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Julio Jean Fils
Julio Jean Fils

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

#tools #productivity #beginners #tutorial

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
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My results:

30G    ~/Library/Caches
465M   ~/Library/Logs
70G    ~/Library/Developer
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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
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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
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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/*
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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
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Or, if you want a full reset:

xcrun simctl erase all
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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/*
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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

  1. Open Storage and confirm System Data is huge
  2. Run: 
du -sh ~/Library/Caches ~/Library/Logs ~/Library/Developer ~/Library/Containers/com.docker.docker 2>/dev/null
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  1. Clear Docker if you use it
  2. Clear Xcode DerivedData / DeviceSupport / Previews
  3. Clean unused simulators
  4. Clear obvious app caches
  5. Restart
  6. 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.

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