With multiple users using a Gluster volume to run their application, there is a possibility of security issues as the users can obtain other user's information. With the subdirectory mount feature, a user can access only their part of the storage, and nothing more. This brings abstraction properly to multiple users consuming the storage. Mounting a part of the Gluster volume (i.e. a subdirectory) provides namespace isolation for users by separating out their directories. Thus, multiple users can use the storage without namespace collisions with other users.
This enhancement has been shipped as a technical preview feature with Red Hat Gluster Storage 3.3.1.