EDIT: Sorry this post was a duplicate of the above initially, not sure what happened there...
If you're worried about reliability then the best thing to do may be to run a RAID 1 setup (or RAID 5 if you're planning on getting 3 or more drives.) You can partition those how you please, but if you use one of the above levels you'll ensure that if one of your drives goes down then you won't lose any of your data.