From owner-freebsd-questions@FreeBSD.ORG Sat May 18 13:08:38 2013 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 59F3BA39 for ; Sat, 18 May 2013 13:08:38 +0000 (UTC) (envelope-from paul@kraus-haus.org) Received: from mail-gg0-x230.google.com (mail-gg0-x230.google.com [IPv6:2607:f8b0:4002:c02::230]) by mx1.freebsd.org (Postfix) with ESMTP id 206A4D0 for ; Sat, 18 May 2013 13:08:38 +0000 (UTC) Received: by mail-gg0-f176.google.com with SMTP id b1so333500ggm.21 for ; Sat, 18 May 2013 06:08:37 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-received:subject:mime-version:content-type:from:in-reply-to:date :cc:content-transfer-encoding:message-id:references:to:x-mailer :x-gm-message-state; bh=LqYUrEDKbFgCXfDV4xR/bWMRxjb8EVifoKfaQmBlQ5w=; b=ieCKh0Mn8EzwJX27yCK11IJduJIMDBjqrMhL+a//ki6LNsMuRErrR8bRur2AgusIjV viPtGOJfF7zRWIiWC4gjXXeoDn+Kyu2YHxCzLVnxai4C8lpCt+NonwZoXizUwbxN+ia3 +kN9fM/Cg2whxYryrdcdLyy7w5PmpA51Nyui6IyN3wuYSlOfWDfTglWKzO65+/WBAQx2 /sd6XfXn2SPlhs86BXHzK7uW8zzwfa+zY3BKShfgM+t3razYQjF81apdw1pfby/oOJZa QQ4Km6exa/LviimCHYLCoMUpjO+1Tfk3hRV/r/di2T4iXR6Q1ILl0oKIAoLhzMK1W5rC UQBQ== X-Received: by 10.236.147.75 with SMTP id s51mr29842758yhj.33.1368880803892; Sat, 18 May 2013 05:40:03 -0700 (PDT) Received: from [192.168.2.66] ([96.236.21.119]) by mx.google.com with ESMTPSA id n15sm24641031yhi.2.2013.05.18.05.40.01 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 18 May 2013 05:40:02 -0700 (PDT) Subject: Re: ZFS install on a partition Mime-Version: 1.0 (Mac OS X Mail 6.3 \(1503\)) Content-Type: text/plain; charset=windows-1252 From: Paul Kraus In-Reply-To: <20130518044900.GA30652@neutralgood.org> Date: Sat, 18 May 2013 08:40:00 -0400 Content-Transfer-Encoding: quoted-printable Message-Id: <4F46D2E7-308C-45C9-B3A0-B2870E69AC19@kraus-haus.org> References: <5FB78660-EDA4-40DB-8A0D-B0DE23A0FB6C@kraus-haus.org> <20130518044900.GA30652@neutralgood.org> To: kpneal@pobox.com X-Mailer: Apple Mail (2.1503) X-Gm-Message-State: ALoCoQmj7UKFEs36AxwZwGuUCt1I7MPEbKg376Rtu4GQrbcUjWoS2dQ+weG1LSbcOvxue9CP9LfD Cc: Liste FreeBSD X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 18 May 2013 13:08:38 -0000 On May 18, 2013, at 12:49 AM, kpneal@pobox.com wrote: > On Fri, May 17, 2013 at 08:03:30PM -0400, Paul Kraus wrote: >> On May 17, 2013, at 6:24 PM, "bsd@todoo.biz" wrote: >>> 3. Should I avoid using ZFS since my system is not well tuned and It = would be asking for trouble to use ZFS in these conditions.=20 >>=20 >> No. One of the biggest benefits of ZFS is the end to end data = integrity. >> IF there is a silent fault in the HW RAID (it happens), ZFS will = detect >> the corrupt data and note it. If you had a mirror or other redundant = device, >> ZFS would then read the data from the *other* copy and rewrite the = bad >> block (or mark that physical block bad and use another). >=20 > I believe the "copies=3D2" and "copies=3D3" option exists to enable = ZFS to > self heal despite ZFS not being in charge of RAID. If ZFS only has a = single > LUN to work with, but the copies=3D2 or more option is set, then if = ZFS > detects an error it can still correct it. Yes, but =85. What the "copies=3D" parameter does is tell ZFS = to make that many copies of every block written on the top level device. = So if you set copies=3D2 and then write a 2MB file, it will take up 4MB = of space since ZFS will keep two copies of it. ZFS will attempt to put = them on different devices if it can, but there are no guarantees here. = If you have a single vdev stripe and you lose that one device, you = *will* lose all your data (assuming you did not have another backup copy = someplace else). On the other hand, if the single device develops some = bad blocks, with copies=3D2 you will *probably* not lose data as there = will be other copies of those disk blocks elsewhere to recover from. =46rom my experience on the ZFS Discuss lists, the place people = seem to use copies=3D are on laptops where they only have = one drive and copies=3D is better than no protection at all, = it is just not complete protection. > This option is a dataset option, is inheritable by child datasets, and = can > be changed at any time affecting data written after the change. To get = the > full benefit you'll therefore want to set the option before putting = data > into the relevant dataset. You can change it any time and it will only effect data written = from that point on. This can be useful if you have both high value data = band low value and you can control when each is written. For example, = you leave copies=3D1 for most of the time, then you want to save your = wedding photos, so you set copies=3D3 and write all the wedding photos, = you then set copies=3D1. You will have three copies of the wedding = photos and one copy of everything else. -- Paul Kraus Deputy Technical Director, LoneStarCon 3 Sound Coordinator, Schenectady Light Opera Company