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Re: [OT] RAID controllers blocking one another?

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: Sean Davis <sdavis2(at)mail(dot)nih(dot)gov>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: [OT] RAID controllers blocking one another?
Date: 2008-01-18 19:14:31
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Fri, 18 Jan 2008, Sean Davis wrote:

> FYI, here are the specs on the server.

Now we're getting somewhere.  I'll dump this on-list as it's a good 
example of how to fight this class of performance problems.

The usual troubleshooting procedure is to figure out how the motherboard 
is mapping all the I/O internally and then try to move things out of the 
same path.  That tells us that you have an Intel S5000PSL motherboard, and 
the tech specs are at

What you want to stare at is the block diagram that's Figure 10, page 27 
(usually this isn't in the motherboard documentation, and instead you have 
to drill down into the chipset documentation to find it).  Slots 5 and 6 
that have PCI Express x16 connectors (but run at x8 speed) both go 
straight into the memory hub.  Slots 3 and 4, which are x8 but run at x4 
speed, go through the I/O controller first.  Those should be slower, so if 
you put a card into there it will have a degraded top-end performance 
compared to slots 5/6.

Line that up with the layout in Figure 2, page 17, and you should be able 
to get an idea what the possibilities are for moving the cards around and 
what the trade-offs involved are.  Ideally you'd want both 3Ware cards to 
be in slots 5+6, but if that's your current configuration you could try 
moving the less important of the two (maybe the one with less drives) to 
either slot 3/4 and see if the contention you're seeing drops.

* Greg Smith gsmith(at)gregsmith(dot)com Baltimore, MD

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