UFS partitioning

[Jerry McAllister]

On Thu, Dec 04, 2008 at 11:47:23AM +1000, Da Rock wrote:

> 
> 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?

Yes, as described above. 

> 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.

No.  Slicing and Partitioning take up negligible space.   Building
a file system on the disk/slice/partition takes up a chunk.  The 
most is taken up by an 8% (by default) reserve that is held back
for root use when a file system is built.

////jerry


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