UFS partitioning

Jerry McAllister jerrymc at msu.edu
Tue Dec 2 08:44:30 PST 2008

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

Have fun,


> In case of "dual booting", you usually have more than one slice
> on your disk, but what happens inside the FreeBSD slice is mostly
> the same.
> > Page 427 of the FreeBSD handbook states that due to the use of 32-bit
> > integers to store the number of sectors is limited to 2^32 -1 
> > sectors/disk = 2 TB. A layout could be 

See my other message about this part.

> > a / 1Gb, 
> > b swap, 
> > d /root 20 Gb, (a /root partition is from an example of someone who
> > claims that at boot FreeBSD checks the partions in background except
> > for the / partition, by keeping / as small as possible, the time to
> > boot can be mimimized .. correct? but will /root ever be something
> > big ??)
> No no, / refers to "the root partition". One way of setting
> up püartitions is just to have one partition (one root parttion)
> and put everything on it, including /tmp, /var, /usr and /home.
> Another philosophy is to create partitions designated to their
> further use, just as I mentioned it above.
> For /, you would hardly need more than 1 GB. It just contains
> the kernel, basal system binaries, the configuration files and
> the directories that are mount points for all the other file
> systems. Even a 256 MB / partition should be enoung.
> > e /tmp 20 Gb, 
> > f /var 20 Gb, 
> > g /usr 20 Gb
> > this leaves 2420 Gb which is more than 2 Tb, so you can't put all 
> > that in 1 filesystem h /home, you will need to split that in 2
> > BSD-paritions, but since you can't have more that 8 BSD-partitions
> > (highest BSD-partition letter is h), you need to give up at least
> > one of d, e, f, g. ... correct or not (then what)?
> I quite doubt that FreeBSD's UFS 2 cannot handle a 2 TB partition
> as a whole, but because I don't have sch large disks with UFS
> (I have ZFS for them), I cannot tell.
> PS. Corrected subject (was missing).
> -- 
> Polytropon
> >From Magdeburg, Germany
> Happy FreeBSD user since 4.0
> Andra moi ennepe, Mousa, ...
> _______________________________________________
> freebsd-questions at freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-questions
> To unsubscribe, send any mail to "freebsd-questions-unsubscribe at freebsd.org"

More information about the freebsd-questions mailing list