Message-ID: <4E209908.8010500@agliodbs.com>
Date: Fri, 15 Jul 2011 12:46:16 -0700
From: Josh Berkus <josh@agliodbs.com>
Organization: PostgreSQL Experts Inc.
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To: pgsql-performance@postgresql.org
Subject: Re: Hardware advice for scalable warehouse db
References: <ivon1e$81d$1@dough.gmane.org>
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On 7/14/11 11:34 PM, chris wrote:
> Any comments on the configuration? Any experiences with iSCSI vs. Fibre
> Channel for SANs and PostgreSQL? If the SAN setup sucks, do you see a
> cheap alternative how to connect as many as 16 x 2TB disks as DAS?

Here's the problem with iSCSI: on gigabit ethernet, your maximum
possible throughput is 100mb/s, which means that your likely maximum
database throughput (for a seq scan or vacuum, for example) is 30mb/s.
That's about a third of what you can get with good internal RAID.

While multichannel iSCSI is possible, it's hard to configure, and
doesn't really allow you to spread a *single* request across multiple
channels.  So: go with fiber channel if you're using a SAN.

iSCSI also has horrible lag times, but you don't care about that so much
for DW.

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com