A nearly full startup disk can slow saves, exports, updates, Time Machine, and normal app behavior. macOS needs free space for swap files, caches, temporary files, and updates, so problems begin before storage reaches 100 percent.
This guide applies to recent macOS versions with System Settings.
Does This Affect You?
Use these steps if the Mac warns that the startup disk is almost full, storage is nearly all one color, or apps are sluggish when saving or exporting.
Use Storage Management
- Open System Settings > General > Storage.
- Wait for macOS to scan the disk.
- Open large categories such as Documents and Applications.
- Sort or review by size and remove items you recognize and no longer need.
- Review Apple’s recommendations, such as Store in iCloud or Empty Trash Automatically.
- Remove unused apps and empty Trash afterward.
Clear Obvious Space Hogs
- Open Downloads in Finder and sort by size.
- Delete old DMG installers, PKG files, ZIP archives, duplicate downloads, and unneeded videos.
- Empty Trash because deleted files still take space until then.
- In Mail, remove deleted items and old large attachments if needed.
- In Photos settings, enable Optimize Mac Storage if iCloud Photos is active and local space is limited.
- Restart after a large cleanup so temporary files can be released.
Storage Cleanup Notes
System Data or Other
System Data includes caches, logs, snapshots, and temporary files. It can be tens of gigabytes. Restarting and waiting for reindexing often reduces misleadingly large readings.
Old iPhone or iPad Backups
Device backups stored on the Mac can be large. Look for iOS Files in Storage Management or related Finder settings and remove backups you no longer need.
Move Large Libraries
Video, photo, and music production libraries are often better kept on an external SSD, with only active projects on the internal drive.
Check Quarterly
Review Storage settings every few months so Downloads, old backups, and forgotten installers do not become an emergency.
Sources
- Apple Support: Free up storage space on your Mac
- Apple Support: Storage settings on your Mac
- Apple Support: Manage storage for apps and files on Mac