From: Brian Hurt <bhurt@janestcapital.com>
To: Bryan Murphy <bryan.murphy@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: SAN vs Internal Disks
Date: Fri, 07 Sep 2007 14:21:52 -0400
Message-ID: <46E196C0.5020508@janestcapital.com> (raw)
In-Reply-To: <bd8531800709071056g740cb44cld04cd489bc4e6343@mail.gmail.com>
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<dcc563d10709060925o6f11f632sbfbc2b64530ae80d@mail.gmail.com>
<a199704d0709061003u71d536fbh9d71ed095dfe16b@mail.gmail.com>
<Pine.GSO.4.64.0709062354040.28915@westnet.com>
<20070907100446.GE1795@mathom.us>
<20070907103341.GC20896@oppetid.no>
<46E18886.7060502@aptalaska.net>
<bd8531800709071056g740cb44cld04cd489bc4e6343@mail.gmail.com>
Bryan Murphy wrote:
>Our database server connects to the san via iSCSI over Gig/E using
>jumbo frames. File system is XFS (noatime).
>
>
>
>
...
>Throughput, however, kinda sucks. I just can't get the kind of
>throughput to it I was hoping to get. When our memory cache is blown,
>the database can be downright painful for the next few minutes as
>everything gets paged back into the cache.
>
>
>
Remember that Gig/E is bandwidth limited to about 100 Mbyte/sec. Maybe
a little faster than that downhill with a tailwind, but not much.
You're going to get much better bandwidth connecting to a local raid
card talking to local disks simply due to not having the ethernet as a
bottleneck. iSCSI is easy to set up and manage, but it's slow. This is
the big advantage Fibre Channel has- serious performance. You can have
multiple channels on a single fibre channel card- IIRC, QLogic's cards
have a default of 4 channels- each pumping 400 Mbyte/sec. At which
point the local bus rapidly becomes the bottleneck. Of course, this
comes at the cost of a signifigant increase in complexity.
Brian
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To: pgsql-performance@postgresql.org
Cc: bhurt@janestcapital.com, bryan.murphy@gmail.com
Subject: Re: SAN vs Internal Disks
In-Reply-To: <46E196C0.5020508@janestcapital.com>
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