I have a 2013 MacBook Pro and I'm trying to format an FD 4TB drive to use it with TimeMachine. In Disk Utility, when I try to either erase it, or repartition it, I'm getting an error that it can't unmount the disk.
Since it's not the boot disk, I don't understand why I'm getting that error.
I've tried verifying and repairing the disk, and no errors are found.
It is a self powered HDD, connected with a USB cable. Interestingly enough, swapping the cable fixed the problem, even though the disk would mount on the desktop and could be read and written to. I'm at a loss for how that could work, but formatting or partitioning it didn't.
It is a self powered HDD, connected with a USB cable. Interestingly enough, swapping the cable fixed the problem, even though the disk would mount on the desktop and could be read and written to. I'm at a loss for how that could work, but formatting or partitioning it didn't.
It is not uncommon that macOS won't allow the unmounting of a volume. It is usually because some process is still accessing the drive with the usual culprit being Spotlight indexing. Sometimes it will allow you to unmount the volume if you wait a minute & try to erase the drive/volume again.
Keep in mind if you have more than one volume or partition on that drive, the error could be due to another volume/partition being accessed.
Hi,
I just wonder if your 4TB external drive is HDD or SSD and drive is self powered drive or bus powered one which you didn't mention.
If Bus powered drive, especially if it's HDD one it might be lack of power to operate.
That might have been it.
MacBook Pro: Disk Utility error unmounting external drive
