Infinite hanoi rotation backup (zfs)
http://en.wikipedia.org/wiki/Backup_rotation_scheme#Towers_of_Hanoi
http://lists.debian.org/debian-bsd/2011/12/msg00045.html
use cron or systemd.timer to call hanoizfs.sh periodically
first argument is the duration of a 'day' in seconds, if you want to take daily backups then 86400
second argument is the pool name
third argument is the filesystem name: pool/fs