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Date: Wed, 2 Sep 1998 17:56:52 -0500
From: Dan Nelson <dnelson@emsphone.com>
To: Brett Glass <brett@lariat.org>, sab@seanet.com
Cc: Doug White <dwhite@resnet.uoregon.edu>, questions@FreeBSD.ORG
Subject: Re: MSDOS extended partitions and "slices"
References: <199808080608.AAA16222@lariat.lariat.org> <199808021131.FAA12204@lariat.lariat.org> <199808080608.AAA16222@lariat.lariat.org> <199809021901.MAA21131@two.sabami.seaslug.org> <199809022113.PAA00535@lariat.lariat.org>
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In the last episode (Sep 02), Brett Glass said:
> At 12:01 PM 9/2/98 -0700, Scott Blachowicz wrote:
> >Brett Glass <brett@lariat.org> wrote:
> >> But.... Waitaminnit. If you have an extended DOS partition with some
> >> number of logical DOS drives within it, you should REALLY see:
> >> 
> >> C: wd1s1
> >> Extended DOS partition: wd1s2
> >>   D: wd1s2a
> >>   E: wd1s2b
> >>   F: wd1s2c
> >> Third partition (FreeBSD, Linux, whatever): wd1s3
> >> Fourth partition: wd1s4
> >
> >Wait a minute...I thought the logical DOS drives within the extended
> >partition corresponded to slices 5 & up....as in...
> >
> >  C: wd1s1
> >  Extended DOS partition: wd1s2
> >    D: wd1s5
> >    E: wd1s6
> >    F: wd1s7
> >  Third partition (FreeBSD, Linux, whatever): wd1s3
> >  Fourth partition: wd1s4
> 
> You see the latter. My point is that this is not logical.

Sure it's logical.  FDISK slices are always numbers; disklabel
partitions are always letters.

wd1s1  .. wd1s4 are the four primary fdisk slices.  Any or all of them
MAY be a container (i.e. extended partition type).  If any of them are,
then they are scanned for valid partition entries (including more
nested extended partitions), and any of those will appear at wd1s5, s6,
etc.  The kernel sets an arbitrary limit of 32 of these slices.

So say you had a mythical 14G IDE drive partitioned with FAT16 DOS
drives:

+--------+-----------------------------------------------------+
|   C:   |                 extended  partition                 |
+--------+- - - - + - - - -+- - - - + - - - - - - - - - - - - -+
         |   D:   |   E:   |   F:   |      extended part.      |
         +--------------------------+ - - - - - - - - - - - - -+
                                    |   G:   |   H:   |   I:   |
                                    +--------------------------+

(boy, I respect Terry more now.  Drawing ascii-art isn't easy :)

In your naming scheme, what would drive 'G:' be?  wd1s2da ?  FreeBSD
would name them like this (after looking at the code in
diskslice_machdep.c; I could be wrong):

wd1s1  C:
wd1s2  extended partition container #1
wd1s3  empty
wd1s4  empty
wd1s5  D:
wd1s6  E:
wd1s7  F:
wd1s8  extended partition container #2
wd1s9  G:
wd1s10 H:
wd1s11 I:

	-Dan Nelson
	dnelson@emsphone.com

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