You should configure your discs to RAID 10 volumes.
You should set up a separate volume for WAL.
A volume for an additional table space may also useful.
In your case I would do 2 partitions:
1. RAID 10 with 8 discs for general data
raid 10 is of course not questionable. but are you sure that it will work faster than for example:
2 discs (raid 1) for xlog
6 discs (raid 10) for tables
6 discs (raid 10) for indices?
depesz
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