What Is System Data Storage on Mac? How to Shrink It

Open System Settings → General → Storage and the biggest segment of the bar is often the vaguest one: System Data. It's the catch-all for everything macOS can't file under Apps, Photos, or Documents — and it can quietly grow past 100 GB. Here's what's actually inside it, and which parts are safe to shrink.

What actually lives in System Data

Despite the name, System Data is mostly not the operating system — macOS itself lives on a separate, sealed, read-only volume. System Data is working data:

• Caches in ~/Library/Caches and /Library/Caches — browsers, streaming apps, and developer tools are the heavyweights.
• Local Time Machine snapshots, which hold hourly copies of changed files on the startup disk.
• App support files in ~/Library/Application Support, including old iPhone and iPad backups under MobileSync/Backup.
• Logs in ~/Library/Logs and /var/log.
• Virtual memory — swap files and the hibernation image macOS manages itself.
• Sandboxed app containers in ~/Library/Containers.

On macOS Monterey and earlier this same bucket was labelled "Other." Ventura, Sonoma, and Sequoia all call it System Data and show it in the same place: System Settings → General → Storage, at the bottom of the category list. Some churn is normal — a macOS update can temporarily add tens of gigabytes of staged files, and the number swings as snapshots come and go. It's worth investigating when System Data stays above 60–80 GB for days, not when it spikes for an afternoon.

Measure the big folders yourself

The Storage pane won't itemize System Data, but Finder will:

1. In Finder, press Shift-Cmd-G and go to ~/Library.
2. Switch to list view, press Cmd-J, and tick Calculate all sizes.
3. Click the Size column header so the biggest folders float to the top. Caches, Application Support, Containers, and Developer are the usual suspects.

Or take the same measurement in Terminal — this is read-only and changes nothing:

# sizes of the usual suspects
du -sh ~/Library/Caches ~/Library/Logs ~/Library/"Application Support" 2>/dev/null

Expect a few gigabytes in Caches on a working Mac — browsers and streaming apps cache aggressively by design. What you're hunting is the outlier: a single app folder holding 20 GB it never cleans up.

The safe wins

• Time Machine snapshots. Run sudo tmutil thinlocalsnapshots / 999999999999 4 to clear them. A deleted snapshot can't be restored, but your real backups are untouched, hourly snapshots resume immediately, and they auto-expire after about 24 hours anyway.
• Old device backups. iPhone backups can hold tens of gigabytes. Delete them from the device's Manage Backups dialog in Finder rather than trashing the raw MobileSync folders — see the folder path above only to check sizes.
• Developer caches. If you use Xcode, ~/Library/Developer/Xcode/DerivedData is safe to delete entirely; Xcode rebuilds it on the next build.
• App caches. Inside ~/Library/Caches, delete the folders of apps you recognize. Apps recreate their caches automatically the next time they run — that regeneration is your undo.

What to leave alone

Don't gut Application Support or Containers folders for apps you still use — that's real data (chat archives, project files, licenses), not cache. Leave swap and the hibernation image to macOS; it sizes them dynamically and deleting them buys nothing lasting. And never delete anything under /System. If a single log or cache file has grown to multiple gigabytes, the better fix is the misbehaving app writing it, not repeated deletion.

Caches come back — that's the point

Anything genuinely cache-like will regrow, so treat cache-clearing as a periodic sweep, not a one-time fix. For a deeper pass on caches specifically, see our guide to clearing the cache on your Mac.