From: Greg Smith <gsmith@gregsmith.com>
To: Henrik <henke@mac.se>
Cc: pgsql-performance@postgresql.org
Subject: Re: Filesystem setup on new system
Date: Fri, 8 Aug 2008 18:42:05 -0400 (EDT)
Message-ID: <Pine.GSO.4.64.0808071213030.11658@westnet.com> (raw)
In-Reply-To: <D1169895-B311-4780-8CA6-C31314235224@mac.se>
References: <D1169895-B311-4780-8CA6-C31314235224@mac.se>
On Thu, 7 Aug 2008, Henrik wrote:
> My first idea was to have one partition on the RAID 10 using ext3 with
> data=writeback, noatime as mount options.
>
> But I wonder if I should have 2 partitions on the RAID 10 one for the PGDATA
> dir using ext3 and one partition for XLOGS using ext2.
Really depends on your write volume. The write cache on your controller
will keep having a separate xlog disk from being as important as it is
without one. If your write volume is really high though, it may still be
a bottleneck, and you may discover your app runs better with a dedicated
ext2 xlog disk instead.
The simple version is:
WAL write volume extremely high->dedicated xlog can be better
WAL volume low->more disks for the database array better even if that
mixes the WAL on there as well
If you want a true answer for which is better, you have to measure your
application running on this hardware.
> 6 SAS 15K drives in RAID 10 on one of the SAN controllers for database
With only 6 disks available, in general you won't be able to reach the WAL
as a bottleneck before being limited by seeks on the remaining 4 database
disks, so you might as well group all 6 together. It's possible your
particular application might prefer it the other way though, if you're
doing a while lot of small writes for example. I've seen a separate WAL
handle low-level benchmarks better, but on more real-world loads it's
harder to run into that situation.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
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To: pgsql-performance@postgresql.org
Cc: gsmith@gregsmith.com, henke@mac.se
Subject: Re: Filesystem setup on new system
In-Reply-To: <Pine.GSO.4.64.0808071213030.11658@westnet.com>
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