On Sun, Mar 07, 2010 at 03:10:18AM -0500, Guy Watkins wrote:
quoted text
> } -----Original Message-----
> } From: Keld Simonsen [mailto:keld@keldix.com]
> } Sent: Sunday, March 07, 2010 3:07 AM
> } To: Neil Brown
> } Cc: Guy Watkins; 'Greg Freemyer'; 'Mark Knecht'; 'Linux-RAID'
> } Subject: Re: What RAID type and why?
> } 
> } 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
> 
> Are you sure RAID10 can loose 2 of 3 drives?  I did not think it worked that
> way.  I thought RAID10 maintained 2 copies, not 3.  But I have never used
> RAID10.

If you ask mdadm to do it, yes. Example:

mdadm --create /dev/md3 --chunk=256 -R -l 10 -n 3 -p f3 /dev/sd[abc]1

the "-p f3" is the one that asks to have 3 copies.

best regards
keld
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