From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f51.google.com ([74.125.82.51]:34675 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751205AbcATORs (ORCPT ); Wed, 20 Jan 2016 09:17:48 -0500 Received: by mail-wm0-f51.google.com with SMTP id u188so186562367wmu.1 for ; Wed, 20 Jan 2016 06:17:48 -0800 (PST) Received: from [10.3.28.25] ([155.210.218.230]) by smtp.gmail.com with ESMTPSA id q75sm25426182wmd.6.2016.01.20.06.17.46 for (version=TLSv1/SSLv3 cipher=OTHER); Wed, 20 Jan 2016 06:17:46 -0800 (PST) Subject: Re: raid1 vs raid5 To: Btrfs BTRFS References: <568BEE3F.4060402@gmail.com> From: Psalle Message-ID: <569F9709.4090608@gmail.com> Date: Wed, 20 Jan 2016 15:17:45 +0100 MIME-Version: 1.0 In-Reply-To: <568BEE3F.4060402@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: I had forgotten about this post and on rethinking about it I realized the kind of brain fart I was having. So thanks for the merciful silence ;-) On 05/01/16 17:24, Psalle wrote: > Hello all and excuse me if this is a silly question. I looked around > in the wiki and list archives but couldn't find any in-depth > discussion about this: > > I just realized that, since raid1 in btrfs is special (meaning only > two copies in different devices), the effect in terms of resilience > achieved with raid1 and raid5 are the same: you can lose one drive and > not lose data. > > So!, presuming that raid5 were at the same level of maturity, what > would be the pros/cons of each mode? > > As a corollary, I guess that if raid1 is considered a good compromise, > then functional equivalents to raid6 and beyond could simply be > implemented as "storing n copies in different devices", dropping any > complex parity computations and making this mode entirely generic. > Since this seems pretty obvious, I'd welcome your insights on what are > the things I'm missing, since it doesn't exist (and it isn't planned > to be this way, AFAIK). I can foresee consistency difficulties, but > that seems hardly insurmountable if its being done for raid1? > > Thanks in advance, > Psalle.