Date: Mon, 8 Mar 2010 12:38:12 -0600 From: Scot Hetzel <swhetzel@gmail.com> To: Pete French <petefrench@ticketswitch.com> Cc: xcllnt@mac.com, avg@icyb.net.ua, freebsd-geom@freebsd.org Subject: Re: another gpt vs mbr (sanity) check Message-ID: <790a9fff1003081038o317816dl9d5a274b63528df6@mail.gmail.com> In-Reply-To: <790a9fff1003081016q2b6a7d93qa55055aaaa9cf74@mail.gmail.com> References: <761C8533-B1DC-4DC7-8B2E-9CB1A8A5BEF8@mac.com> <E1Noh4B-000JjD-5u@dilbert.ticketswitch.com> <790a9fff1003081016q2b6a7d93qa55055aaaa9cf74@mail.gmail.com>
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On Mon, Mar 8, 2010 at 12:16 PM, Scot Hetzel <swhetzel@gmail.com> wrote: > On Mon, Mar 8, 2010 at 11:48 AM, Pete French > <petefrench@ticketswitch.com> wrote: >>> To clarify: the protective MBR is there only to protect the GPT >>> disk from tools that do not understand the GPT. Any GPT-aware >>> tool will treat the disk as a GPT disk. Consequently: the MBR >>> is inferior to the GPT... >> >> The queston is then, why isn't Windows treating it as GPT ? It's > > I have both MBR and GPT formated drives installed in my laptop, and > Windows 7 correctly identifies both drives. =A0The GPT drive was > formated using FreeBSD 8. > >> all very nice in theory, but if the practical upshot is that >> we get flash media which will read perfectly well in all operating >> systems except for BSD then thats not a good result, even if it >> is theoretically correct. Which is the situation the original poster >> appeared to have. >> > > The problem the original poster was having is this: > > Format drive as GPT > Re-Format drive as MBR > > FreeBSD still sees the drive as GPT instead of MBR. > > The reason is that FreeBSD is still detecting the Seconday GPT which > is located at the end of the disk, and using it due to the Primary GPT > was lost/corrupted when the drive was reformated as MBR disk. > > The real question is how was the drive reformated. =A0If it was > reformated using gpart: > > - Delete all existing partitions: > gpart delete -i X adY > - Destroy the GPT formated drive > gpart destroy adY > - Create the MBR formated drive > gpart create -s mbr adY > > And the secondary GPT header still exists, then it is a FreeBSD bug. I just had a look at the code for sys/geom/part/{g_part.c, g_part_gpt.c} and it does show that we delete the secondary GPT header when destroying a GPT formated drive. > But if it was reformated using a different tool, then it is a bug in > that tool for not reconizing that the original disk was formated as > GPT. > > Scot >
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