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

Julio Jean Fils — Sat, 18 Jul 2026 02:50:14 +0000

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

My results:

30G    ~/Library/Caches
465M   ~/Library/Logs
70G    ~/Library/Developer

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

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

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/*

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

Or, if you want a full reset:

xcrun simctl erase all

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/*

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

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.

DEV Community: Julio Jean Fils