# zfs destroy space/vol
# zfs create -V 10m space/vol
# zfs set volsize=20m space/vol
# newfs /dev/zvol/dsk/space/vol
newfs: construct a new file system /dev/zvol/rdsk/space/vol: (y/n)? y
Warning: 2082 sector(s) in last cylinder unallocated
/dev/zvol/rdsk/space/vol:       40926 sectors in 7 cylinders of 48 tracks, 128 sectors
        20.0MB in 1 cyl groups (14 c/g, 42.00MB/g, 20160 i/g)
super-block backups (for fsck -F ufs -o b=#) at:
 32,