From owner-freebsd-hackers@FreeBSD.ORG Wed Jun 27 17:30:56 2012 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 3DABC106564A; Wed, 27 Jun 2012 17:30:56 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (bigknife-pt.tunnel.tserv9.chi1.ipv6.he.net [IPv6:2001:470:1f10:75::2]) by mx1.freebsd.org (Postfix) with ESMTP id 0FDAA8FC1D; Wed, 27 Jun 2012 17:30:56 +0000 (UTC) Received: from jhbbsd.localnet (unknown [209.249.190.124]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 7A613B94B; Wed, 27 Jun 2012 13:30:55 -0400 (EDT) From: John Baldwin To: Pawel Jakub Dawidek Date: Wed, 27 Jun 2012 10:26:02 -0400 User-Agent: KMail/1.13.5 (FreeBSD/8.2-CBSD-20110714-p17; KDE/4.5.5; amd64; ; ) References: <4FE9B01C.30306@yandex.ru> <201206270822.25672.jhb@freebsd.org> <20120627140817.GC1372@garage.freebsd.pl> In-Reply-To: <20120627140817.GC1372@garage.freebsd.pl> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Message-Id: <201206271026.02473.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Wed, 27 Jun 2012 13:30:55 -0400 (EDT) Cc: freebsd-hackers , "Andrey V. Elsukov" , Andriy Gapon , freebsd-current Subject: Re: [CFC/CFT] large changes in the loader(8) code X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Jun 2012 17:30:56 -0000 On Wednesday, June 27, 2012 10:08:17 am Pawel Jakub Dawidek wrote: > On Wed, Jun 27, 2012 at 08:22:25AM -0400, John Baldwin wrote: > > > I don't think so. Most common case is to configure partitions on top of > > > a mirror. Mirroring partitions is less common. Mostly because of > > > hardware RAIDs being popular. You don't expect hardware RAID vendor to > > > mirror partitions. Partition editors for other OS's won't work, but only > > > because they don't support gmirror. If they wouldn't recognize and > > > support some hardware (or pseudo-hardware) RAIDs there will be the same > > > problem. > > > > Hardware RAIDs hide the metadata from the disk that the BIOS (and disk > > editors) see. Thus, putting a GPT on a hardware RAID volume works fine > > as the logical volume is always seen by all OS's consistently. [...] > > Only if you won't connect this disk to a different controller. Yes, but people do not expect to be able to yank a hardware RAID drive out and hook it up to a "raw" disk controller and have it work. > > [...] The same > > is even true of the "software" RAID that graid supports since the metadata > > is defined by the vendor and thus the logical volume is always seen other > > OS's consistently. > > But is it seen without metadata by the boot loader? Yes. The logical volume shows up as a BIOS disk device. > What I'm trying to say is that it is fair to expect from the user to not > use gmirror-configured disk on different OS. If the user wants to use > this disk in different OS then he has to use format that is recognized > by both. > > Because gmirror is supported by FreeBSD we should improve the support by > teaching boot loader about it. Pretending gmirror is special and > recommending to mirror partitions with it instead of raw disks is not > the solution. > > I really can't see how gmirror is different in this regard from any > other software RAID or volume manager. If you try to use disk that > contains unrecognized metadata the behaviour is undefined (but hopefully > not a panic). It is not gmirror I am complaining about, it is the non-standard use of GPT. Note that gmirror + MBR works fine without violating what little standard there is for the MBR. Using a dedicated GPT partition to hold the gmirrror metadata would work with GPT (but be a good bit harder to work with in terms of GEOM I realize). But as I said, I won't object to these patches. -- John Baldwin