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Date:      Thu, 10 Dec 2009 00:04:28 -0800 (PST)
From:      James Phillips <anti_spam256@yahoo.ca>
To:        freebsd-questions@freebsd.org
Subject:   Re: Dangerously Dedicated
Message-ID:  <291716.23061.qm@web65514.mail.ac4.yahoo.com>
In-Reply-To: <20091210043133.3AF5110656DC@hub.freebsd.org>

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> Date: Thu, 10 Dec 2009 03:12:45 +0100
> From: Polytropon <freebsd@edvax.de>
> Subject: Re: Dangerously Dedicated
> To: Maxim Khitrov <mkhitrov@gmail.com>
> Cc: freebsd-questions@freebsd.org
> Message-ID: <20091210031245.3fd58187.freebsd@edvax.de>
> Content-Type: text/plain; charset=3DUS-ASCII
>=20
> On Wed, 9 Dec 2009 20:41:40 -0500, Maxim Khitrov=20
<mkhitrov@gmail.com> > wrote:
> > On Wed, Dec 9, 2009 at 8:33 PM, Rolf Nielsen
> > <listreader@lazlarlyricon.com>
> wrote:
> > > As far as I understand it, it's called
> Dangerously Dedicated because it may
> > > cause other systems not to recognise the disk.
> Consequently, newfs'ing a
> > > slice without first partitioning it can hardly be
> DD, since that is what
> > > other systems do, right?

I think I understand: using the DOS compatible partition (slice)=20
table follows the principle of "least surprise." That is why I use=20
"slices" for my dedicated BSD machine. 4 places to put your data are=20
ostensibly better than 1, and I avoid any possible BIOS bugs if the=20
BIOS sees a "non-standard" MBR.=20

> >=20
> > That is correct. That slice will not be bootable, but
> you can use it
> > to store data.
>=20
> Being bootable is a matter of what the MBR boot block
> says. In a DD setting, it refers to the first partition
> (that's not within a slice), e. g. ad0a. Especially in
> a multi-OS setting, the use of slices seems to be
> strongly recommended so all operating systems behave
> in the required way (due to compatibility reasons,
> see "DOS primary partitions"), which limits the number
> of slices to 4.

I would say a common partition format is REQUIRED in a multi-boot=20
situation. For PC OS's, that means DOS compatibility.

=20
> For plain storage, it's not needed to encapsulate the
> partition with the file system inside a slice, e. g.
>=20
> =C2=A0=C2=A0=C2=A0 ad1=C2=A0 ad1s1=C2=A0 ad1s1e
> =C2=A0=C2=A0=C2=A0 {=C2=A0 =C2=A0 [=C2=A0 =C2=A0 =C2=A0
> (/data)=C2=A0 ]=C2=A0 }
>=20
> in comparison to
>=20
> =C2=A0=C2=A0=C2=A0 ad1=C2=A0 ad1c
> =C2=A0=C2=A0=C2=A0 {=C2=A0 =C2=A0 (/data)=C2=A0 }
>=20
> And as it is known, the "c" can be omitted, as in
>=20
> =C2=A0=C2=A0=C2=A0 # mount /dev/ad1 /data
>=20
>=20

The Detailed 8.0 release notes don't say anything about bootability:
        2.2.5 File Systems
          =E2=80=9Cdangerously dedicated=E2=80=9D mode for the UFS file sys=
tem=20
        is no longer supported
 http://www.freebsd.org/releases/8.0R/relnotes-detailed.html

I also note that the DOS partition (slice) table is not explictly=20
required either: could you use an Apple partiton (slice) table=20
instead?=20
UFS not supporting DD mode struck me as weird BECAUSE it has to work=20
with different architectures.=20
Of course, if you are just storing raw data, you don't always *need*=20
a filesystem.=20

Regards,

James Phillips=0A=0A=0A      ______________________________________________=
____________________=0AYahoo! Canada Toolbar: Search from anywhere on the w=
eb, and bookmark your favourite sites. Download it now=0Ahttp://ca.toolbar.=
yahoo.com.



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