From owner-freebsd-questions@FreeBSD.ORG Tue Aug 26 15:14:11 2014 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 5983E5E3 for ; Tue, 26 Aug 2014 15:14:11 +0000 (UTC) Received: from sasl.smtp.pobox.com (sasl.smtp.pobox.com [208.72.237.25]) by mx1.freebsd.org (Postfix) with ESMTP id 1E5423273 for ; Tue, 26 Aug 2014 15:14:10 +0000 (UTC) Received: from sasl.smtp.pobox.com (unknown [127.0.0.1]) by pb-sasl0.pobox.com (Postfix) with ESMTP id 80C9C314B6; Tue, 26 Aug 2014 11:13:42 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=pobox.com; h=subject :mime-version:content-type:from:in-reply-to:date:cc:message-id :references:to; s=sasl; bh=OQzrEVJgt2wMXnNC5wPjjq1OmbU=; b=YrU+i 35wdYQbCeYIS6zZdaWC38yLuz2fegUqPjA6rWeu8LsCAsMs7AxmgJp8D9aPov3aM 5g+pQOdrdk176p5Otr6gzt8uL9LHkPOfrXf/gTH7tjSo/eS8iSfha2jRviMMmX/W TY4DQBdpvieLi9lY3vzt+6Cq2IB3yyy9wRd4gA= DomainKey-Signature: a=rsa-sha1; c=nofws; d=pobox.com; h=subject :mime-version:content-type:from:in-reply-to:date:cc:message-id :references:to; q=dns; s=sasl; b=ih3FBT/M//+4+OvrxZqjbMbgj7NdN4D HUMXc5WHRoe4I4Mb35CsgAmlBBzFXIHIqPOSkwPGBE8afFgFkcNpnwThWD8Dl+yz oCLhmhnVV+TVezlXowPcWG1N/ccXFJk6dX4zXcX1lfqiKy44AkhBUK4zntIuRFJt UFr2uKfriY8Y= Received: from pb-sasl0.int.icgroup.com (unknown [127.0.0.1]) by pb-sasl0.pobox.com (Postfix) with ESMTP id 755C8314B4; Tue, 26 Aug 2014 11:13:42 -0400 (EDT) Received: from [192.168.45.241] (unknown [80.229.153.31]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by pb-sasl0.pobox.com (Postfix) with ESMTPSA id 6DD9C314AE; Tue, 26 Aug 2014 11:13:29 -0400 (EDT) Subject: Re: some ZFS questions Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) From: Andrew McRae X-Priority: 5 In-Reply-To: Date: Tue, 26 Aug 2014 16:07:58 +0100 Message-Id: References: <201408070816.s778G9ug015988@sdf.org> <40AF5B49-80AF-4FE2-BA14-BFF86164EAA8@kraus-haus.org> <201408211007.s7LA7YGd002430@sdf.org> <201408241015.s7OAFRv7010196@sdf.org> <20140825014249.GA28995@neutralgood.org> To: Warren Block X-Mailer: Apple Mail (2.1878.6) X-Pobox-Relay-ID: 89ABACF0-2D33-11E4-9D90-7FB96395E023-05926501!pb-sasl0.pobox.com Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.18-1 Cc: Michael Sierchio , FreeBSD Questions X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Aug 2014 15:14:11 -0000 On 25 Aug 2014, at 04:23, Warren Block wrote: > On Sun, 24 Aug 2014, Michael Sierchio wrote: >=20 >> On Sun, Aug 24, 2014 at 8:00 PM, Warren Block = wrote: >>> On Sun, 24 Aug 2014, Michael Sierchio wrote: >>>=20 >>>> On Sun, Aug 24, 2014 at 6:42 PM, wrote: >>>>=20 >>>>=20 >>>>> If you can use GPT partitioning then you can have GPT labels on >>>>> partitions >>>>> spanning entire disks. Then you can rearrange physical disks to = your >>>>> hearts >>>>> content. >>>>>=20 >>>>> The bonus is that you can put identifying information in the label = name >>>>> to be even more sure you are replacing the correct disk when the = time >>>>> comes. >>>>=20 >>>>=20 >>>> You can do this - and it's the approach that FreeNAS takes, but you >>>> lose the benefits of presenting a whole disk to ZFS - the ability = to >>>> fully use the disk cache when presented a raw device rather than a >>>> partition. >>>=20 >>>=20 >>> I thought that was a Solaris-only limitation. In fact, I'm pretty = sure it >>> is, and does not apply on FreeBSD. >>=20 >> You mean Solaris-only benefit? >=20 > No, I mean that the disk cache problem was only on Solaris, and does = not apply to FreeBSD. On FreeBSD, there is no difference in performance = between partitions versus the whole disk. Actually the problem never existed in the first place. It=92s an urban = myth based on a misunderstanding of the fact that when presented with a = whole disk, ZFS tries to enable the disk=92s write cache. (And that = generally has no effect, except for some old Sun-branded disks that = shipped with the write cache disabled, as I understand it.) Here=92s the code, still in FreeBSD: = https://svnweb.freebsd.org/base/stable/10/sys/cddl/contrib/opensolaris/uts= /common/fs/zfs/vdev_disk.c?view=3Dmarkup#l569 Another comment: http://marc.info/?l=3Dzfs-discuss&m=3D134022989322125