From owner-freebsd-questions@FreeBSD.ORG Mon Jan 28 11:04:12 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 A8158506 for ; Mon, 28 Jan 2013 11:04:12 +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 4CB93B8D for ; Mon, 28 Jan 2013 11:04:11 +0000 (UTC) Received: from [31.186.37.179] (helo=smtp.marelmo.com) by uk1rly2283.eechost.net with esmtpa (Exim 4.72) (envelope-from ) id 1TzmVj-0004eg-16; Mon, 28 Jan 2013 11:04:33 +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 1TzmUq-00074h-UV; Mon, 28 Jan 2013 11:03:28 +0000 Date: Mon, 28 Jan 2013 11:03:05 +0000 From: Steve O'Hara-Smith To: Volodymyr Kostyrko Subject: Re: ZFS - whole disk or partition or BSD slice? Message-Id: <20130128110305.779e82e5c2c060be317216b6@sohara.org> In-Reply-To: <510647A5.2060804@gmail.com> References: <5105BEE4.4030402@mansionfamily.plus.com> <5105D611.4000506@ShaneWare.Biz> <20130128070324.08bc4d67f570835d75d90497@sohara.org> <510647A5.2060804@gmail.com> 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) Cc: freebsd-questions@freebsd.org 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 11:04:12 -0000 On Mon, 28 Jan 2013 11:40:53 +0200 Volodymyr Kostyrko wrote: > 28.01.2013 09:03, Steve O'Hara-Smith: > > 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. > > There's no need for that as ZFS can use same or bigger partition to > mirror existing one. If the second one would be smaller - do some math > and cut out some swap space. The problem arises when a drive fails, you order a replacement (go down the shop whatever) and when the new disc arrives and it's a few blocks smaller than the existing one. Then it cannot be used to mirror the existing one and you're in for a messy job to get a working mirror up. -- Steve O'Hara-Smith