i never tested a sata array. the last generation were crappy.
the connectors were crappy, and christian used them, and always seemed to have issues.

if you start doing multi-disc scsi, the price soon starts creeping up to xserve levels.

it just isnt possible to acquire and test all the storage options, and evaluate their performance with catalyst.
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the main advantage of xserve RAID is networkability- you can share the storage at very high speed.
Using a fibre switch and XSAN you can create multiple disc volumes in the same unit and share them between different servers - thats the theory.

With the cheapest xserve raid which ships with 4 discs you would divide the thing up into 2 two disc raid sets, with the most expensive it might be possible to drive 6 computers at the same time.

I have a 14 disc xserve raid on a show at the moment, and im waiting for results.