ZFS - Datasets - Create a Dataset within a Pool

sudo zfs create testpool/some_dataset
 
or
 
sudo zfs create testpool/some_directory

NOTE: A cool feature of the Volumes is that the size of the partition does not need to be specified.

The free space is handled by ZFS.
So there is no need to have to resize partitions when you start running out of space on one.
If you are using more than one disk, this also provides software RAID features like mirror, stripe and parity.

Children Datasets

Datasets can have sub-sets (sub-directories):

pool/parent/child