"When you are running your own web hosting, it is important to monitor how much space is being used by each user. This is not a simple task to be done manually since one of the users or group could fill up the whole hard disk, preventing others from availing any space. Therefore, it is important to allow each user or group their own hard disk space called quota and locking them out from using more than what is allotted.
The system administrator sets a limit or a disk quota to restrict certain aspects of the file system usage on a Linux operating system.
for more info read : http://www.firewall.cx/linux-knowledgebase-tutorials/linux-administration/838-linux-file-system-quotas.html
