On Sun, 10 Dec 2000, Daniel C. Sobral wrote:

> Poul-Henning Kamp wrote:
> > 
> > >>| Partition table | Data                                            |
> > >>                  | Slice 1           | Slice 2 | Slice 3 | Slice 4 |
> > >>                  | Disklabel | Data  |
> > >>                              |   c   |
> > >>                              |a|b|f|g|
> > >
> > >That is really an excellent diagram.  That should be in an FAQ
> > >somewhere.  Doc committers?
> > 
> > Except it is not actually correct.  The BSD disklabel is usually
> > inside the 'a' partition and certainly inside the 'c'
> Is that so? Mea culpa, then. At least I knew what I was talking about
> wrt partition table and the actual slices.
> This diagram is just an example. There can be less slices, it doesn't
> show extended partitions (extended slices??? :),

This leaves out the most interesting (complicated) part.  FreeBSD supports
the fully recursive version of them:

Slice := OrdinarySlice or ExtendedSlice
OrdinarySlice := LabeledSlice or UnlabeledSlice (see above for layouts)

Layout of ExtendedSlice:
| ExtendedSlice                                   |
| Partition table | Slice | Slice | Slice | Slice |

The recursion gives a quaternary tree with OrdinarySlices as leaves.

For compatibility with other OS's (ones whose fdisk program actually
supports creating the tree :-), the full tree must not be used.  There
must be at most ExtendedSlice at each level, and at most one nonempty
OrdinarySlice except at the top level where there may be up to 4
OrdinarySlices.  The tree thus reduces to a list with up to 3 warts
at the top.

> it suggests an ordering
> that is not necessary. If this is going to the FAQ or the handbook, a
> number of notes should be made to point out these (and possibly others
> I'm overlooking right now) issues.

Other things not shown in the diagram:
- there may be more partitions (d|e|h).
- slice and partition order may be non-physical.
- slices may overlap the partition table in dubious configurations, including
  the "Dangerously Dedicated" one.
- slices may overlap each other in dubious configurations.  I sometimes use
  this feature to help move slices.
- partitions may overlap each other (... similarly).


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