Partdisk

At installation time if you see something like the following:

/dev/sdE0: M4-C5064M4SSD2
/dev/sdE0/data
/dev/sdE0/plan9
term%25 inst/start
...
The following Plan 9 disk partitions were found.
/dev/sdE0/plan9
Plan 9 partition to subdivide (/dev/sdE0/plan9)[/dev/sdE0/plan9]:
This is disk/prep; use it to subdivide the PLan 9 partition.
If it is not yet subdivided, a sensible layout will be suggested;
you can probably just type 'w' and then 'q'.
there's a fat partition where the
plan 9 partition table would go.
If you really want to overwrite it, zero
the second sector of the disk adn try again

%25 dd -if /dev/zero -of /dev/sdE0/data -count 50000

That will wipe out the first sectors of the disk and allow Plan 9 to

continue installation.