From: Mark Mielke <mark@mark.mielke.cc>
To: Fernando Hevia <fhevia@ip-tel.com.ar>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
Date: Wed, 26 Dec 2007 11:23:28 -0500
Message-ID: <47728000.4000709@mark.mielke.cc> (raw)
In-Reply-To: <0ea101c847d2$16f94bc0$8f01010a@iptel.com.ar>
References: <0ea101c847d2$16f94bc0$8f01010a@iptel.com.ar>
Fernando Hevia wrote:
>
> Database will be about 30 GB in size initially and growing 10 GB per
> year. Data is inserted overnight in two big tables and during the day
> mostly read-only queries are run. Parallelism is rare.
>
> I have read about different raid levels with Postgres but the advice
> found seems to apply on 8+ disks systems. With only four disks and
> performance in mind should I build a RAID 10 or RAID 5 array? Raid 0
> is overruled since redundancy is needed.
>
> I am going to use software Raid with Linux (Ubuntu Server 6.06).
>
In my experience, software RAID 5 is horrible. Write performance can
decrease below the speed of one disk on its own, and read performance
will not be significantly more than RAID 1+0 as the number of stripes
has only increased from 2 to 3, and if reading while writing, you will
not get 3X as RAID 5 write requires at least two disks to be involved. I
believe hardware RAID 5 is also horrible, but since the hardware hides
it from the application, a hardware RAID 5 user might not care.
Software RAID 1+0 works fine on Linux with 4 disks. This is the setup I
use for my personal server.
Cheers,
mark
--
Mark Mielke <mark@mielke.cc>
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To: pgsql-performance@postgresql.org
Cc: mark@mark.mielke.cc, fhevia@ip-tel.com.ar
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
In-Reply-To: <47728000.4000709@mark.mielke.cc>
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