External drives · Mounting and drive problems
Why does my Mac slow down or freeze when my external drive is plugged in?
Short answer: Usually the drive is struggling to read, Spotlight is indexing it for the first time, or a bad cable or hub keeps resetting it. Wait for indexing, try a direct connection and another cable, and run First Aid. Freezes with read errors suggest a failing drive.
A healthy drive shouldn't freeze your Mac. When it does, the usual causes are a drive that is struggling to read (macOS waits for it), Spotlight indexing a newly connected drive, or a flaky cable or hub that keeps resetting the connection.
How to narrow it down:
- Wait a few minutes after connecting — first-time Spotlight indexing finishes on its own.
- Try another cable and connect directly to the Mac.
- Run First Aid in Disk Utility.
- Open Activity Monitor → Disk to see what is reading the drive.
If the slowdowns come with read errors, clicking noises or files that won't copy, the drive may be failing — copy what matters off it now. See what to do when your fast drive seems to be failing.