Thank you for your question. It sounds like you would like to install Mavericks on a USB drive and would like to know the minimum size for the partition.
The following article will provide you steps for installing OS X on an external volume. It also states that "your storage device must have at least 13 GB available (after formatting) to install OS X Lion or later and a Recovery partition."
Once installed, you can select to boot to this installation of OS X by holding down the Option key when restarting your computer or set it as the Startup Disk in System Preferences. You can find more information in the following article:
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Thanks for your response, however it doesn't answer the question. We want to know if the GUID partition table is necessary (step 5), and if yes - can it be done with an existing partition/not harming another partition on the drive?
Not all of us students have 2 drives, or one we can borrow to accomplish this. Luckily I have a nice 'backup' usb drive, but I use one of the partitions for time machine. So these instructions are insufficient.
I found this article, which may help, but will also likely induce psychosis: http://support.apple.com/kb/PH14080
Title: "If you can’t install OS X on an external disk"
Instructions: "To check the external disk’s partition scheme..."
Wow. Just wow. Please someone shoot me.
Ok in all seriousness though, we just want to know if its safe & possible to create a bootable mavericks installer on an already partitioned external drive! I have an external drive with a GUID partition table scheme, but the first partition is for Time Machine, and it's not my mac's time machine backups. So is it OK to go ahead with making the second partition a bootable Mavericks installer?
Please, if you don't know the answer, or don't feel that a straight answer is better (ie. "no, and here are the reasons why") then please do not respond.