You have a parition d50 comprising slice 0 of a disk:
d50 1 1 c7t60060E80042AEE0000002AEE00000019d0s0
now you want to create soft partitions in it, you can create a 5gb soft partition just by:
# metainit d55 -p d50 5gb
# newfs /dev/md/dsk/d55
You can destroy it by unmounting it, and clearing it
# metaclear d55
You can grow this partition
# metattach d55 1gb
# growfs -M /mount/point /dev/md/rdsk/d55
261/433