I've been trying to format a 128 GB USB thumb drive as a Mac OS Extended volume (HFS+) but it silently fails and the only successful format I can do is MS-DOS FAT. As I want to use the drive to install a dev version of Lion, I need the HFS+ format and trying it in terminal gave the following result: Marks-MacBook-Pro:~ markbyrn$ diskutil eraseDisk HFS+ lion disk1 Started erase on disk1 Unmounting disk Creating the partition map Waiting for the disks to reappear Formatting disk1s2 as Mac OS Extended with name lion Initialized /dev/rdisk1s2 as a 128 GB HFS Plus volume Mounting disk Could not mount disk1s2 with name (null) after erase Finished erase on disk1 Marks-MacBook-Pro:~ markbyrn$ So it appears to initialize but won't mount. I also tried partioning the drive into 2 or 4 partitions and formatting an individual partition but that didn't work either. I have installed the dev version (preview 2) of Lion on a 16 GB thumb drive but there's not enough free space to do an update to preview 3. Any advice on how I can get this 128 GB thumb drive formatted?