CheckQuota is the professional monitor program for directories. It monitors directory size and sends alerts if a limit was exceeded.
But CheckQuota has much more features. So it can works like a real disk quota program. Real disk quota this means the following:
For every folder it is possible to specify one or more users. If a specified user exceeds the directory usage limit, all write processes will be prevented for them. The user can read and delete his data, but writing is not possible. So a system administrator can control and stop increase of directory size. When user deletes data, in order that the directory usage falls under specified limit, he gets all the write access back. CheckQuota is must-have for every system administrator and should be installed on every server.