From owner-freebsd-questions@FreeBSD.ORG Mon Jan 28 07:03:44 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 78DE01A6 for ; Mon, 28 Jan 2013 07:03:44 +0000 (UTC) (envelope-from ateve@sohara.org) Received: from uk1rly2283.eechost.net (relay01a.mail.uk1.eechost.net [217.69.40.75]) by mx1.freebsd.org (Postfix) with ESMTP id 245A4D4C for ; Mon, 28 Jan 2013 07:03:43 +0000 (UTC) Received: from [31.186.37.179] (helo=smtp.marelmo.com) by uk1rly2283.eechost.net with esmtpa (Exim 4.72) (envelope-from ) id 1TzilB-0002R8-Kv for freebsd-questions@freebsd.org; Mon, 28 Jan 2013 07:04:05 +0000 Received: from [192.168.63.1] (helo=steve.marelmo.com) by smtp.marelmo.com with smtp (Exim 4.80.1 (FreeBSD)) (envelope-from ) id 1Tzikn-00066i-E8 for freebsd-questions@freebsd.org; Mon, 28 Jan 2013 07:03:41 +0000 Date: Mon, 28 Jan 2013 07:03:24 +0000 From: Steve O'Hara-Smith To: freebsd-questions@freebsd.org Subject: Re: ZFS - whole disk or partition or BSD slice? Message-Id: <20130128070324.08bc4d67f570835d75d90497@sohara.org> In-Reply-To: References: <5105BEE4.4030402@mansionfamily.plus.com> <5105D611.4000506@ShaneWare.Biz> X-Mailer: Sylpheed 3.3.0 (GTK+ 2.24.6; amd64-portbld-freebsd9.1) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Auth-Info: 15567@permanet.ie (plain) 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: Mon, 28 Jan 2013 07:03:44 -0000 On Sun, 27 Jan 2013 22:05:05 -0800 Michael Sierchio wrote: > On Sun, Jan 27, 2013 at 5:36 PM, Shane Ambler > wrote: > > > I recall reading that using partitions for zfs on FreeBSD was as good as > > full disks. > > No, it isn't - ZFS can fully utilize disk caches when presented with > whole devices. There are possible reasons to create partitions - one > being that if an unfriendly OS sees the device, it won't try to > initialize it if it sees a partition map. Another is using a cheap > RAID controller that can't be fully disabled - in which case you > generally need to create a partition that doesn't include the last few > sectors of the disk, where such controllers keep magic data. There's one other good reason to use partitions when mirroring. When the time comes to replace a drive in a mirror it is necessary that the new drive be the same size (or larger) than the one it replaces. Given that drives of nominally the same capacity (and even of the same type and brand bought at different times) tend not to be exactly the same size using a partition a little smaller than the whole drive makes it certain that a replacement drive will be big enough to use in the mirror when it arrives. -- Steve O'Hara-Smith