What’s happening here is that your MyBook Studio is still flagged as the active Time Machine destination, even though you’ve toggled Time Machine off. macOS doesn’t “forget” a drive until you explicitly remove it from the Time Machine configuration. That’s why every time you plug it back in, the OS sees it as the last known backup volume and tries to continue the unfinished backup session.
I suggest the following to break that link so the drive just behaves like normal external storage again:
- On your Mac, go to System Settings > General > Time Machine.
- You should see your MyBook Studio listed as a backup disk. Select it and choose Remove Backup Disk. This unlinks the drive from Time Machine.
If you’ve already turned off Time Machine and don’t see the disk listed, the OS may be hanging onto cached Time Machine preference files. In that case, we can remove them manually with a command in Terminal.
Not to worry, this won’t delete any of your files on the drive, it only resets the system’s idea of what drives are used for Time Machine. Here’s how:
- Open Terminal (you’ll find it in Applications > Utilities, or just Spotlight search it).
- Copy and paste this command, then hit Return: sudo rm /Library/Preferences/com.apple.TimeMachine.plist It’ll ask for your Mac login password — type it in (it won’t show characters as you type) and press Return.
- Next, restart your Mac. This forces macOS to rebuild the Time Machine preferences from scratch.
- After reboot, check System Settings > General > Time Machine. It should now be empty — no backup disks listed.
From that point on, plugging in your MyBook Studio will only mount it as a normal external drive.
