From owner-freebsd-stable@FreeBSD.ORG Thu Jul 22 12:50:14 2010 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id C3BE01065673 for ; Thu, 22 Jul 2010 12:50:14 +0000 (UTC) (envelope-from paul@gromit.dlib.vt.edu) Received: from lennier.cc.vt.edu (lennier.cc.vt.edu [198.82.162.213]) by mx1.freebsd.org (Postfix) with ESMTP id 758D88FC08 for ; Thu, 22 Jul 2010 12:50:14 +0000 (UTC) Received: from zidane.cc.vt.edu (zidane.cc.vt.edu [198.82.163.227]) by lennier.cc.vt.edu (8.13.8/8.13.8) with ESMTP id o6MCnSxT007747; Thu, 22 Jul 2010 08:49:43 -0400 Received: from auth3.smtp.vt.edu (EHLO auth3.smtp.vt.edu) ([198.82.161.152]) by zidane.cc.vt.edu (MOS 4.1.8-GA FastPath queued) with ESMTP id JQE01492; Thu, 22 Jul 2010 08:49:43 -0400 (EDT) Received: from gromit.tower.lib.vt.edu (gromit.tower.lib.vt.edu [128.173.51.22]) (authenticated bits=0) by auth3.smtp.vt.edu (8.13.8/8.13.8) with ESMTP id o6MCngDA005619 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=NO); Thu, 22 Jul 2010 08:49:43 -0400 Mime-Version: 1.0 (Apple Message framework v1081) Content-Type: text/plain; charset=us-ascii From: Paul Mather In-Reply-To: <4C47B57F.5020309@langille.org> Date: Thu, 22 Jul 2010 08:49:42 -0400 Content-Transfer-Encoding: quoted-printable Message-Id: <5A35E293-87C2-4E96-863F-1734B2ECA796@gromit.dlib.vt.edu> References: <4C47B57F.5020309@langille.org> To: Dan Langille X-Mailer: Apple Mail (2.1081) X-Mirapoint-Received-SPF: 198.82.161.152 auth3.smtp.vt.edu paul@gromit.dlib.vt.edu 5 none X-Mirapoint-IP-Reputation: reputation=neutral-1, source=Fixed, refid=n/a, actions=MAILHURDLE SPF TAG X-Junkmail-Status: score=10/50, host=zidane.cc.vt.edu X-Junkmail-SD-Raw: score=unknown, refid=str=0001.0A020207.4C483E67.0111,ss=1,fgs=0, ip=0.0.0.0, so=2009-09-22 00:05:22, dmn=2009-09-10 00:05:08, mode=single engine X-Junkmail-IWF: false Cc: freebsd-stable Subject: Re: Using GTP and glabel for ZFS arrays X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 22 Jul 2010 12:50:14 -0000 On Jul 21, 2010, at 11:05 PM, Dan Langille wrote: > I hope my terminology is correct.... >=20 > I have a ZFS array which uses raw devices. I'd rather it use glabel = and supply the GEOM devices to ZFS instead. In addition, I'll also = partition the HDD to avoid using the entire HDD: leave a little bit of = space at the start and end. >=20 > Why use glabel? >=20 > * So ZFS can find and use the correct HDD should the HDD device ever > get renumbered for whatever reason. e.g. /dev/da0 becomes /dev/da6 > when you move it to another controller. I have created ZFS pools using this strategy. However, about a year ago = I still fell foul of the drive shuffling problem, when GEOM labels = appeared not to be detected properly: = http://lists.freebsd.org/pipermail/freebsd-geom/2009-July/003654.html This was using RELENG_7, and the problem was provoked by external USB = drives. The same issue might not occur with FreeBSD 8.x, but I thought I'd point = out my experience as a possible warning about using glabel. Nowadays, I use GPT labels ("gpart ... -l somelabel", referenced via = /dev/gpt/somelabel). > Why use partitions? >=20 > * Primarily: two HDD of a given size, say 2TB, do not always provide > the same amount of available space. If you use a slightly smaller > partition instead of the entire physical HDD, you're much more > likely to have a happier experience when it comes time to replace an > HDD. >=20 > * There seems to be a consensus amongst some that leaving the start = and > and of your HDD empty. Give the rest to ZFS. You should also try and accommodate 4K sector size drives these days. = Apparently, the performance boosts from hitting 4K-aligned sectors can = be very good. Cheers, Paul.=