If you’ve purchased (or have otherwise come into possession of) an external USB hard drive, and you’re having trouble getting Disk Utility to play nicely with it (i.e. reformat it to HFS+), here’s a trick for you. Open Terminal and type the following:
cd /dev/ <return>
ls - | grep disk <return>
Take note of the disks displayed. Provided you have no other external hard drives attached, your culprit disk is probably going to be
Again in the terminal, execute the following:
diskutil eraseDisk HFS+ <desired hard drive name> disk1
This invokes the Disk Utility, commands it to erase the disk
disk1, rename it as
<desired hard drive name> and format the drive as HFS+, or MacOS Extended Volume Hard Drive Format.
Note: Use HFS+ if you intend to use the hard drive on Mac only. If you want to use it on PC or PC/Mac, you’re going to have to choose another option. For more detailed information, check out the Apple developers website.