You can create quotas with a qtree as their target; these quotas are called tree quotas. You can also create user and group quotas for a specific qtree. In addition, quotas for a volume are sometimes inherited by the qtrees contained by that volume.
How tree quotas work
You can create a quota with a qtree as its target to limit how large the target qtree can become. These quotas are also called tree quotas.
How user and group quotas work with qtrees
Tree quotas limit the overall size of the qtree. To prevent individual users or groups from consuming the entire qtree, you specify a user or group quota for that qtree.