In message <[EMAIL PROTECTED]>, [EMAIL PROTECTED] writes:
>Mike, I'll pay back your effort in replying to this long thing by
>working up a patch for the "disklabel" manpage (at least) and, if you
>want, I'll CC you so you can veto things you don't like. I do worry
At the risk of adding to the confusion, here is a less wordy
description of the various disk layouts. The term `dangerously
dedicated' seems to be used to refer to either options (B) or (C),
so I will avoid using that term:
(A) Normal sliced disk (assuming sectors/track = 63)
sector 0: boot0 and the DOS slice table
sectors 1..62: unused
<start of slice 1>
<start of 'a' partition>
sector 63: boot1
sector 64: disklabel
sectors 65-78: boot2
sectors 79-92: 'a' partition filesystem superblock
Note that the disklabel, which contains a list of the partitions
within a slice is actually contained within the space allocated to
the first partition. To ensure that this does not get clobbered by
the filesystem, the first 8k of every ffs filesystem is reserved for
boot code and the disklabel.
(B) Dedicated format created by sysinstall
<start of slice 1>
<start of 'a' partition>
sector 0: boot1 and the DOS slice table, where
the slice table contains one slice
(slice 1) covering the entire disk,
including sector 0.
sector 1: disklabel
sector 2-15: boot2
sectors 16-31: 'a' partition filesystem superblock
In this case, there is no boot0, and boot1 serves as the boot
loader that is invoked by the BIOS. Here, all of the boot code
is contained within the first slice and also within the first
partition. Again, the 8k reserved at the start of every ffs
filesystem protects the boot code. Sysinstall sets up fstab to
refer to the partitions as e.g. /dev/ad0s1a (I think).
(C) Dedicated format using dummy slice
<start of slice 4>
<start of 'a' partition>
sector 0: boot1 and the DOS slice table. The slice
table contains a single entry (slice 4)
that starts at sector 0 and has a size
of 50000 sectors, whatever the real disk
size is.
sector 1: disklabel
sector 2-15: boot2
sectors 16-31: 'a' partition filesystem superblock
This is like (B) except that slice 4 instead of slice 1 is used, and
the size of the slice in the slice table is bogus. The partitions
on such a disk are usually accessed using the compatibility slice
names such as /dev/ad0a.
Ian
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