From: Greg Smith <greg@2ndquadrant.com>
To: Anj Adu <fotographs@gmail.com>
Cc: pgsql-admin@postgresql.org
Subject: Re: more 10K disks or less 15K disks
Date: Thu, 29 Apr 2010 01:30:54 -0400
Message-ID: <4BD9198E.904@2ndquadrant.com> (raw)
In-Reply-To: <u2zf2fd819a1004282145wc60c3b39o7f0679fec9f607f8@mail.gmail.com>
References: <i2pf2fd819a1004281127sf91d988cua1d95d13d09dae09@mail.gmail.com>
<4BD8DCEA.2020003@2ndquadrant.com>
<u2zf2fd819a1004282145wc60c3b39o7f0679fec9f607f8@mail.gmail.com>
Anj Adu wrote:
> We do not archive the WALs. We use application-level replication to
> achieve redundancy. WAL archiving was difficult to support with the
> earlier hardware we had ( 6x300G 10K disks Dell 2850) given the
> volumes we were dealing with. The RAID card should be from the same
> manufacturer (LSI in Dell's case).
>
The database is generating WAL files that are written to the pg_xlog
directory. Sometimes this is broken out into a separate drive so that
it's possible to measure how much I/O is being written to there, as
opposed to the main database drive. That's the WAL writing I was asking
about, not the overhead of archiving WAL files to elsewhere. The way
that WAL writes go to disk, you can't always speed them up just by
throwing more disks at them--sometimes, you just need the individual
disk involved to be as fast as possible.
You should try to get the same Dell RAID controller you're already
using, that you know delivers good performance running your app. All
I've heard about the models released after the Perc 6i has been bad
news. Dell varies how much they tinker with the LSI firmware in their
own version of each card, and they didn't do very much of that in the
Perc 6 series. They seem to be changing around the newer models more
again, which is always bad news.
--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com www.2ndQuadrant.us
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To: pgsql-admin@postgresql.org
Cc: greg@2ndquadrant.com, fotographs@gmail.com
Subject: Re: more 10K disks or less 15K disks
In-Reply-To: <4BD9198E.904@2ndquadrant.com>
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