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Date:      Tue, 15 Jan 2013 08:20:01 GMT
From:      Alexander Motin <mav@FreeBSD.org>
To:        freebsd-bugs@FreeBSD.org
Subject:   Re: bin/166589: atacontrol(8) incorrectly treats RAID10 and 0+1 the same
Message-ID:  <201301150820.r0F8K1aD027442@freefall.freebsd.org>

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The following reply was made to PR bin/166589; it has been noted by GNATS.

From: Alexander Motin <mav@FreeBSD.org>
To: Allen Landsidel <landsidel.allen@gmail.com>
Cc: bug-followup@FreeBSD.org
Subject: Re: bin/166589: atacontrol(8) incorrectly treats RAID10 and 0+1 the
 same
Date: Tue, 15 Jan 2013 10:12:14 +0200

 That is clear and I had guess you mean it, but why do you insist that
 such RAID0+1 variant should even exist if it has no benefits over
 RAID10, and why it should be explicitly available to user?
 
 On 15.01.2013 04:51, Allen Landsidel wrote:
 > They are not variants in terminology, they are different raid levels. 
 > Raid0+1 is two RAID-0 arrays, mirrored into a RAID-1.  if one of the
 > disks fails, that entire RAID-0 is offline and must be rebuilt, and all
 > redundancy is lost.  A RAID-10 is composed of N raid-1 disks combined
 > into a RAID-0.  If one disk fails, only that particular RAID-1 is
 > degraded, and the redundancy of the others is maintained.
 > 
 > 0+1 cannot survive two failed disks no matter how many are in the
 > array.  10 can survive half the disks failing, if it's the right half.
 > 
 > This is something people who've never used more than 4 disks fail to
 > grasp, but those of us with 6 (or many many more) know very well.
 > 
 > On 1/14/2013 21:46, Alexander Motin wrote:
 >> There could be variants in terminology, but in fact for most of users
 >> they are the same. If you have opinion why they should be treated
 >> differently, please explain it.
 
 -- 
 Alexander Motin



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