There is an opened issue concerning this topic: https://github.com/owncloud/core/issues/1344. It might be ready for owncloud 9.2.
For now, as PVince81 has suggested in the issue I’ve posted above, you can run an SQL query to see the current disc usage by user:
MariaDB [owncloud]> select m.user_id, fc.size from oc_mounts m, oc_filecache fc, oc_storages s where m.mount_point=concat('/', m.user_id, '/') and s.numeric_id=m.storage_id and fc.storage=m.storage_id and fc.name='files'; +---------+---------+ | user_id | size | +---------+---------+ | admin | 163 | | user1 | 4774179 | | user2 | 1571107 | +---------+---------+ 3 rows in set (0.00 sec)
