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Date:      Wed, 9 Dec 2009 23:48:47 +0100
From:      Polytropon <freebsd@edvax.de>
To:        James Phillips <anti_spam256@yahoo.ca>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Dangerously Dedicated (was: How do I create large ...)
Message-ID:  <20091209234847.042af7c0.freebsd@edvax.de>
In-Reply-To: <675083.74248.qm@web65510.mail.ac4.yahoo.com>
References:  <20091209002231.EB7D01065741@hub.freebsd.org> <675083.74248.qm@web65510.mail.ac4.yahoo.com>

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On Wed, 9 Dec 2009 11:42:31 -0800 (PST), James Phillips <anti_spam256@yahoo.ca> wrote:
> I sort of followed the discussion as well. There was some 
> disagreement about what "dangreously dedicated" means.

For comparison, I seem to remember that the two concepts
are called "compatibility mode" and "(dangerously) dedicated
mode", with the "dangerously" looking like a further
addition.



> Does it mean 
> getting rid of the DOS partition table (slices?) 

The use of slices - "DOS primary partitions" has often been
suggested for FreeBSD, but it has always worked without them.
I think the neccessarity to use them is what I said before:
compatibility. FreeBSD can handle "no slices" well, but
maybe other operating systems and "Windows" can't?

A common problem is that due do compatibility (again),
the number of slices is limited to 4.



> Or, does it mean 
> creating a slice or disks without BSD partitions?

How should this be possible? A partition (not a "DOS primary
partition", to avoid misunderstandings) is required for
creating a file system. Let's say you want to create a
file system on a disk:

	# newfs da0

This means that a partition is created - da0c - and inside
this partition the file system resides.

This is a common method for accessing data disks (disks
you don't boot from).



> The Handbook (18.3) 
> says: "If the disk is  going to be truly dedicated to FreeBSD, you 
> can use the dedicated mode. Otherwise, FreeBSD will have to live 
> within one of the PC BIOS partitions. FreeBSD calls the PC BIOS 
> partitions slices so as not to confuse them with traditional BSD 
> partitions." 

Exactly. No "dangerously" here.



> The programer in charge of the change seemed to indicate that the 
> "Dangerously dedicated" mode (I assume that means no BSD partititons) 
> conflicts with "GEOM: Modular Disk Transformation Framework."

No. It means "absence of a slice carrying the partitions",
which is the dedicated approach.



> GEOM 
> appears to be an asbtraction layer for accessing various disks. With 
> the move underway to start accessing all disk as SCSI(3 is device 
> independent (with translation help)) devices, it probably makes for 
> more elegant code. Handbook (19.2 GEOM Introduction) reads:
> "GEOM permits access and control to classes -- Master Boot Records, 
> BSD labels, etc -- through the use of providers, or the special files 
> in /dev. Supporting various software RAID configurations, GEOM will 
> transparently provide access to the operating system and operating 
> system utilities." 
> The important thing in that quote is that "BSD labels" (and Master 
> Boot Records) are mentioned specificly. 

That's correct. BSD labels, usually created by disklabel,
refer to FreeBSD partitions. MBR refers to slices (this
is "DOS primary partitions", and maybe includes "logical
volumes inside a DOS extended partition", all the things
that produce "drive letters").

The only thing I can conclude from this is that the removal
of dedicated mode is due to increasing compatibility with
the abilities of GEOM...

I've got lots of ? flying around my head... :-)

Allow me to try a summary:

Dedicated mode (also "dangerously dedicated mode"):

	da0  da0a   da0b   da0d   da0e   da0f   da0g
	{    (/)    (swap) (/tmp) (/var) (/usr) (/home)  }

Compatibility mode:

	da0  da0s1  da0s1a da0s1b da0s1d da0s1e da0s1f da0s1g
	{    [      (/)    (swap) (/tmp) (/var) (/usr) (/home)  ]  }

I'm not sure hgow this fits into the concept of installing
multiple operating systems. For example, "Windows" requires
you to install it in a slice. No problem with compatibility
mode, but does this work in dedicated mode, too? I think the
suggestion is "No, does not work" simply because the disk is
DEDICATED to FreeBSD.



-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...



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