SpareDisk

What is System Data on Mac, and how do you reduce it?

System Data is the grey part of the storage bar in System Settings › General › Storage. Older versions of macOS called it “Other.” It often reaches 50 or 100 GB, and macOS doesn’t let you open it to see what is inside. Here is what it usually contains and how to reduce it safely.

By Manish Bhattacharya, maker of SpareDisk · Updated

What counts as System Data

System Data is everything macOS doesn’t put in one of its named categories. On most Macs that is a mix of:

  • Caches kept by apps and by macOS, in ~/Library/Caches and /Library/Caches.
  • Local Time Machine snapshots. If Time Machine is on, macOS keeps snapshots on the internal disk as well as on your backup drive.
  • Virtual memory. Swap files and the sleep image in /private/var/vm grow while memory is under pressure.
  • Logs and diagnostic reports.
  • App data in your Library: containers, Application Support folders, and virtual machine disks such as Docker’s Docker.raw or Parallels and UTM images.
  • Developer data that doesn’t show up under Developer, such as some tool caches in your home folder.

Why System Data grows so large

The usual causes are local snapshots after large file changes, a virtual machine or Docker disk that grew over time, an app that caches heavily (browsers, chat apps, AI coding assistants, video editors), and large swap files after a heavy workload. None of these is a problem in itself. They just take space you might want back.

How to reduce System Data safely

Restart your Mac

Restarting clears swap files and some temporary caches. If System Data drops by several gigabytes after a restart, virtual memory was part of it.

Let snapshots clear, or check them

macOS removes local snapshots automatically when it needs the space, and they are counted as purgeable. To see them, run tmutil listlocalsnapshots / in Terminal. Leaving them to macOS is safest.

Find the large folders in your Library

Much of System Data sits in your own Library folder, which Finder hides by default. A disk space analyzer shows which folders in it are largest. In SpareDisk, add your home folder as a location and open Library on the map. Caches, Containers and Application Support are the usual suspects. The app’s Developer and Leftovers screens name the tools and removed apps that own them.

Clear caches from the app that owns them

Most apps can clear their own caches. Browsers can clear cached images and files, Docker Desktop can remove unused images and volumes, and Xcode rebuilds DerivedData. Clearing a cache from the app is safer than deleting its folder while it runs.

Remove data left by deleted apps

Apps you deleted long ago can still have caches and containers in your Library. See how to uninstall apps completely.

What not to do

  • Don’t delete folders under /System, /private/var or /Library that you don’t recognize.
  • Don’t turn off System Integrity Protection to get at system files.
  • Be careful with “one-click clean” tools that remove whole categories at once. If you can’t see what will be removed, you can’t undo it.

What SpareDisk can and can’t see

SpareDisk is sandboxed and doesn’t ask for Full Disk Access. It scans only the folders you add. That covers most of the System Data you can safely reduce, since it sits in your home folder’s Library. It doesn’t read protected system areas, snapshots or /private/var. Its My Mac screen shows those as other used space rather than guessing what they are.

Questions

Is it safe to delete System Data on a Mac?
Not as a whole. System Data mixes caches you can clear with files macOS needs. Reduce it by restarting, letting snapshots expire and clearing caches from the apps that own them. Don’t delete system folders directly.
Why is System Data over 100 GB?
The usual causes are local Time Machine snapshots, a virtual machine or Docker disk image, large app caches, developer tools and swap files. Scanning your home folder’s Library with a disk space analyzer shows which of these applies.
Does restarting a Mac reduce System Data?
Often, yes. A restart clears swap files and temporary caches, which can free several gigabytes.
Was System Data called Other before?
Yes. Earlier versions of macOS showed much of the same data as Other in About This Mac › Storage.