Bo,

> 2 - 2.4 Ghz Xeon processors
> 4GB ram
> 4 36gb 10000rpm scsi drives configured for raid 10

Hopefully you've turned OFF hyperthreading?

> gains can I expect on average from swapping from 4 disk raid 10 to 14 disk
> raid 10?  Could I expect to see 40 - 50% better throughput.

This is so dependant on application design that I can't possibly estimate.  
One big gain area for you will be moving the database log (pg_xlog) to its 
own private disk resource (such as a raid-1 pair).  In high-write 
enviroments, this can gain you 15% without changing anything else.

> The servers listed above are the dell 2650's which have perc 3
> controllers.  I have seen on this list where they are know for not
> performing well.  So any suggestions for an attached scsi device would be
> greatly appreciated.  Also, any thoughts on fibre channel storage devices?

The 2650s don't perform well in a whole assortment of ways.   This is why they 
are cheap.

NetApps seem to be the current best in NAS/SAN storage, although many people 
like EMC.   Stay away from Apple's XRaid, which is not designed for 
databases.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco

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