questions about disk configurations

hi
i have a question about best harddisk configuration for postgresql
performance.
of course i know that:
- scsi is better than ide
- 2 disks are better than 1
- 3 disks are better than 2

i know that with 3 disks one should move xlog to one drive, index files
to second and tables to third.
that's clear.

but:
will making software raid on this discs provide performance increase or
decrease?
which raid (0,1,5,10?) is best for postgresql? maybe it differs when it
comes to different datatypes (i.e. raid "X" is best for indices, but "Y"
best for tables).

i'd like to know what are the options to store all this information
(xlog, indices and tables). what configurations are best, what medium
and what should be avoided at all cost.

hope you can help me, and sorry for my english.

depesz

--
hubert depesz lubaczewski http://www.depesz.pl/
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Mój Boże, spraw abym milczał, dopóki się nie upewnię, że naprawdę mam
coś do powiedzenia. (c) 1998 depesz