywhere, and it is $4.99 once after a 14-day free trial.

Download Delve for macOS

06 Common questions

Why is my Mac's System Data so large?

Usually local Time Machine snapshots, which macOS stores on the internal disk several times a day. After that: application caches, iOS device backups in MobileSync, and Application Support data for apps that store large files outside their own folder.

Is it safe to delete System Data on Mac?

You cannot delete it as a unit, because it is not a folder. You delete the things inside it. Caches and old iOS backups are safe. Swap files, /System, and Application Support folders for apps you use are not.

What is the difference between System Data and Other storage?

Nothing. Other was the name before macOS Ventura; System Data is the name now. Same uncategorised remainder.

How do I reduce System Data quickly?

Thin local Time Machine snapshots with tmutil, empty ~/Library/Caches for apps you have quit, remove old iOS backups, and restart so macOS runs the cleanup it defers. That covers most of it on most Macs.

Why does System Data grow back after I clear it?

Because most of it is doing its job. Caches refill, snapshots are retaken, swap grows under memory pressure. A System Data figure that returns to 20 or 30 GB is normal. One that climbs past 100 GB and stays there is worth investigating.

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