On Sun, 17 Feb 2013, Erich Dollansky wrote:
gpart destroy -F da0
diskinfo da0
dd if=/dev/zero of=/dev/da0 bs=512 count=34
dd if=/dev/zero of=/dev/da0 bs=512 count=34 seek=312581774
Someone here on the lists (I unfortunately forget who) showed a
sneaky easier way to do this:
gpart destroy -F da0
gpart create -s gpt da0
gpart destroy -F da0
This did not make a difference.
It's an easier way to destroy the backup table at the end of the disk,
whether one was there before or not, without having to calculate the
location.
gpart show -p da0
gpart create -s MBR da0
gpart add -t freebsd da0
gpart show -p da0
gpart show -p da0s1
gpart set -a active -i 1 da0
#
# The following line always gives an error:
#
# gpart create -s BSD da0s1
'destroy' is not recursive. It destroys the geom found on the device
given, but does not write to any geoms inside those geoms.
This is obvious. What surprises me is that create does not write a new
and empty description to the disk.
It does, but not being recursive, it does not destroy the geoms inside
the one given to the command (da0). You had:
da0 (MBR)
da0s1 (bsdlabel)
After the destroy, it became
da0 (null)
da0s1 (bsdlabel)
This can happen with any of the setups where there are geoms inside
other geoms.
The second part of your question, about da0 starting a block zero:
[X220]...Appl/Some Tools (root) > gpart show da0
=> 63 312581745 da0 MBR (149G)
63 312581745 1 freebsd [active] (149G)
[X220]...Appl/Some Tools (root) > gpart show da0s1
=> 0 312581745 da0s1 BSD (149G)
0 312581745 - free - (149G)
That shows slice one starts at block 63, standard for MBR. The space
inside the slice (da0s1) starts at block 0 *of the slice*.
This is a bit confusing for me but it does not really matter as long as
the programs get it straight.
This is again because of the geom inside a geom setup. The actual start
block is the start of the slice (block 63) plus the start of the FreeBSD
partition inside the slice (currently 0). When you create FreeBSD
partitions inside da0s1, they will have nonzero offsets from the start
of the slice. There are examples shown here:
http://forums.freebsd.org/showpost.php?p=206204&postcount=11
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