From owner-freebsd-stable@freebsd.org Tue Nov 17 16:07:49 2015 Return-Path: Delivered-To: freebsd-stable@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id F1FCDA31067; Tue, 17 Nov 2015 16:07:48 +0000 (UTC) (envelope-from fjwcash@gmail.com) Received: from mail-oi0-x232.google.com (mail-oi0-x232.google.com [IPv6:2607:f8b0:4003:c06::232]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id B23F41BE1; Tue, 17 Nov 2015 16:07:48 +0000 (UTC) (envelope-from fjwcash@gmail.com) Received: by oige206 with SMTP id e206so7523395oig.2; Tue, 17 Nov 2015 08:07:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=jGimzqf72d8yTZww+w/pVpMX50a7lefVSCwrOX4Vv8Y=; b=WsU42+dyVzDatxadD1Cin2n+8iwHV75oAlezbagLLloRNqvjegSxiFzw07EbynV+Cg 3/5wBBgz8QeMcYqZ8Bzsdjg9RF2UYXxhuxO31+iVvxHYlza/6QjFYtWGp7BNoUqUNpDW PjgAFB0n5v6a3S4SLHsLB/u+2e6H4LSo9IybKfRQoufHmOvF7erv8Z2ZhdXzgbEppYfj CUAvtaj2veZ9TZGGn4llNKsZw4fKYN5jHXJVmNMiBxQnSD/fEGbQnr0b9Q6YwjukCP6E jTOuuYXL83Be/d3Nb9riq8upOfYpSSzwt4QNCTiiK2KDELpNUrhKWWG6S4nijuHuTKkU Osnw== MIME-Version: 1.0 X-Received: by 10.202.207.12 with SMTP id f12mr24682300oig.101.1447776467368; Tue, 17 Nov 2015 08:07:47 -0800 (PST) Received: by 10.76.29.74 with HTTP; Tue, 17 Nov 2015 08:07:47 -0800 (PST) In-Reply-To: <878D84A9-4553-413B-ACA4-5ABF499F28C1@punkt.de> References: <5644FF09.9090200@free.de> <56472686.5030301@free.de> <20151114143104.GA41119@in-addr.com> <7710CBCC-E68F-4454-9E29-E50ED1C6B511@sarenet.es> <20151116205734.GM48728@zxy.spb.ru> <878D84A9-4553-413B-ACA4-5ABF499F28C1@punkt.de> Date: Tue, 17 Nov 2015 08:07:47 -0800 Message-ID: Subject: Re: ZFS on labelled partitions (was: Re: LSI SAS2008 mps driver preferred firmware version) From: Freddie Cash To: "Patrick M. Hausen" Cc: freebsd-stable , freebsd-scsi@freebsd.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.20 X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 17 Nov 2015 16:07:49 -0000 On Tue, Nov 17, 2015 at 12:08 AM, Patrick M. Hausen wrote= : > Hi, all, > > > Am 16.11.2015 um 22:19 schrieb Freddie Cash : > > > > =E2=80=8BYou label the disks as they are added to the system the first = time. > That > > way, you always know where each disk is located, and you only deal with > the > > labels. > > we do the same for obvious reasons. But I always wonder about the possibl= e > downsides, because ZFS documentation explicitly states: > > ZFS operates on raw devices, so it is possible to create a storag= e > pool comprised of logical > volumes, either software or hardware. This configuration is not > recommended, as ZFS works > best when it uses raw physical devices. Using logical volumes > might sacrifice performance, > reliability, or both, and should be avoided. > > (from http://docs.oracle.com/cd/E19253-01/819-5461/gbcik/index.html) > > Can anyone shed some lght on why not using raw devices might sacrifice > performance or reliability? Or is this just outdated folklore? > =E2=80=8BOn Solaris, using raw devices allows ZFS to enable the caches on t= he disks themselves, while using any kind of partitioning on the disk forces the caches to be disabled. This is not an issue on FreeBSD due to the way GEOM works. Caches on disks are enabled regardless of how the disk is accessed (raw, dd-partitioned, MBR-partitioned, GPT-partitioned, gnop, geli, whatever). This is a common misconception and FAQ with ZFS on FreeBSD and one reason to not take any Sun/Oracle documentation at face value, as it doesn't always apply to FreeBSD. There were several posts from pjd@ about this back in the 7.x days when ZFS was first imported to FreeBSD. --=20 Freddie Cash fjwcash@gmail.com