How you partition the external drive is entirely up to you but case 2 is a good way to go.
Partition the drive with a 200GB and 50Gb (give or take) and use the 200 for Time Machine and the 50 for a Bootable partition.
Although the drive worked straight out of the box, it will need to be formatted as HFS+(Journaled) using the GUID partition table.
This will ensure that the drive is capable of booting an Intel Mac. If formatted in using the previously normal Apple table, the drive will only be capable of booting a PPC Mac. Disk Utility will take care of that for you, it's under options in the Partition tab.
Disregard the software that came with the drive if you plan to use the drive for Time Machine. Only format and partition the drive using the Disk Utility in OS X.
If you need any more information, just holler
I recently purchased a 250GB external drive, primarily for Time Machine. My system has a 150GB drive of which 50GB is used (and 100GB is free).
How should I allocate space on the new drive?
Based on past discussions on this BB the suggestion was to allocate 200GB for Time Machine. Should I just have:
1. one 250GB partition on the new drive and allocate it all to Time Machine or
2. should I have two partitions: a 200GB Time Machine partition and a 50GB partition for other uses?
In case 2, could I put a bootable partition on the drive to be used if the drive inside the imac fails?
Note, partition is probably not the right word.
I'm not sure how to any of the above. The drive (a Seagate FreeAgent) worked right out the box when attached to a USB port. A reboot was not necessary, and an icon for the drive appeared on the Desktop.
The drive includes manuals and software for mac formating. I have not read the manuals yet, and please excuse this post if all the answers are in the manuals.
My system is now OSX 10.4.11 with 512MB RAM and 150GB internal and 250GB external drives.
Soon, the system will be OSX 10.5.? with 2GB RAM and 150GB internal and 250GB external drives. (? is the current release of Leopard; I don't remember if it's 1 or 2.)