From mboxrd@z Thu Jan 1 00:00:00 1970 From: Goswin von Brederlow Subject: Re: Why do I need 4 disks for a raid6? Date: Wed, 18 Mar 2009 15:08:56 +0100 Message-ID: <87wsam53ev.fsf@frosties.localdomain> References: <87ljr4hsk9.fsf@frosties.localdomain> <20090318121825.GL32416@skl-net.de> <49C0EA5F.9070901@vshift.com> <20090318123525.GK17185@skl-net.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <20090318123525.GK17185@skl-net.de> (Andre Noll's message of "Wed, 18 Mar 2009 13:35:25 +0100") Sender: linux-raid-owner@vger.kernel.org To: Andre Noll Cc: Ruslan Sivak , Goswin von Brederlow , linux-raid@vger.kernel.org List-Id: linux-raid.ids Andre Noll writes: > On 08:34, Ruslan Sivak wrote: > >> I would guess the reason is that it doesn't make sense. As mentioned, if >> you are going to create a 3 disk raid 6, it's essentially a raid1 over 3 >> disks, at which point you are better off with the raid-1. I don't think >> there's a raid controller that would let you set something like this up, I >> don't see why the softraid should. > > Well, Goswin mentioned some pretty good reasons I think. > > Andre > -- > The only person who always got his work done by Friday was Robinson Crusoe Raid6 is the only level that requires such "sanity". Here is another scenario: Say you have a 2 disk raid1 and now want to switch to 5 disk raid6. No problem, add 3 new disks, set up 1+2 disk raid6, pvmove the data (don't you love LVM?), stop the raid1, grow the raid6 to 5 disks. It is clear that 1+2 disk raid6 only makes sense as a transitory step but one that is usefull. MfG Goswin