System Data on Mac is huge – what is it and how do you reduce it?

What is System Data on a Mac?

System Data is a catch-all category in System Settings › General › Storage (macOS 13 Ventura and later; on macOS 12 Monterey under “About This Mac › Storage”). Up to macOS 11 Big Sur it was called “Other”. It covers everything macOS doesn't classify as Applications, Documents, Photos or another fixed category.

Keep in mind that macOS calculates this category itself, and you can't expand it in Settings. The number also tends to lag behind and may only update after a while or a restart.

What's typically in System Data?

Usually a handful of large items are what inflate the category:

• Caches and logs from macOS and apps, e.g. in ~/Library/Caches and /private/var.
• Local Time Machine snapshots, which macOS frees automatically when space is needed.
• iPhone and iPad backups, plus downloaded software updates for those devices.
• Virtual machine disk images and the Docker Desktop disk image.
• App data in ~/Library/Application Support and ~/Library/Containers.
• Purgeable space: storage macOS can free on its own when needed.

How do I reduce System Data safely?

Start with a restart: macOS clears temporary files and recreates swap files in the process. Deleting caches by hand rarely pays off because they come back – only a single, unusually large cache from an app you know is worth a look.

Then tackle the big items one by one: local snapshots, device backups, virtual machines and developer data. Xcode data is covered in the guide “Free up Xcode disk space”.

How do I delete local Time Machine snapshots?

Time Machine creates local snapshots on your internal drive, and macOS frees their space automatically when needed. To list them, run tmutil listlocalsnapshots / in Terminal.

To delete a single snapshot, run tmutil deletelocalsnapshots 2026-10-28-101500 with the date from the list. Depending on your setup, this may require admin rights (prefix the command with sudo). Time Machine creates new snapshots after its next backup – that's expected.

How do I clean up iPhone backups, VMs and Docker?

Always remove this data through the app that owns it, not directly in the file system – that keeps references and databases consistent.

• iPhone and iPad backups: connect the device, select it in Finder, and delete old backups under General › Manage Backups.
• Virtual machines: delete VMs you no longer need inside the virtualization app itself.
• Docker: docker system prune removes stopped containers, unused networks, dangling images and the build cache; set the disk limit in Docker Desktop's settings under Resources.

Reduce System Data on your Mac safely

1. Restart your Mac

   Restart so macOS can clear temporary files and refresh the storage numbers.

2. List local snapshots

   Open Terminal and run tmutil listlocalsnapshots / to see existing snapshots.

3. Delete snapshots you don't need

   Delete individual snapshots with tmutil deletelocalsnapshots followed by the date from the list; add sudo if needed.

4. Remove old device backups

   Connect your iPhone or iPad, select it in Finder, and delete old backups under General › Manage Backups.

5. Clean up VMs and Docker

   Delete unused virtual machines in their app, and run docker system prune for Docker.

6. Check developer data

   If you use Xcode, clean up DerivedData, DeviceSupport and simulators as described in the Xcode guide.

7. Check the result

   Reopen the storage overview; the System Data figure can take a few minutes to update.

Frequently asked questions