How to Clear 100GB+ of 'System Data' on a Mac in 10 Seconds (The Hidden Time Machine Snapshot Fix)

We see this exact frustration at our Chicago Mac bench almost every day:

You are trying to download a macOS update (or run the OpenCore Legacy Patcher No-USB Upgrade), and your Mac says “Not enough free disk space.”

1. So you delete 60GB of old movies and downloads.
2. You empty the Trash.
3. You open System Settings → General → Storage… and your free space didn’t go up by a single gigabyte! Instead, the gray “System Data” bar just grew larger by 60GB.

Before you waste $40 on sketchy “Mac Cleaner” bloatware apps, here is the real technical reason this happens—and the 10-second built-in Apple Terminal command that frees 50GB to 150GB of trapped storage instantly.

Why Deleting Files Doesn’t Free Up Space (The APFS Snapshot Trap)

Modern Macs use APFS (Apple File System). Whenever Time Machine is enabled—or even when macOS prepares for a software update—APFS silently takes invisible Local Snapshots of your drive so you can roll back files.

When you delete a 40GB folder and empty the Trash, macOS does not actually erase those 40GB from your SSD if a local snapshot is still holding onto a reference to those blocks. Instead, macOS reclassifies those 40GB from “Documents” into the mysterious gray “System Data” bar!

⚡ Fix 1: The 10-Second Terminal Command to Purge Hidden APFS Snapshots

You can force macOS to release all trapped local snapshots immediately using Apple’s built-in tmutil (Time Machine Utility) command:

1. Open Terminal (press Command + Space, type Terminal, and press Enter).
2. Copy and paste this exact command and press Enter:

tmutil thinlocalsnapshots / 99999999999 4

3. What you will see: Terminal will output a list of purged snapshot dates (Thinned local snapshots: com.apple.TimeMachine.2026-...).
4. Open Disk Utility or System Settings → General → Storage and wait 15 seconds: you will often watch 30GB to 150GB of trapped “System Data” vanish right before your eyes!

(Note: This only clears temporary local snapshots on your internal drive; it never deletes anything on your external backup hard drive or your personal files).

Fix 2: The Hidden 50GB macOS Sonoma / Sequoia Aerial Screen Saver Cache

Did you click on one of Apple’s pretty slow-motion flyover wallpapers or screen savers in macOS Sonoma or Sequoia?

Behind the scenes, macOS downloads massive 4K 240fps uncompressed video files into a hidden system folder that can quietly balloon to 20GB to 60GB inside System Data.

How to Delete the Aerial Video Cache:

1. Open Finder.
2. In the top menu bar, click Go → Go to Folder… (or press Command + Shift + G).
3. Paste this exact folder path and press Enter:

/Library/Application Support/com.apple.idleassetsd/Customer/4KSDR240FPS

4. Inside that folder, you will see dozens of giant .mov video files (often 500MB to 2GB each).
5. Select those .mov video files, move them to the Trash (enter your Mac password when prompted), and Empty the Trash.

Fix 3: Forgotten Old iPhone & iPad Backups (MobileSync)

If you ever backed up an iPhone or iPad to your Mac using Finder or iTunes years ago, a single forgotten backup can sit inside System Data eating 60GB to 256GB forever.

1. Open Finder and press Command + Shift + G.
2. Paste this path and press Enter:

~/Library/Application Support/MobileSync/Backup

3. Any numbered folders inside here are full iPhone/iPad backups. Delete any old device backups you no longer need (or manage them cleanly via System Settings → General → Storage → iOS Files).

Fix 4: Clear Safe User App Caches (~/Library/Caches)

Apps like Google Chrome, Spotify, Slack, Discord, and Adobe Premiere store gigabytes of temporary cache data inside your user library:

1. Quit all open apps.
2. In Finder, press Command + Shift + G (make sure to include the ~ tilde symbol at the beginning!):

~/Library/Caches

3. Sort the folders by Size to spot any runaway cache folders (like com.spotify.client, Google/Chrome, or Adobe) and drag the contents of those specific oversized cache folders to the Trash, then restart your Mac.

Still Out of Space on a 128GB or 256GB MacBook?

If your internal SSD is simply too small for modern macOS and your photo library, many 2012–2017 MacBook Airs, Retina MacBook Pros, and iMacs can be physically upgraded to a blazing-fast 1TB or 2TB NVMe SSD in under an hour!

• Read our DIY MacBook NVMe SSD Upgrade Guide to see if your model has a removable SSD slot.
• Or bring your Mac to Arbor Mac iPhone Repair in downtown Chicago (8 S Michigan Ave, Suite 312, across from Millennium Park) for a same-day SSD upgrade and complete data clone. Check your Mac upgrade price in 10 seconds →