# zfs create -V 1g space/timf/vol
# zfs list space/timf/vol 
NAME             USED  AVAIL  REFER  MOUNTPOINT
space/timf/vol     1G  3.76G    16K  -
# dd if=/dev/urandom of=/dev/zvol/dsk/space/timf/vol bs=1024k count=100
100+0 records in
100+0 records out
# zfs list space/timf/vol 
NAME             USED  AVAIL  REFER  MOUNTPOINT
space/timf/vol     1G  3.67G   101M  -
# zfs snapshot space/timf/vol@snap
# dd if=/dev/urandom of=/dev/zvol/dsk/space/timf/vol bs=1024k count=60
60+0 records in
60+0 records out
# zfs list -r space/timf/vol
NAME                  USED  AVAIL  REFER  MOUNTPOINT
space/timf/vol       1.10G  3.61G   101M  -
space/timf/vol@snap  60.7M      -   101M  -