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Date:      Mon, 25 Jan 2010 09:45:23 +0000
From:      Matthew Seaman <m.seaman@infracaninophile.co.uk>
To:        Andriy Gapon <avg@icyb.net.ua>
Cc:        Mark Andrews <marka@isc.org>, FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org>, freebsd-questions@freebsd.org, Robert Noland <rnoland@freebsd.org>
Subject:   Re: Loader, MBR and the boot process
Message-ID:  <4B5D6833.6050200@infracaninophile.co.uk>
In-Reply-To: <4B5D6207.9090105@icyb.net.ua>
References:  <cf9b1ee01001211957j43a9d6a9j3d1e29d19aebf418@mail.gmail.com>	<20100122041237.GA22312@gothschlampen.com>	<cf9b1ee01001212049u6cffd8abo9efa380a8efa9609@mail.gmail.com>	<cf9b1ee01001212102r70b88806m21b167a2aa833362@mail.gmail.com>	<20100124092947.B72039@starfire.mn.org>	<cf9b1ee01001240759j2476cf3es2babd8b32a90f9aa@mail.gmail.com>	<201001242057.o0OKvHUE089237@drugs.dv.isc.org>	<1264387282.2869.24.camel@balrog.2hip.net> <4B5D6207.9090105@icyb.net.ua>

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Andriy Gapon wrote:
> on 25/01/2010 04:41 Robert Noland said the following:
>> On Mon, 2010-01-25 at 07:57 +1100, Mark Andrews wrote:
>>>      offset  The offset of the start of the partition from the beginn=
ing of
>>>              the drive in sectors, or * to have bsdlabel calculate th=
e correct
>>>              offset to use (the end of the previous partition plus on=
e, ignor-
>>>              ing partition `c'.  For partition `c', * will be interpr=
eted as
>>>              an offset of 0.  The first partition should start at off=
set 16,
>>>              because the first 16 sectors are reserved for metadata.
>> Ok, now this has my attention... My gut feeling right now is that this=

>> is a bug in geom_part_bsd.  I don't understand why the label isn't
>> protected.  (Adding -b 16 when adding the swap partition fixes this)
>> Another project to goes on my list...
>>
>> If anyone knows why this is done like this... please share.
>=20
> I presume that this is for purely historic reasons.
>=20

I believe this has been known about since 5.x days:

   http://www.freebsd.org/cgi/query-pr.cgi?pr=3D72812

As far as I recall, sometime around 6.1-RELEASE this should have been
fixed.  It certainly seems to be the case that it is harmless to have=20
a plain swap partition start at offset 0, but anything else, like encrypt=
ed
swap or putting a filesystem there needs the 16 sector offset.

	Cheers,

	Matthew

--=20
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
                                                  Kent, CT11 9PW


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