8.0-RELEASE and "dangerously dedicated" disks

[Bob Johnson]

On 11/28/09, Peggy Wilkins <enlil65 at gmail.com> wrote:
> Can someone elaborate on what exactly this statement in the 8.0
> detailed release notes means?
>
> http://www.freebsd.org/releases/8.0R/relnotes-detailed.html#FS
>
>> 2.2.5 File Systems
>>
>> “dangerously dedicated” mode for the UFS file system is no longer
>> supported.
>>
>>  Important: Such disks will need to be reformatted to work with this
>> release.
>
[...snip...]
>
> It doesn't make sense to me that "dangerously dedicated" could have an
> impact on UFS filesystems specifically.  A partition table is just a
> partition table, regardless of what filesystems might be written on
> disks, yes?  Am I misunderstanding something here?
>

Unless someone has changed the meaning of the term in the last few
years, a "dangerously dedicated" disk is one that has the FreeBSD file
system on it with no partition table. It is basically an artifact of
the pre-Microsoft origin of BSD (there were reasons it stayed around,
but they ought to be ancient history by now). Since UFS is the
standard FreeBSD filesystem, DD disks contain UFS filesystems almost
by definition.

So, to get to the main point of your confusion (and unless I am the
one that is very confused), "dangerously dedicated" disks do not have
partition tables. That's what makes them dangerous. It confuses things
that expect to find a partition table.

If your partition name has an "s" (slice number) in it (e.g. ad2s1a)
it is not "dangerously dedicated". A "DD" disk partition would have a
name like "ad2a" with no slice number. At least, that's the way it
used to be. I quit using DD disks years ago when it became clear to me
that the unintended side effects aren't worth the few bytes you save.
Every once in a while a BIOS, or a utility, or something else pops up
that expects to find a partition table and gets confused without it.
It appears that it has happened again.

> Thanks for helping to clear up my confusion...

I hope I helped.

-- 
-- Bob Johnson
   fbsdlists at gmail.com