Comment Re:the 2 main choices: (Score 4, Informative) 260
ZFS does this much more simply with no ugly hacks. You can have mismatched drives when you build a mirror (the mirror is the size of the smallest drive in the mirror set), and then you stripe across the mirrors. As the older, smaller drives fail, replace them with newer, bigger drives and the pool magically gets bigger. 100GB + 500GB mirrored (100GB usable). 100GB dies, swap in a 750GB drive and now this pool is automatically resized to 500GB. Get 2 more drives? Mirror them and add them to the pool and your pool expands with no one the wiser.
Seriously, if you haven't played with ZFS before, download FreeNAS and give it a whirl. When I was a Solaris admin, ZFS was the most fun thing to work with by far.