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Date:      Tue, 24 May 2011 23:04:30 +0400
From:      "Andrey V. Elsukov" <ae@FreeBSD.org>
To:        Victor Balada Diaz <victor@bsdes.net>
Cc:        stable@freebsd.org
Subject:   Re: gpart usage
Message-ID:  <4DDC013E.5040107@FreeBSD.org>
In-Reply-To: <20110524172718.GG1291@equilibrium.bsdes.net>
References:  <20110524132028.GE1291@equilibrium.bsdes.net> <4DDBC4A9.7040404@FreeBSD.org> <20110524150951.GF1291@equilibrium.bsdes.net> <4DDBD73B.7090600@FreeBSD.org> <20110524172718.GG1291@equilibrium.bsdes.net>

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On 24.05.2011 21:27, Victor Balada Diaz wrote:
>>> So the 16 sector offset in BSD label is really needed or isn't?
>>
>> First 8 KBytes of the freebsd partition are reserved for the boot code=

>> (/boot/boot). The table of BSD partitions itself is located in the
>> second sector. So, if you plan to create freebsd-ufs partition you can=

>> create it without any offset. But if it will be not an UFS partition,
>> then i would created it with offset, otherwise you can wipe the BSD la=
bel.
>=20
> Who's the one reserving the 16 sector (8 KBytes) offset? the UFS filesy=
stem? the BSD slice/disklabel
> provider? the MBR provider?

BSD slice provider.

> If i understood it correctly, it would be like:
>=20
> Sector 0: usual IBM-PC MBR, MBR provider doesn't need anything more
> Sector 1-62: Reserved by MBR scheme (dunno why, but seems to be the cas=
e, probably CHS alignment) start: 63

Yes, currently we are actively discussing about this in the
freebsd-geom@ maillist.

> Sector 63: BSD scheme unused because on disk metadata is stored on seco=
nd sector

Here is saved the boot1 stage of /boot/boot.

> Sector 64: BSD scheme (disklabel) on disk data (148 + 8 * 16 =3D 276 by=
tes according to sys/disklabel.h)

GEOM_PART_BSD supports up to 20 partitions.

> Sectors 65-(63+16): Reserved by ??? for /boot/boot

Here is saved the boot2 stage of /boot/boot.

> Sectors (63+16)+: partitions

If you will not use offset for the first BSD partition, then you can
wipe BSD scheme with this command:
# dd if=3D/dev/zero of=3D/dev/da0s1a count=3D2

--=20
WBR, Andrey V. Elsukov


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