Why Is System Data So Large on Mac? (100 GB+ Explained and Fixed)

“System Data” (called “Other” on older macOS versions) is the catch-all category in your Mac’s Storage view. A few dozen gigabytes is normal. When it reaches 100 GB or more, something specific is almost always to blame. This guide shows how to find it. For the full step-by-step removal guide, see how to clear System Data.

First: get an accurate number

Open System Settings → General → Storage and let it finish calculating — the first number shown is often too high. Then restart your Mac and check again: a restart clears swap and temporary files and gives macOS a chance to purge snapshots it no longer needs.

Cause 1: Time Machine local snapshots

If Time Machine is on, macOS keeps hourly local snapshots on your internal disk, especially when the backup drive isn’t connected. They are counted as System Data.

tmutil listlocalsnapshots /

If you see many entries, connect your backup drive and let a backup finish, or delete old ones by date:

sudo tmutil deletelocalsnapshots 2026-09-15-101500

macOS removes snapshots automatically when space is needed, but the Storage bar doesn’t always reflect that right away.

Cause 2: Old iPhone and iPad backups

Each local device backup can be tens of gigabytes, and old ones are never removed automatically. Look in:

~/Library/Application Support/MobileSync/Backup

Or connect the device, select it in Finder’s sidebar and click Manage Backups to delete old ones.

Cause 3: Xcode, simulators and developer tools

If you have ever installed Xcode, check ~/Library/Developer. DerivedData, iOS DeviceSupport files and old simulator runtimes easily reach 50 GB or more.

du -sh ~/Library/Developer/* 2>/dev/null
xcrun simctl delete unavailable

Our developer cleanup page explains which folders are safe to remove.

Cause 4: Docker, virtual machines and emulators

Docker Desktop stores containers and images in a single disk-image file that grows but rarely shrinks; UTM, Parallels and VMware store whole virtual machines as files. Check their size in each app’s settings, and reclaim Docker space with:

docker system prune

(Read what it will delete before confirming — it removes stopped containers and unused images.)

Cause 5: Caches and logs

Browsers, streaming apps, design tools and chat apps can each keep several gigabytes in ~/Library/Caches. Logs and crash reports live in ~/Library/Logs. See how to clear cache safely.

Cause 6: Leftovers from deleted apps

Dragging an app to the Trash leaves its support files behind in ~/Library/Application Support and ~/Library/Containers. Games, video editors and virtual instruments can leave very large folders.

Find the biggest folders yourself

This lists the largest folders in your Library, biggest last:

du -sh ~/Library/* 2>/dev/null | sort -h | tail -15

Work down from the top, but never delete Keychains, Preferences or the containers of apps you still use.

What not to do

• Don’t disable System Integrity Protection or delete anything in /System — it won’t reduce System Data in a useful way and can break macOS.
• Don’t erase your disk to fix the number unless you have a full backup and a real reason.
• Don’t trust “cleaners” that promise to delete System Data in one click without showing you what’s inside.

The quicker way

A MacDiskCleaner scan breaks down the user-level caches, logs, developer data and app leftovers that make up most of System Data, with sizes, and moves what you select to the Trash. Scanning is free, so you can see where your space went before deciding anything.