From owner-freebsd-questions@FreeBSD.ORG Sat Aug 2 15:58:57 2014 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id F344FC5E for ; Sat, 2 Aug 2014 15:58:56 +0000 (UTC) Received: from mail-qa0-f50.google.com (mail-qa0-f50.google.com [209.85.216.50]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id B0C6C2F04 for ; Sat, 2 Aug 2014 15:58:55 +0000 (UTC) Received: by mail-qa0-f50.google.com with SMTP id s7so5113342qap.23 for ; Sat, 02 Aug 2014 08:58:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:mime-version:content-type:from :in-reply-to:date:cc:content-transfer-encoding:message-id:references :to; bh=8awJx8or0gz8IJ5hcQPtTelo4QnGrZtiMItNKY1srZw=; b=X9MDp4rUcIiesGN7bs4jmMtMGg/S2RMECejAxF/geKYJMw9NTQGcchn0fwNVuMLa83 RedNSfVUy2YDGjRDKUDsKqaGSSolhE08XgLzTTBAXqv5ckMFQs1O4T4ie1S4eL3jHN9q fYHH0/0yN2N34fP1qjeOvAWJMcOjfu8X+iyz0C0k3zUUHMrQAGiVsvT/tDSc3O/sJy8P pYVQXtVlLRWH+FaG+TkyVi+0pSFVyxpfTSRZ/jiJMT53dGaeW+gwIygPYggx6wHjHm/e Tkmk5MdidJk43JKPNuyFIkKTLEadW9uEiNCFyTlMhcoGR5jzZj9LQ+Vh48K3DyPs7I9+ uLpg== X-Gm-Message-State: ALoCoQnQa/RkRYfTG7Ht3llVcgtG8HYBfGM1vHIZm8u4LpA3r7xY+pdrSSyd4xJ65Qt4VxEV/AnR X-Received: by 10.224.137.65 with SMTP id v1mr20300212qat.53.1406995129441; Sat, 02 Aug 2014 08:58:49 -0700 (PDT) Received: from [192.168.2.65] ([96.236.21.80]) by mx.google.com with ESMTPSA id n20sm21144730qar.38.2014.08.02.08.58.48 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 02 Aug 2014 08:58:48 -0700 (PDT) Subject: Re: gvinum raid5 vs. ZFS raidz Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=windows-1252 From: Paul Kraus In-Reply-To: Date: Sat, 2 Aug 2014 11:58:47 -0400 Content-Transfer-Encoding: quoted-printable Message-Id: <27521B45-98E0-4FDD-978F-83DA0CFA993E@kraus-haus.org> References: <201408020621.s726LsiA024208@sdf.org> To: Warren Block X-Mailer: Apple Mail (2.1878.6) Cc: Scott Bennett , freebsd-questions@freebsd.org X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 02 Aug 2014 15:58:57 -0000 On Aug 2, 2014, at 6:25, Warren Block wrote: > On Sat, 2 Aug 2014, Scott Bennett wrote: >> On Tue, 29 Jul 2014 12:01:36 -0400 Paul Kraus = >=20 >>> ZFS parity is handled slightly differently than for traditional = raid-5 (as well as the striping of data / parity blocks). So you cannot = just count on loosing 1, 2, or 3 drives worth of space to parity. See = Matt Ahren?s Blog entry here = http://blog.delphix.com/matt/2014/06/06/zfs-stripe-width/ for (probably) = more data on this than you want :-) And here = https://docs.google.com/a/delphix.com/spreadsheets/d/1tf4qx1aMJp8Lo_R6gpT6= 89wTjHv6CGVElrPqTA0w_ZY/edit?pli=3D1#gid=3D2126998674 is his spreadsheet = that relates space lost due to parity to number of drives in raidz vdev = and data block size (yes, the amount of space lost to parity caries with = data block, not configured filesystem block size!). There is a separate = tab for each of RAIDz1, RAIDz2, and RAIDz3. >>>=20 >> Anyway, using lynx(1), it is very hard to make any sense of the = spreadsheet. >=20 > Even with a graphic browser, let's say that spreadsheet is not a = paragon of clarity. Do NOT try to understand the spreadsheet on it=92s own, it is part of = the Blog entry. Read the blog and look at the spreadsheet as Matt refers = to it. > It's not clear what "block size in sectors" means in that context. = Filesystem blocks, presumably, but are sectors physical or virtual disk = blocks, 512 or 4K? What is that number when using a standard = configuration of a disk with 4K sectors and ashift=3D12? It could be 1, = or 8, or maybe something else. >=20 > As I read it, RAIDZ2 with five disks uses somewhere between 67% and = 40% of the data space for redundancy. The first seems unlikely, but I = can't tell. Better labels or rearrangement would help. >=20 > A second chart with no labels at all follows the first. It has only = the > power-of-two values in the "block size in sectors" column. A = restatement of the first one... but it's not clear why. Look at the names of the sheets in the document. They are referred to = back in the blog entry. -- Paul Kraus paul@kraus-haus.org