I've got a box cobbled together to run as my NAS. Athlon64 3200+ 1GB ECC Memory ATI x1300pro video card 3x 640GB AAKS WD hard drives in RAID5 (SATA drives) 1x 15GB drive for OS (IDE drive; OS is Gentoo using md for RAID management) But it's getting pretty full. (only have 150GB free space). The drives are $70 on ZipZoom and $75 on NewEgg. Here's the question. I'm sure that sometime after adding a 4th drive to the array (md lets you just add a drive to expand the array) I'll want more space, and at that time, the only answer will be to use larger drives, replacing all 4. Would I be better off getting a 640GB drive now, or installing something larger so that I only need to upgrade 3 drives down the road? A third option, I guess, would be to add a controller/RAID card so that I can go past 4 drives in the array.