I have a 500 GB external hard drive that I want to use with my new Mac (OS X Yosemite). I simply want to clear the external drive of everything that was on my old Mac (I don't want to transfer any files) and start from scratch. How would I go about doing this? Seagate doesn't address this question on their site and they have not responded to my inquiry.

When I attempt to erase using Disk Utility I get this error message:

Disk Erase failed with the error:
Couldn’t unmount disk.

1 Answer 1


Boot into the Recovery HD by holding ⌘R on boot and use Disk Utility on there. This way you can guarantee the disk is not being accessed and can be unmounted successfully.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .