From: "H. Peter Anvin" <hpa@zytor.com>
To: John Robinson <john.robinson@anonymous.org.uk>
Cc: David Brown <david.brown@hesbynett.no>, NeilBrown <neilb@suse.de>,
Oliver Martin <oliver@volatilevoid.net>,
linux-raid@vger.kernel.org
Subject: Re: Creating a 3-disk RAID6 array
Date: Fri, 18 May 2012 00:30:47 -0700 [thread overview]
Message-ID: <4FB5FAA7.4090401@zytor.com> (raw)
In-Reply-To: <4FB50573.6020604@anonymous.org.uk>
On 05/17/2012 07:04 AM, John Robinson wrote:
> On 17/05/2012 14:18, David Brown wrote:
> [...]
>> Theoretically, a 3-disk RAID6 is like a 2-disk RAID5 or a 1-disk RAID1 -
> [...]
>> I can't think of any good reason for it /not/ to support 3-disk
>> RAID6, as there is nothing in the algorithms to hinder it.
>
> I've a vague recollection of Peter Anvin saying the implementation is
> optimised in such a way that it won't work.
>
Yes, it would have required introducing some odd special cases. A
3-disk RAID-6 is bitwise identical to a 3-disk RAID-1, so if Neil wants
to he could add "instant reshaping" support in mdadm (add a disk to a
3-disk RAID-1 turning it into a 4-disk RAID-6; and similar for 2-disk
RAID-1 into 3-disk RAID-5.)
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2012-05-18 7:30 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-17 1:24 Creating a 3-disk RAID6 array Oliver Martin
2012-05-17 1:38 ` NeilBrown
2012-05-17 13:18 ` David Brown
2012-05-17 14:04 ` John Robinson
2012-05-18 7:24 ` David Brown
2012-05-18 7:30 ` H. Peter Anvin [this message]
2012-05-18 7:57 ` NeilBrown
2012-05-19 0:04 ` H. Peter Anvin
2012-05-17 21:02 ` Dan Williams
2012-05-17 23:27 ` Oliver Martin
2012-05-17 4:22 ` Bill Davidsen
2012-05-18 2:36 ` Stan Hoeppner
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