I have attached to my SheevaPlug 2 Seagate 1.5 TB drives and a 16GB memory stick. I installed Gentoo and have been loading up the SheevaPlug with all kinds of software only to find my /usr and /var directories quickly consuming the 16GB.
So I decided to move /var and /usr off of the memory stick onto one of the hard drives. If you do the same, make certain you copy your files with their permission intact -- I neglected to do so and am paying the price to have to go back and chown/chgrp on several nodes.
What I first did after copying /var and /usr to the hard drive and removing /usr and /var was to create symbolic links named /var and /usr pointing to their respective directories on one of the Seagate drive, but I found certain software detected my ploy and wouldn't work, so I had to come up with something more solid.
Enter "mount --bind". Read up on the man page on mount; and this web page offered some perspective: http://aplawrence.com/Linux/mount_bind.html
So, your /etc/fstab might have entries like this:
/dev/sdb /mnt/seagateA ext3 noatime 0 0
/dev/sdc /mnt/seagateB ext3 noatime 0 0
/mnt/seagateA/var /var none bind
/mnt/seagateA/usr /usr none bind
I'm just trying this and will update if I have problems, but I thought I'd post this while it's on my mind so others needing to conserve space on their thumb drive and mapping out the larger branch to a hard drive would have something to consider.