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Re: [ADMIN] H/W RAID 5 on slower disks versus no raid on

From: "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>
To: Bjoern Metzdorf <bm(at)turtle-entertainment(dot)de>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: [ADMIN] H/W RAID 5 on slower disks versus no raid on
Date: 2002-11-21 21:24:00
Message-ID: Pine.LNX.4.33.0211211420280.23775-100000@css120.ihs.com (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-performance
On Thu, 21 Nov 2002, Bjoern Metzdorf wrote:

> > In fact, the linux kernel supports >2 drives in a mirror.  Useful for a 
> > mostly read database that needs to handle lots of concurrent users.
> 
> Good to know.
> 
> What do you think is faster: 3 drives in raid 1 or 3 drives in raid 5?

Generally RAID 5.  RAID 1 is only faster if you are doing a lot of 
parellel reads.  I.e. you have something like 10 agents reading at the 
same time.  RAID 5 also works better under parallel load than a single 
drive.

The fastest of course, is multidrive RAID0.  But there's no redundancy.

Oddly, my testing doesn't show any appreciable performance increase in 
linux by layering RAID5 or 1 over RAID0 or vice versa, something that 
is usually faster under most setups.


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