Date: Tue, 15 Jan 2013 16:00:01 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: <201301151600.r0FG01GL037227@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 17:55:57 +0200 Their on-disk formats are identical. Even if RAID BIOS supports RAID0+1, there is no problem to handle it as RAID10 at the OS level. That gives better reliability without any downsides. I think there is much higher chance that inexperienced user will choose RAID0+1 by mistake, then experienced wish do to it on intentionally. Do you know any reason why RAID0+1 can't be handled as RAID10? On 15.01.2013 17:28, Allen Landsidel wrote: > 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. > -- Alexander Motin
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