Mac: storage is full and what is System Data
A message saying your startup disc is almost full can stop updates and slow your Mac. System Data is one of the biggest mysteries on the storage screen, so this guide explains it and shows how to free space safely.
See what is using the space
Open the Apple menu, then System Settings, General and Storage. On older versions, choose the Apple menu, About This Mac, then Storage and Manage. Wait a moment for the coloured bar to fill in.
What is System Data?
System Data is a mix of things macOS needs: temporary files, caches, logs, and some other items that Apple does not sort into other groups. It can grow to be quite large. It is normal for it to take a share of the space. It is not something you should try to delete by hand, because removing the wrong files can stop your Mac working.
Safe ways to free up space
- Empty the Trash. Right-click the Trash icon in the Dock and choose Empty Trash.
- Open your Downloads folder and delete old installers and files you do not need.
- In the Storage screen, look at the recommendations from Apple, such as Store in iCloud or Empty Trash Automatically. Read each one before turning it on.
- Delete apps you no longer use from the Applications folder.
- Move large photos and videos to an external drive. Check they open from the drive before deleting the originals.
Restart
System Data often shrinks after a restart, because temporary files are cleared. Restart, then look at the Storage screen again.
Avoid cleaning apps
Be careful with free clean-up apps or tools that promise to clear System Data. Some delete the wrong things and some are scams. If you are unsure, ask us first.
When to get more help
Contact us if System Data stays huge (for example over 100 GB) after a restart, if your Mac keeps saying the disc is full, or if you are unsure what is safe to delete. Back up your Mac before any big clear-out.