Date: Thu, 30 Oct 2008 09:48:17 -0700 From: Marcel Moolenaar <xcllnt@mac.com> To: John Baldwin <jhb@freebsd.org> Cc: Franck <royer.franck@gmail.com>, questions@freebsd.org Subject: Re: GPT Support on Freebsd Message-ID: <33E2BB19-64F9-42E2-89A6-034051390053@mac.com> In-Reply-To: <200810300936.05232.jhb@freebsd.org> References: <49059437.4000700@free.fr> <200810291754.07992.jhb@freebsd.org> <e8bd48970810291520w57a1c3bcjec7303ce213698fe@mail.gmail.com> <200810300936.05232.jhb@freebsd.org>
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On Oct 30, 2008, at 6:36 AM, John Baldwin wrote: > Ok, so it's not a PMBR. My understanding is that a GPT requires the > MBR to be > a PMBR (only one partition in the 4th slot with a special type of > 0xee that > covers the whole disk). What this box is doing is trying to make > the MBR > match the first 4 partitions in the GPT. I'm not sure if you will > be able to > get FreeBSD's GPT stuff to recognize that reliably. Marcel (cc'd) > might have > some ideas. In FreeBSD 6, the kernel checks explicitly for a PMBR when it checks for a GPT. Besides being part of the specification, it also avoids conflicts. In the GEOM framework, there's no a priori support for having one GEOM control another. When there's a valid MBR as well as a valid GPT, it's undeterministic which one will be used, unless they both cooperate. They don't. This is where GPart helps out. In FreeBSD 7 and up, GPart supports multiple partitioning schemes, including MBR and GPT. The kernel will not enforce a PMBR in front of a GPT, because upon detecting both a MBR and a GPT, the GPT will be used. However, this only applies when the kernel is configured with GEOM_PART_MBR and not with GEOM_MBR. At this time GEOM_MBR is still the default. So, to make it work for you, you need at least FreeBSD 7.1 (to be released shortly) or use next month's snapshot and build a custom kernel without GEOM_MBR and with GEOM_PART_MBR. In FreeBSD 8 and up GPart is the default and you won't have to make a custom kernel in that case. FYI, -- Marcel Moolenaar xcllnt@mac.com
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