I have a case from a rack mount UPS which looks like it could happily hold a bunch of drives and is deep enough to hold a few other things. I want to build a computer in there to host some drives. basically I'm thinking it will need PCI for a SATA card, and gigabit ethernet. Besides that, I want it to be able to share via AFP and ideally use Bonjour. It will need to run either software RAID or have a compatible low cost SATA RAID card available, and run VNC, preferably to work with Apple Remote Desktop.

I figure this leaves me the option to run some flavour of Linux, or try to build a hackintosh. Will Linux run the services I want?
I'm looking for suggestions for both sotware and hardware solutions. I need the smallest board possible which has plenty of SATA ports or expansion slots for them. Overall system speed and CPU are not immensely important. Something a year or two old will probably suffice. The point is to do this as cheaply as possible. I'm not looking for Xserve RAID performance. I just want to be able to hold large amounts of data with redundancy and the hardware needs only do a reasonable job of keeping up with gigabit ethernet. Its for streaming media across a local network and keeping it safe.

Any shuttle PC should do the job.  That way you could have on board SATA and not need a PCI card and in turn take up less space.  The mobo's are pretty small in those and since its x86 hardware you could run any version of linux you want.

But how man SATA ports are we talking? This box I have could hold 10 drives or more no problem. Thats the sort of size I'm going for.

OK, my new plan involves recycling the old logic board and CPU from a DA I used to use at work. It was donated when one of the USB ports came out of its socket. If you shove it back in and leave a cable connected, it works perfectly, otherwise it powers off or crashes, but that isn't an issue in this case, it will be rare I need even one USB port on it.
Anyone know the maker of this card:

http://eshop.macsales.com/item/Norco%20Technologies/NORCO4618/

It ticks all the boxes except I would really have loved to have RAID 5 in place.
Anyone know anything about this one:

http://www.newegg.com/Product/Product.aspx?Item=N82E16816115022

The price isn't too much worse, since I might well have used two of the cheaper ones. If I only have one card, I might be able to use a riser to flatten it 90 degrees against the board. That gives me plenty of space for the drives and some cooling.

The first one you linked from OWC must be decent as they only carry quality products.  eSATA gives you more options also.

DONT BUY THE NORCO!!! I bought it and it's based off the Silicon Image chip set. The driver that Silicon Image has causes kernel panics on any vs. of OS X older than 10.2. I have tried just about every card except the High Point and they are almost all based off the Silicon Image chip set. I settled on the Sonnet Tempo, it runs great and supports up to 20 drives with port multipliers. I have heard good things about the High Point though.

OK, thanks for the tip. Does the Sonnet do RAID 5? The more I think abot it, RAID 5 is going to be absolutely essential. I Need redundancy otherwise I may as well keep shoving bigger single drives into my MDD or Xserve.

No I don't think it does. The High Point you linked to on new egg would be a good thing to try.

Sorry if my advice sucked..  I have no experience with SATA RAID's.

If I go this route using the DA bits and Highpoint card from Newegg, I can get 8 HDs running happily in the box. (The issue of being able to afford them is another matter.)
There is room to add another Highpoint card later on with a second bank of 8 HDs. The beauty is I can add a dual CPU module to the board (I can, can't I?), and in those circumstances I should be literally doubling my storage with no performance hit.
I have thought about fibre channel, but I think gigabit ethernet will be plenty for my needs. I can add a second one of those too. It would be worth testing the two separate RAID sets when using one NIC and an IP each, see its faster than just using the one NIC for both.

Since I already have almost everything I need bar the controllers and the drives, I figure I can get the first bank up and running at 4TB (unformatted) for about £650 which is $1300. Should be over 3TB with parity and formatting. Thats not bad at compared to an Xserve RAID.
I could settle for 2.4TB for £460/$920. Should end up around the 2TB mark.
A 1TB Xserve RAID costs £4200 over here.

I must stop getting excited about projects I can't afford to finish.