If you're using hardware RAID, swap on your RAID array shouldn't hurt
you any because your RAID controller is taking care of it, and Linux
just sees one big disk so having multiple swap partitions on different
disks isn't an option anyway.

But it sounds like you're running software RAID, in that case I'd go
with the two different swap partitions, one on each disk. It just
doesn't make much sense to write your swap file to two different disks
when you're CPU has to deal with the RAID operations. Your data isn't
going to be hurt if swap fails, and a degraded RAID array won't impact
swap file performance with the two drive setup.

This is how I've always delt with RAID and swap.

--
Andrew S. Zbikowski | http://andy.zibnet.us
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