“System Data” is huge – what is it really?
“System Data” is Apple's bucket for everything Storage
can't categorize – and on a developer Mac that's mostly your own
tools' caches: Xcode, Docker's VM, simulator runtimes, package manager
caches and Time Machine local snapshots. It's not a mystery and not
malware; it's reclaimable.
Break it down instead of guessing
du -sh ~/Library/Developer 2>/dev/null # Xcode: often 30-100 GB
du -sh ~/Library/Containers/com.docker.docker 2>/dev/null
du -sh ~/Library/Caches 2>/dev/null # all app & tool caches
tmutil listlocalsnapshots / | wc -l # local TM snapshotsThe usual suspects, in order
- Xcode – DerivedData, device support symbols, simulator runtimes. Full map →
- Docker / OrbStack VM disks – 30-100 GB is routine. Prune guide →
- Time Machine local snapshots – invisible copies of your disk kept on your disk. Guide →
- ~/Library/Caches – npm, pip, cargo, brew, browsers; every tool caches here and none clean up.
- Project build folders – node_modules, Rust target, Gradle builds scattered across the disk. Guide →
- iOS device backups – ~/Library/Application Support/MobileSync, tens of GB per device.
Why Apple's Storage panel won't help
System Settings → Storage lumps all of the above into one grey bar and offers to delete your photos instead. It has no idea what DerivedData or a cargo registry is – you need a tool that does.
CacheCleaner is exactly that tool: it walks your disk, names every developer cache in the grey bar, shows real sizes, and deletes only what you tick.
Get CacheCleaner for Mac