bin/166589: atacontrol(8) incorrectly treats RAID10 and 0+1 the same

[Allen Landsidel]

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

From: Allen Landsidel <landsidel.allen at gmail.com>
To: Alexander Motin <mav at FreeBSD.org>
Cc: bug-followup at FreeBSD.org
Subject: Re: bin/166589: atacontrol(8) incorrectly treats RAID10 and 0+1 the
 same
Date: Tue, 15 Jan 2013 10:28:53 -0500

 Most devices typically only support one level or the other, but not 
 both.  I don't "Insist that it should exist", it *does* exist.  Both 
 levels do, and they are not the same thing.
 
 As for why it should be "available" to the user, I think that's a pretty 
 silly question.  If their hardware supports one or both levels, they 
 should be available to the user -- and called by their correct names.
 
 
 
 On 1/15/2013 03:12, Alexander Motin wrote:
 > 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.