My Mac Said “System Data” Was Using 300 GB. Here’s How I Actually Cleared It.

I opened System Settings → General → Storage and stared at the screen for a second. macOS: 47 GB. Fine. System Data: 300 GB. No delete button. No info icon. Just a giant mystery bucket eating my disk. If you’ve hit the same wall: you’re not alone, and no — Apple doesn’t let you “delete System Data” from that screen. You have to find what’s hiding inside it and clear that yourself. Here’s exactly what I did. First: System Data isn’t one thing “System Data” (used to be called “Other”) is a junk drawer. It can include: App caches Xcode build leftovers and simulators Docker images and volumes Logs Local Time Machine snapshots Random stuff that doesn’t fit neatly into Apps, Documents, or Photos So the goal isn’t to delete “System Data.” The goal is to find the heavy folders and remove what’s safe. Step 1: Find what’s actually big I ran this in Terminal: du -sh ~/Library/Caches ~/Library/Logs ~/Library/Developer 2>/dev/null Enter fullscreen mode Exit fullscreen mode My results: 30G ~/Library/Caches 465M ~/Library/Logs 70G ~/Library/Developer Enter fullscreen mode Exit fullscreen mode Already interesting. Logs were tiny. Caches and Developer were not. Then I dug deeper: du -sh ~/Library/Developer/* 2>/dev/null | sort -hr | head -20 du -sh ~/Library/Caches/* 2>/dev/null | sort -hr | head -20 du -sh ~/Library/Containers/com.docker.docker 2>/dev/null Enter fullscreen mode Exit fullscreen mode That’s when the real picture showed up. What was eating my disk Culprit Size Worth clearing? Docker 63 GB Yes Xcode iOS DeviceSupport 21 GB Yes iOS Simulators 28 GB Yes Xcode Previews + Interface Builder cache 16 GB Yes DerivedData 3.6 GB Yes App caches (Chrome, CocoaPods, Yarn, etc.) ~30 GB Mostly yes That’s roughly 160 GB of reclaimable space — a huge chunk of that scary “System Data” number. If you do iOS or Docker work, this is extremely common. Your Mac isn’t broken. It’s just holding onto old build artifacts like a digital hoarder. Step 2: Clear the safe stuff 1) Docker (biggest win for me) docker system prune -a --volumes Enter fullscreen mode Exit fullscreen mode This removes unused images, containers, and volumes. If you’re not actively using those images, they’re just sitting there renting space. After pruning, quit Docker Desktop so the disk image can shrink. 2) Xcode leftovers rm -rf ~/Library/Developer/Xcode/iOS\ DeviceSupport/* rm -rf ~/Library/Developer/Xcode/DerivedData/* rm -rf ~/Library/Developer/Xcode/UserData/Previews/* rm -rf ~/Library/Developer/Xcode/UserData/IB\ Support/* Enter fullscreen mode Exit fullscreen mode What this does, in plain English: DeviceSupport = old symbol files from phones you’ve plugged in DerivedData = build cache (Xcode will recreate it) Previews / IB Support = SwiftUI + Interface Builder cache (also regenerates) You’ll maybe wait a bit longer the next time you build or open a preview. That’s it. 3) Simulators xcrun simctl delete unavailable Enter fullscreen mode Exit fullscreen mode Or, if you want a full reset: xcrun simctl erase all Enter fullscreen mode Exit fullscreen mode Simulators are useful… until you have years of old device data hanging around for no reason. 4) App caches rm -rf ~/Library/Caches/Google/* rm -rf ~/Library/Caches/CocoaPods/* rm -rf ~/Library/Caches/org.swift.swiftpm/* rm -rf ~/Library/Caches/JetBrains/* rm -rf ~/Library/Caches/Yarn/* rm -rf ~/Library/Caches/pnpm/* rm -rf ~/Library/Caches/ms-playwright/* Enter fullscreen mode Exit fullscreen mode Caches are meant to be temporary. Deleting them is usually fine. Apps just rebuild what they need. Step 3: Restart This part matters more than it should. macOS Storage numbers often don’t update live. After cleanup, restart your Mac, then check Storage again. Don’t panic if the number doesn’t drop instantly. What I would not delete A few ground rules that saved me from making it worse: Don’t randomly delete stuff under /System Don’t go nuclear on /Library unless you know the folder Don’t delete anything just because the name looks unfamiliar If you’re unsure, measure first (du -sh), delete second Clearing space should feel boring and controlled — not like defusing a bomb. A simple checklist you can reuse Open Storage and confirm System Data is huge Run: du -sh ~/Library/Caches ~/Library/Logs ~/Library/Developer ~/Library/Containers/com.docker.docker 2>/dev/null Enter fullscreen mode Exit fullscreen mode Clear Docker if you use it Clear Xcode DerivedData / DeviceSupport / Previews Clean unused simulators Clear obvious app caches Restart Recheck Storage The takeaway That 300 GB “System Data” number looks scary because Apple gives you almost no explanation and no delete button. But in practice, especially if you develop software, it’s often just: Docker Xcode Simulators Caches Find the heavy folders. Delete the regenerable junk. Restart. Your Mac suddenly feels a lot less haunted. Written after reclaiming a ridiculous amount of space from macOS System Data. If this helped, send it to the friend who’s currently convinced their Mac is possessed.