pg.ddx.io  pgsql-performance@postgresql.org mailing list archive  

help / color / mirror / Atom feed
From: Mario Weilguni <roadrunner6@gmx.at>
To: pgsql-performance@postgresql.org
Subject: Re: Postgresql 9.0.6 Raid 5 or not please help.
Date: Fri, 23 Dec 2011 10:20:05 +0100
Message-ID: <4EF447C5.6050408@gmx.at> (raw)
In-Reply-To: <CAOR=d=0bh9QATnRpSDuBXALsDd5XcJAWTaH-BqQ8ECzxkc0Qhw@mail.gmail.com>
References: <CAJg-yaNFnhs9unUFvpUypoi-n6C9cja+yrJ+9muEGYkpuZQkgA@mail.gmail.com>
	<CAOR=d=0V9Xf3JRSaGzeRm274vGPXNgV2ur1UanEkd81QbpTjxg@mail.gmail.com>
	<CAOR=d=3geTWW=6sZQ-7dQDCdJGDmMsCfQsSoJ+Tyuks2_j9Bpg@mail.gmail.com>
	<CAJg-yaOXvs-G+vb=uKNbGGzC0vefXFP1XbsjE=tu3nKto4COQQ@mail.gmail.com>
	<CAOR=d=0bh9QATnRpSDuBXALsDd5XcJAWTaH-BqQ8ECzxkc0Qhw@mail.gmail.com>

Am 23.12.2011 08:05, schrieb Scott Marlowe:
> On Thu, Dec 22, 2011 at 11:18 PM, tuanhoanganh<hatuan05@gmail.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.
>
I'm not so confident that a RAID-1 will win over a single disk. When it 
comes to writes, the latency should be  ~50 higher (if both disk must 
sync), since the spindles are not running synchronously. This applies to 
softraid, not something like a battery-backend raid controller of course.

Or am I wrong here?






view thread (13+ messages)  latest in thread

Message-ID: <4EF447C5.6050408@gmx.at>
Permalink:  ../4EF447C5.6050408@gmx.at/
Also on:    postgresql.org/message-id/4EF447C5.6050408@gmx.at

 · 

reply
Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: pgsql-performance@postgresql.org
  Cc: roadrunner6@gmx.at
  Subject: Re: Postgresql 9.0.6 Raid 5 or not please help.
  In-Reply-To: <4EF447C5.6050408@gmx.at>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox