I'd try an alpha machine, with 66MHz-64bit PCI bus, and interleaved
memory access, to improve memory bandwidth. It costs around $10000
with 512MB of RAM, see SWT (or STW) or Microway. This cost is
small compared to the disks.
I've never had trouble with adaptec cards, if you terminate things
according to specs, and preferably use terminators on the cables, not
the card one. In fact I once had a termination problem, because I was
using the card for it... It hosed my raid5 array, because there were
two disks on that card...
Another advantage of the alpha is that you have more PCI slots. I'd
put 3 disks on each card, and use about 4 of them per machine. This
should be enough to get you 500GB.
If there are lots of network traffic this will likely be your
bottleneck, particularly because of latency.
Might I also suggest a good UPS system? :-) Ah, and a journaling FS...
