After some unsuccessful experiments with zfs snapshots I see following output for 'zfs list':
$ zfs list
NAME USED AVAIL REFER MOUNTPOINT
tank 1.48T 2.64T 25.4K none
tank/home 92.6K 2.64T 92.6K legacy
tank/jails 1.46T 2.64T 41.1K legacy
tank/jails/jail05 18.3G 2.64T 17.7G /jails/jail05
tank/jails/jail06 18.3G 2.64T 17.7G /jails/jail06
tank/jails/somefldr 18.3G 2.64T 17.7G /jails/jail06
Now there are two mountpoints with the same name (/jails/jail06) pointing to different zfs directories. The zfs unmount command doesn't work.
$ sudo zfs unmount /jails/jail06
cannot unmount '/jails/jail06': not a mountpoint
Looking for any advice to solve this issue. Thanks in advance!
Upd:
zfs mount
displays no /jails/jail06 mounted.
You can use mount to see whether the filesystem is actually mounted. Just because it has a given mountpoint doesn't mean it's mounted.
It looks like you have set the mountpoint for the zfs filesystems and they are not mounted.