So I noticed that if I run disk/prep -b -a^(arenas isect bloom)
against my disk it goes ahead and creates a partition table that
has arenas starting at sector 0.

If I manually create partitions, /sys/src/cmd/disk/prep/prep.c:24
guards against using sectors 0 and 1 unless it's a 9fat partition.

Why is there a difference in the way an automated partition
set is created vs a manual one?

Jim