From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keld Simonsen <keld@keldix.com>
Subject: Re: What RAID type and why?
Date: Sun, 7 Mar 2010 09:06:38 +0100
Message-ID: <20100307080638.GA30126@light.rap.dk>
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To: Neil Brown <neilb@suse.de>
Cc: Guy Watkins <linux-raid@watkins-home.com>, 'Greg Freemyer' <greg.freemyer@gmail.com>, 'Mark Knecht' <markknecht@gmail.com>, 'Linux-RAID' <linux-raid@vger.kernel.org>
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On Sun, Mar 07, 2010 at 01:21:13PM +1100, Neil Brown wrote:
> On Sat, 06 Mar 2010 18:17:44 -0500
> "Guy Watkins" <linux-raid@watkins-home.com> wrote:
> 
> > } 
> > } At a minimum I would build a 3-disk raid 6.  raid 6 does a lot of i/o
> > } which may be a problem.
> > 
> > If he only needs 3 drives I would recommend RAID1.  Can still loose 2 drives
> > and you don't have the RAID6 I/O overhead.
> > 
> 
> and as md/raid6 requires at least 4 drives, RAID1 is not just the best
> solution to survive two failures on a 3-device array, it is the only solution.

Raid10 can also do it.

raid1 is in many ways obsolete and you should rather use raid10,
which in my eyeys is just another way of doing the same conceptual thing
as raid1.

Best regards
keld