Why does System Data keep growing?

Snapshots, caches and backups accumulate between restarts and updates. macOS reclaims much of it when free space runs low, so a large number on a mostly empty disk isn’t a problem by itself.

Can I delete System Data entirely?

No. Part of it is what macOS needs to run. You can shrink the reclaimable parts: backups, snapshots and developer caches.

Does reinstalling macOS reduce System Data?

Sometimes, but it’s rarely needed. Try the steps above first; they recover most of what a reinstall would.

Mac file guides

Why is System Data so large on my Mac, and how do I shrink it?

By Vishva Variya · Updated October 31, 2026 · 6 min read

Short answer

System Data is everything macOS can’t sort into another category: caches, logs, local Time Machine snapshots, iPhone and iPad backups, virtual memory and app support files. Restart first, since that clears temporary files. Then remove old device backups, delete Xcode caches if you develop, and check for local snapshots with tmutil. Don’t delete files in system folders by hand.

What’s inside System Data?

Caches and logs that apps and macOS write as they run.
Local Time Machine snapshots, kept until space is needed.
iPhone and iPad backups made by Finder.
Virtual memory (swap) and the sleep image.
App support files, developer tools and simulators.

Its size swings by gigabytes from day to day, and the Storage bar is only an estimate.

What are the safe ways to shrink it?

1Restart the Mac. Temporary files and swap are cleared on restart.
2Install pending macOS updates; leftover update files are removed afterwards.
3Empty the Trash, and Recently Deleted in Photos.
4Delete old iPhone and iPad backups: System Settings › General › Storage, then the ⓘ next to iOS Files.

How do I check for Time Machine local snapshots?

tmutil listlocalsnapshots /

Snapshots are listed by date. macOS deletes them on its own when space is short, so you rarely need to; to remove one now, use sudo tmutil deletelocalsnapshots followed by the date part of its name.

I use Xcode. What can I remove?

DerivedData (~/Library/Developer/Xcode/DerivedData) is a build cache. It’s safe to delete; Xcode rebuilds it.
Simulators for runtimes you no longer have: xcrun simctl delete unavailable.
Old simulator runtimes: Xcode › Settings › Components (or Platforms).

What should I not delete?

Anything in /System, /private or /Library you don’t recognise.
Whole app folders in ~/Library/Application Support while the app is still installed.
Cache folders an app is using right now; quit the app first if you must.

“Cleaner” apps that wipe caches give the space back only briefly: apps rebuild their caches as soon as they run.

Where Peekaboo fits

Peekaboo doesn’t touch System Data, on purpose: it works only with your own files, so nothing it does can break an app. For a breakdown of System Data itself, a disk analyzer with an admin scan, like DaisyDisk, goes further. What Peekaboo does is clear the rest of the bar, the downloads, videos, old installers and duplicates, with every cleanup undoable.

1Open Space Map to see which of your own categories are largest.⇧⌘M
2Run Clean Up and Duplicates, and review before anything moves.⇧⌘K

Questions

Why does System Data keep growing?: Snapshots, caches and backups accumulate between restarts and updates. macOS reclaims much of it when free space runs low, so a large number on a mostly empty disk isn’t a problem by itself.
Can I delete System Data entirely?: No. Part of it is what macOS needs to run. You can shrink the reclaimable parts: backups, snapshots and developer caches.
Does reinstalling macOS reduce System Data?: Sometimes, but it’s rarely needed. Try the steps above first; they recover most of what a reinstall would.