Reposted from an Apple Discussion question I just asked:
This is a somewhat long post, but the point is this: I have a new 1TB Fantom GreenDrive (attached via USB) which I cannot partition the way that I want to. I want to allocate 300G for a Time Machine backup partition and the remainder as a partition for everything else. For some reason, I’m only able to partition the drive so that it has two equal-size partitions. While this isn’t terrible (the 300G figure was somewhat arbitrary), I’m curious to see if anyone knows what’s going on here. As part of my tale, I list three “mysteries” that have really stumped me.
For at least a year now, I’ve had two external USB drives attached to my machine through a hub. One (a Fantom Titanium-II 500G drive) was for Time Machine, and the other (a LaCie 150G drive) was for other files. These drives were almost always connected to my machine, and they were almost always powered on. About three weeks ago, the Time Machine drive started unmounting, seemingly randomly, from the computer. When I tried to verify it in Disk Utility, it gave me an error, and the drive would again unmount. At the same time, I started having problems with the LaCie drive - when I plugged it in, the Mac gave me a message saying that the drive wasn’t working properly and that I had to back up everything on it.
This all seemed too coincidental to me, and so is the first mystery of my saga. However, I saw the GreenDrive on sale and decided to pick one up, rather than trying to fix the two drives. When I connected the GreenDrive to the computer, it was formatted at NTSF. When I tried to format it as Mac OS Extended (Journaled), Disk Utility gave me an error.
If I booted the Mac into Windows, I could format the drive again as NTSF, and it would work fine. When I went back into the Mac side, it worked there, too (that is, I could read from it and write to it). Also, I could use Disk Utility to format the drive as MS-DOS (FAT). Of course, I needed to format the drive for the Mac so that it would work for Time Machine.
When I went into the Time Machine preference pane and selected the GreenDrive for Backup (which was still formatted as MS-DOS (FAT) at the time), and did the erasing from within Time Machine, I was able to get the drive formatted as one large Mac OS formatted partition. Why I was able to successfully format it from Time Machine, but not from Disk Utility (which I believe is what Time Machine uses for the erasing, anyway) is the second mystery.
So, now I had a 1TB hard drive set up a single partition. I still wanted to divide it in two. However, when I tried using Disk Utility to partition it the way I wanted, I got an error saying the partition failed. Just as a test, I tried partitioning as two equal-size partitions, and this worked. Why it would let me partition in this configuration, and not the way I wanted, is the third and final mystery.
In the end, I’m almost where I want to be. I had to spend a little bit of money, but I have more total storage space available, and it seems to be working fine. Also, I was able to format the LaCie drive, and it seems to be working well, so it wasn’t a total loss. Still, any answers you guys can provide would be greatly appreciated.

