Ubuntu External Drive Installation

[darb78]

I successfully installed Ubuntu 12.04 to an external 1TB drive. I set-aside about 1/3 of it for the system. I would like to set the other 2/3 up as a traditional USB drive that I can use with my macs as well as when I'm running Ubuntu. I've dug around but can't see to figure out how to make this happen. Thanks in advance!

[mikewhatever]

You probably need to format it with my macs. What's in the "other 2/3" now? Unallocated space? A partition? My macs should be able to see a partition, I assume.

[darb78]

Ok, I used my mac to format the drive as ExtFat to start and Ubuntu wouldn't recognize the drive. I changed the formatting to Mac Extended and now I can no longer use the hard drive to boot the computer. When I start the computer with the extra drive attached and hold down the Option key it fails to recognize that there is a drive attached. I have tried changing the disk format, however regardless of the formatting type the computer still fails to recognize it. Thoughts on how I can fix this without reinstalling?

[Vladlenin5000]

Whatever you do leave the partitions where Ubuntu has been installed alone, never touch them. Otherwise it won't boot, obviously. You should partition and format the remaining of the drive only, according to your needs.
If you formated the whole drive then you just deleted Ubuntu.

[oldfred]

Mac uses gpt partitioning?
Did you install Ubuntu with gpt partitioning?, default is usually MBR(msdos).

GPT Advantages (older but still valid) see post#2 by srs5694:
http://ubuntuforums.org/showthread.php?t=1457901
https://wiki.archlinux.org/index.php/GUID_Partition_Table#Advantages_of_GPT

Ubuntu will boot with either UEFI or BIOS from gpt partitioned drives. And Windows since Vista will read gpt data drives, but Windows only boots from gpt drives with UEFI.

You do not want hybrid drive:

http://www.rodsbooks.com/gdisk/hybrid.html