Re: Postgresql 9.0.6 Raid 5 or not please help.

Hi,

In addition, when you have multiple hard drive, it needs to be considered to put a database cluster and wal files separately on different spindles (hard drives), because of different I/O charasteristics, in particular update intensive workload.

Generally speaking, having 4 disks, one RAID-1 pair for a database cluster and another RAID-1 pair for WAL files, would be fine.

--
NAGAYASU Satoshi <satoshi(dot)nagayasu(at)gmail(dot)com>

-----Original Message-----
From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Sender: pgsql-performance-owner(at)postgresql(dot)orgDate: Fri, 23 Dec 2011 00:05:31
To: tuanhoanganh<hatuan05(at)gmail(dot)com>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: [PERFORM] Postgresql 9.0.6 Raid 5 or not please help.

On Thu, Dec 22, 2011 at 11:18 PM, tuanhoanganh <hatuan05(at)gmail(dot)com> wrote:
> Thanks for your answer. But how performance between raid5 and one disk.

One disk will usually win, 2 disks (in a mirror) will definitely win.
RAID-5 has the highest overhead and the poorest performance,
especially if it's degraded (1 drive out) that simple mirroring
methods don't suffer from. But even in an undegraded state it is
usually the slowest method. RAID-10 is generally the fastest with
redundancy, and of course pure RAID-0 is fastest of all but has no
redundancy.

You should do some simple benchmarks with something like pgbench and
various configs to see for yourself. For extra bonus points, break a
mirror (2 disk -> 1 disk) and compare it to RAID-5 (3 disk -> 2 disk
degraded) for performance. The change in performance for a RAID-1 to
single disk degraded situation is usually reads are half as fast and
writes are just as fast. For RAID-5 expect to see it drop by a lot.