UFS partitioning

Da Rock rock_on_the_web at comcen.com.au
Wed Dec 3 17:46:33 PST 2008

On Tue, 2008-12-02 at 11:39 -0500, Jerry McAllister wrote:
> On Tue, Dec 02, 2008 at 11:17:40AM +0100, Polytropon wrote:
> > On Tue, 2 Dec 2008 10:56:44 +0100 (CET), Pieter Donche <Pieter.Donche at ua.ac.be> wrote:
> > > If FreeBSD is to put on the system as only operating system (Fdisk:
> > > "A = Use Entire disk"), then will the BSD-partitions will show up as
> > > ad0a (/), ad0b (swap), ad0d (/var) etc... correct or not (then what)?
> > 
> > You're mixing terminology here. :-) The "use entire disk" will
> > create a slice for FreeBSD covering the complete disk. A slice
> > is what MICROS~1 calls "primary partition".
> > 
> > Now the conclusion: Let's say you create a slice on ad0, it will
> > be ad0s1. Now you can create partitions inside this slice as you
> > mentioned it, e. g. ad0s1a = /, ad0s1b = swap, ad0s1d = /tmp,
> > ad0s1e = /var, ad0s1f = /usr and ad0s1g = /home. 
> True.   Too bad MS had to use the same terminology for slices
> as FreeBSD uses for subdivisions of slices.   But, it won't be
> undone now, so the confusion will continue.
> >  But if you're
> > refering to ad0a, ad0b, ad0d etc. you're stating that there's
> > no slice, implying that (if I see this correctly) it isn't possible
> > to boot from that disk. 
> It is correct that this would imply no slice being created.
> But it is not correct that it could not be bootable.  You can 
> use bsdlabel to write the boot sector to ad0 instead of ad0s1
> and it would be bootable - but would be what someone has enjoyed
> describing as a 'dangerously dedicated' disk.   FreeBSD can deal
> with it, but other systems cannot.
> I don't know if you can do this from sysinstall though.  I have 
> never tried.   But, it can be done by running bsdlabel by hand.
> >   Of couse, if you would intend to use
> > a (physical) second disk for only the home partition, you could
> > omit the slice and the partition and simply newfs ad1 - but
> > that wasn't your question.
> Probably the 'dangerously dedicated' disk is more often used this
> way as an additional (second) drive that is not made bootable.
> In that case, it is unlikely that one would mount any of the
> partitions on '/' making it the root filesystem.   That may
> be a problem.   But, otherwise this looks probable or more likely
> it would have some swap to add to the first disk and all the
> rest in either the a or d partitions mounted as something 
> like '/work' or /scratch'.
> > 
> >     ad0 |-----------------------------------------------| the whole disk
> >   ad0s1  \----------------------------------------------/ one slice
> >  ad0s1X   \--/\---/\-----/\-----/\-------/\------------/  partitions
> >             a   b     d      e       f           g
> >             /  swap  /tmp   /var    /usr       /home      mount point

Excuse my nose in here- I just have a couple of questions.

1) It IS possible to boot from a dedicated disk?

2) Does using dedicated mode increase the space available to use?
Partitioning normally takes up space so a HDD loses about 10% of usable
space doesn't it, so the space used by partitioning is can now be used
as filespace.

These questions are all theoretical: I've only read in passing about
dedicated mode, but the use of this would be highly specialised by

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