The Oracle ZFS Storage Appliance manages physical storage using a pooled storage model where all filesystems and LUNs share common space. Filesystems never have an explicit size assigned to them, and only take up as much space as they need. LUNs reserve enough physical space to write the entire contents of the device, unless they are thinly provisioned, in which case they behave like filesystems and use only the amount of space physically consumed by data.
This system provides maximum flexibility and simplicity of management in an environment when users are generally trusted to do the right thing. A stricter environment, where user's data usage is monitored and/or restricted, requires more careful management.
These topics define terminology and how to manage space usage, on a per-share or per-user basis, using quotas and reservations.