From owner-freebsd-stable@FreeBSD.ORG Fri Mar 1 15:06:10 2013 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id E3F6D5D2 for ; Fri, 1 Mar 2013 15:06:10 +0000 (UTC) (envelope-from ronald-freebsd8@klop.yi.org) Received: from smarthost1.greenhost.nl (smarthost1.greenhost.nl [195.190.28.78]) by mx1.freebsd.org (Postfix) with ESMTP id 5E1D1247 for ; Fri, 1 Mar 2013 15:06:10 +0000 (UTC) Received: from smtp.greenhost.nl ([213.108.104.138]) by smarthost1.greenhost.nl with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.69) (envelope-from ) id 1UBRXD-0002dq-4K; Fri, 01 Mar 2013 16:06:07 +0100 Received: from [81.21.138.17] (helo=ronaldradial.versatec.local) by smtp.greenhost.nl with esmtpsa (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from ) id 1UBRXD-0006uo-1A; Fri, 01 Mar 2013 16:06:07 +0100 Content-Type: text/plain; charset=us-ascii; format=flowed; delsp=yes To: freebsd-stable@freebsd.org, "Karl Denninger" Subject: Re: Musings on ZFS Backup strategies References: <5130BA35.5060809@denninger.net> Date: Fri, 01 Mar 2013 16:06:05 +0100 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Ronald Klop" Message-ID: In-Reply-To: <5130BA35.5060809@denninger.net> User-Agent: Opera Mail/12.14 (Win32) X-Virus-Scanned: by clamav at smarthost1.samage.net X-Spam-Level: / X-Spam-Score: 0.8 X-Spam-Status: No, score=0.8 required=5.0 tests=BAYES_50 autolearn=disabled version=3.3.1 X-Scan-Signature: 9b84bad32751a42de3aa9e7877f1ca86 X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 01 Mar 2013 15:06:11 -0000 On Fri, 01 Mar 2013 15:24:53 +0100, Karl Denninger wrote: > Dabbling with ZFS now, and giving some thought to how to handle backup > strategies. > > ZFS' snapshot capabilities have forced me to re-think the way that I've > handled this. Previously near-line (and offline) backup was focused on > being able to handle both disasters (e.g. RAID adapter goes nuts and > scribbles on the entire contents of the array), a double-disk (or worse) > failure, or the obvious (e.g. fire, etc) along with the "aw crap, I just > rm -rf'd something I'd rather not!" > > ZFS makes snapshots very cheap, which means you can resolve the "aw > crap" situation without resorting to backups at all. This turns the > backup situation into a disaster recovery one. > > And that in turn seems to say that the ideal strategy looks more like: > > Take a base snapshot immediately and zfs send it to offline storage. > Take an incremental at some interval (appropriate for disaster recovery) > and zfs send THAT to stable storage. > > If I then restore the base and snapshot, I get back to where I was when > the latest snapshot was taken. I don't need to keep the incremental > snapshot for longer than it takes to zfs send it, so I can do: > > zfs snapshot pool/some-filesystem@unique-label > zfs send -i pool/some-filesystem@base pool/some-filesystem@unique-label > zfs destroy pool/some-filesystem@unique-label > > and that seems to work (and restore) just fine. > > Am I looking at this the right way here? Provided that the base backup > and incremental are both readable, it appears that I have the disaster > case covered, and the online snapshot increments and retention are > easily adjusted and cover the "oops" situations without having to resort > to the backups at all. > > This in turn means that keeping more than two incremental dumps offline > has little or no value; the second merely being taken to insure that > there is always at least one that has been written to completion without > error to apply on top of the base. That in turn makes the backup > storage requirement based only on entropy in the filesystem and not time > (where the "tower of Hanoi" style dump hierarchy imposed both a time AND > entropy cost on backup media.) > > Am I missing something here? > > (Yes, I know, I've been a ZFS resister.... ;-)) > I do the same. I only use zfs send -I (capital i) so I have all the snapshots on the backup also. That way the data survives an oops (rm -r) and a fire at the same time. :-) Ronald.