From mboxrd@z Thu Jan 1 00:00:00 1970
Return-Path: <gentoo-user+bounces-181162-garchives=archives.gentoo.org@lists.gentoo.org>
Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80])
(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
(No client certificate requested)
by finch.gentoo.org (Postfix) with ESMTPS id BA4A3139083
for <garchives@archives.gentoo.org>; Thu, 7 Dec 2017 00:29:16 +0000 (UTC)
Received: from pigeon.gentoo.org (localhost [127.0.0.1])
by pigeon.gentoo.org (Postfix) with SMTP id AE42FE0FD9;
Thu, 7 Dec 2017 00:29:11 +0000 (UTC)
Received: from mail-pg0-x22e.google.com (mail-pg0-x22e.google.com [IPv6:2607:f8b0:400e:c05::22e])
(using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
(No client certificate requested)
by pigeon.gentoo.org (Postfix) with ESMTPS id 3C576E0E97
for <gentoo-user@lists.gentoo.org>; Thu, 7 Dec 2017 00:29:11 +0000 (UTC)
Received: by mail-pg0-x22e.google.com with SMTP id g7so3197526pgs.0
for <gentoo-user@lists.gentoo.org>; Wed, 06 Dec 2017 16:29:11 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=gmail.com; s=20161025;
h=mime-version:sender:in-reply-to:references:from:date:message-id
:subject:to;
bh=Rx5SGJ4xfqh37cmjHtnagUsDjcVm4CamkouOIDfilX8=;
b=oyJdOLp7frA0ypH+UJXXw+4fFFCmDY5uaugVna2RDBR3Gv5glV4KHP/X08ZogTwmW9
XPZnyBHwoTEy2MnhQP8FVs7zhXzk5m0SPYgPeVNbxs0I8zEEpmNX0k58CNPVl/gDLAgj
ingURMEoiiBcgY/HnHup5qHG4cCo1+A+JeAM++kDVqfbXrIDQ4HegLMdH9WZ/0eJfAW7
TdjJDXrobXvD+/KvM6VGfEhrr5B1pM9vuEECDPzbMzQMt4b8uBt234G7vt6PBG/r7vFb
5W+Wucmf7DtiihaGLuSth6yNtbt/g2X0a5H9jbbLZULZgc1bDLN+r3/rC3wnmXLmB2dA
X/bw==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=1e100.net; s=20161025;
h=x-gm-message-state:mime-version:sender:in-reply-to:references:from
:date:message-id:subject:to;
bh=Rx5SGJ4xfqh37cmjHtnagUsDjcVm4CamkouOIDfilX8=;
b=j4cG1q9Zn8y2qs3Z5Rb7FWYAo2p61C3UAmgqKDWoOTS1fa+FhPUzzDHjgi7HvR3jxD
EBz5SV0iDIMvY3DaaKDDKk9QURpNapfMrEtFdIsKRx9sTP/KZ/HKWSoRqDVBiuPBn5AO
RZxzRuIcrGC69nNehzTIGXPv2nwT9FACRAy/JacWlNPteF5xUtE9JHgg7HdfEYNCMikM
UsllsDGby6g1prcgQUy7BMf4TzR2uih53yjxScErmsIVHB1rRTBRDqSiPByAnTLNq9LD
88J9nOhXmkTvfv7A0E5/lhv5jLCTLzPPCO4z18BSJgL8i1ELUA1nT2zIH4ZqKxhgxJ3n
Oj8g==
X-Gm-Message-State: AKGB3mJIAg7OeeCxTE8kCv5NdCRIMlA4bOAS9gKy4qIJSWiBD3XlzQ/Z
ZcBPsVPewiZFtmxP7CxAOAKQjBCnobMjF2LWYBerBw==
X-Google-Smtp-Source: AGs4zMbKNYeHDCFhWq5WbMx4f3PpI+eMgakaQXoX7EdjqGxwVugvFIdukqiwH9OvPq6pPoXltVG+WcBSwuj5PVzv0xk=
X-Received: by 10.99.171.69 with SMTP id k5mr12314034pgp.229.1512606549648;
Wed, 06 Dec 2017 16:29:09 -0800 (PST)
Precedence: bulk
List-Post: <mailto:gentoo-user@lists.gentoo.org>
List-Help: <mailto:gentoo-user+help@lists.gentoo.org>
List-Unsubscribe: <mailto:gentoo-user+unsubscribe@lists.gentoo.org>
List-Subscribe: <mailto:gentoo-user+subscribe@lists.gentoo.org>
List-Id: Gentoo Linux mail <gentoo-user.gentoo.org>
X-BeenThere: gentoo-user@lists.gentoo.org
Reply-to: gentoo-user@lists.gentoo.org
MIME-Version: 1.0
Sender: freemanrich@gmail.com
Received: by 10.100.151.169 with HTTP; Wed, 6 Dec 2017 16:29:08 -0800 (PST)
In-Reply-To: <20171207001328.GC5249@tp>
References: <ffe44495-92f4-c543-9aa4-51227cccc5c9@iinet.net.au>
<5A218A49.3050004@youngman.org.uk> <CAGfcS_mnXWDYPsTv9gHo-f+Gk_fD9zRm5izP1GsmOBq4c1pGTw@mail.gmail.com>
<20171206232829.GA5249@tp> <CAGfcS_k02c5Dsn1CJfQyNF5URRxYz1GYiAy+P_JoYnKeqdXs0w@mail.gmail.com>
<20171207001328.GC5249@tp>
From: Rich Freeman <rich0@gentoo.org>
Date: Wed, 6 Dec 2017 19:29:08 -0500
X-Google-Sender-Auth: wSFEdUHcL2YDSOkjw4o9fNxJAQw
Message-ID: <CAGfcS_=0rWL=GozRoJXXrY03Pb3TTaEe-drPgZe3PQydWkLY1w@mail.gmail.com>
Subject: Re: [gentoo-user] OT: btrfs raid 5/6
To: gentoo-user@lists.gentoo.org
Content-Type: text/plain; charset="UTF-8"
X-Archives-Salt: 72c4ec96-a023-4f4c-98c3-29df829c5963
X-Archives-Hash: 2b93f617ac8402e5ec4648dba70a8764
On Wed, Dec 6, 2017 at 7:13 PM, Frank Steinmetzger <Warp_7@gmx.de> wrote:
> On Wed, Dec 06, 2017 at 06:35:10PM -0500, Rich Freeman wrote:
>>
>> IMO the cost savings for parity RAID trumps everything unless money
>> just isn't a factor.
>
> Cost saving compared to what? In my four-bay-scenario, mirror and raidz2
> yield the same available space (I hope so).
>
Sure, if you only have 4 drives and run raid6/z2 then it is no more
efficient than mirroring. That said, it does provide more security
because raidz2 can tolerate the failure of any two disks, while
2xraid1 or raid10 can tolerate only half of the combinations of two
disks.
The increased efficiency of parity raid comes as you scale up.
They're equal at 4 disks. If you had 6 disks then raid6 holds 33%
more. If you have 8 then it holds 50% more. That and it takes away
the chance factor when you lose two disks. If you're really unlucky
with 4xraid1 the loss of two disks could result in the loss of 25% of
your data, while with an 8-disk raid6 the loss of two disks will never
result in the loss of any data. (Granted, a 4xraid1 could tolerate
the loss of 4 drives if you're very lucky - the luck factor is being
eliminated and that cuts both ways.)
If I had only 4 drives I probably wouldn't use raidz2. I might use
raid5/raidz1, or two mirrors. With mdadm I'd probably use raid5
knowing that I can easily reshape the array if I want to expand it
further.
--
Rich