From owner-freebsd-questions@FreeBSD.ORG Fri Jan 15 23:34:55 2010 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 4BB561065670 for ; Fri, 15 Jan 2010 23:34:55 +0000 (UTC) (envelope-from jmc-freebsd2@milibyte.co.uk) Received: from relay.pcl-ipout01.plus.net (relay.pcl-ipout01.plus.net [212.159.7.99]) by mx1.freebsd.org (Postfix) with ESMTP id DCC9C8FC0C for ; Fri, 15 Jan 2010 23:34:54 +0000 (UTC) X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: ApoEAOuKUEvUnw4R/2dsb2JhbADaGIQxBA Received: from pih-relay04.plus.net ([212.159.14.17]) by relay.pcl-ipout01.plus.net with ESMTP; 15 Jan 2010 23:34:53 +0000 Received: from [84.92.153.232] (helo=curlew.milibyte.co.uk) by pih-relay04.plus.net with esmtp (Exim) id 1NVvgr-00059M-AM for freebsd-questions@freebsd.org; Fri, 15 Jan 2010 23:34:53 +0000 Received: by curlew.milibyte.co.uk with local (Exim 4.71) (envelope-from ) id 1NVvgr-0003v5-0R for freebsd-questions@freebsd.org; Fri, 15 Jan 2010 23:34:53 +0000 From: Mike Clarke To: freebsd-questions@freebsd.org Date: Fri, 15 Jan 2010 23:34:52 +0000 User-Agent: KMail/1.9.10 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <201001152334.52978.jmc-freebsd2@milibyte.co.uk> X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: jmc-freebsd2@milibyte.co.uk X-SA-Exim-Scanned: No (on curlew.milibyte.co.uk); SAEximRunCond expanded to false X-Plusnet-Relay: ee70a69dd1e6d57d55636417dcdba4ff Subject: Newbie gmirror questions X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 Jan 2010 23:34:55 -0000 I'm about to upgrade to more disk space and I'm tempted use this as an opportunity to get two disks and implement gmirror. Before I go ahead there's a few aspects of mirroring I'm not sure about and would appreciate some advice. I'm using grub for multi booting. Does this introduce any problems if I want to boot into Windows or Linux on one of the other partitions? The gmirror manpage describes the procedure for handling kernel dumps using the prefer balance algorithm in the early stages of booting and then switching to round-robin in the /etc/rc.local script. It then goes on to say that "If on the next boot a component with a higher priority will be available, the prefer algorithm will choose to read from it and savecore(8) will find nothing". Does this only arise if I've made some change to the configuration of the mirror between the dump and the reboot or is there some instances when the priority automatically changes? Some of the articles I've read about gmirror suggest setting the balance to round-robin while others just leave this at the default setting of split. Am I right in assuming that round-robin would give better performance, and does it make much noticeable difference in real terms. In particular am I likely to see a reduction in performance using gmirror compared with what I would get with just a normal single disk. Finally, recent articles say to set kern.geom.debugflags to 17 when creating a mirror on a mounted drive while older articles say to set it to 16. Although I'll probably be creating the mirror on my disks before copying my system onto them so I don't really need to worry about setting this flag but I'm curious to know the difference between using the two values. -- Mike Clarke