Just bought a Backup Plus Slim Portable Drive from Seagate. Can't use for Time Machine because it's not in the correct format. The partition tab in Disk Utility is greyed out, and the Erase fails with the error message: "Couldn't unmount disk". What should I do? How can I reformat it??
Thanks very much!!
MacBook Pro, OS X El Capitan (10.11.4)
Reboot the computer and try again
I had this problem today. The set-up software that came on the drive did nothing to change the format and Disk Utility failed a bunch of times for me as well, so I took to Terminal. From the Command-Line, Part 1 showed me how to reformat the drive.
diskutil eraseVolume JHFS+ New /Volumes/DriveName
However, even after the drive was formatted correctly, Disk Utility would not allow me to partition it, so I had to use Part 2 and the Terminal to do that as well.
diskutil partitionDisk /dev/disk2 GPT JHFS+ First 100g JHFS+ Second 900g
I don't know if you are still having problems with this, but if you are, try this guide. It worked for me and now Seagate is divided into two partitions, one of which is set for Time Machine.
Seagate Erase Failed - Can't Reformat Drive
