From owner-freebsd-current@FreeBSD.ORG Fri Jul 18 20:09:47 2008 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E99E71065694; Fri, 18 Jul 2008 20:09:47 +0000 (UTC) (envelope-from jonathan@onegoodidea.com) Received: from mailhost.significant-whitespace.com (mailhost.significant-whitespace.com [217.155.157.131]) by mx1.freebsd.org (Postfix) with ESMTP id A3C8E8FC1E; Fri, 18 Jul 2008 20:09:47 +0000 (UTC) (envelope-from jonathan@onegoodidea.com) Received: from [10.0.1.199] (wifi.significant-whitespace.com [217.155.157.133]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by mailhost.significant-whitespace.com (Postfix) with ESMTP id 6D0E87FC1F6; Fri, 18 Jul 2008 21:09:46 +0100 (BST) Message-Id: <439EEA62-06C6-4FF9-8848-2558574E6A75@onegoodidea.com> From: Jonathan Hogg To: Maurice Volaski In-Reply-To: Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes Content-Transfer-Encoding: 7bit Mime-Version: 1.0 (Apple Message framework v928.1) Date: Fri, 18 Jul 2008 21:09:45 +0100 References: X-Mailer: Apple Mail (2.928.1) Cc: freebsd-current@freebsd.org, pjd@FreeBSD.org Subject: Re: Would ZFS and gmirror work well together in a two-node failover cluster? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 18 Jul 2008 20:09:48 -0000 On 18 Jul 2008, at 19:16, Maurice Volaski wrote: > For one thing, how small can small window of data be, something > measured in minutes or hours? And this would be a system that could > be moving 100 MB+ per second, so the data could get outdated quickly. As I understand it (although I've not attempted this myself) there's no reason not to take snapshots at minute intervals or less - snapshots are pretty low cost. How far behind it gets depends on how much data you write to the main system and how fast you can sync it to the backup. The rough principal is that you take an initial snapshot and send/ receive that to the backup system. Then you take a second snapshot and send a "diff" stream to the backup. Then you can drop the initial snapshot and take a third and do the same. You drop the second, take a fourth, etc., etc. You have to avoid there being too many existent snapshots as the utilities become very slow when you have a lot. If you have a couple of spare machines, I'd give it a whirl and get some feeling for how well it works. > Plus, I'm looking for the failover to be automatic and near > instantaneous. That is, if I pull the power cord on the primary, > could the secondary go hot in under a minute? The ZFS filesystem(s) on the backup machine would be live at all times. You can even immediately start writing to them - though at that point you can't receive any more snapshots to the backup obviously. Failover of whatever systems were on top of these would be another question. Presumably this is a file server or something? Are you going to failover the IP address(es)? Jonathan