I've created a Mountain Lion install disk on a partition on an external USB disk which also has a Lion installer. Both appeared as Mac OS X Install ESD when mounted in Finder, but I renamed them and this rename persists across unmount/remount. However, when I reboot holding down the Option key to select the volume to boot from, both of these partitions appear as just Mac OS X so, other than booting from one, I don't know which is which. From this, I take it that in Finder it is just the mount point (in /Volumes) that has been renamed, not the partition name on the disk? Is there anyway to rename the actual partition name on the disk?