Disk Quota ( English disk , hard drive and quota , share ',' contingent ') is the limitation of the storage space on storage media , such as hard drives , for an individual user or a group of users. The mechanism is an integral part of most Unix versions or is implemented directly in the system kernel , usually directly in connection with the file system used . Since Windows 2000 , there are disk quotas for operating systems from Microsoft , there are those generally disk quota or shortly contingent called.
In general, the goal is to set a technical limit for memory consumption in order to guarantee that all users can use the available system resources as intended. In environments where storage space is rented out (for example web hosting), in addition to these quality considerations, one also wants to ensure that users only use as much storage space as they pay for.
In general, two storage limits are distinguished, which are set by the system administrator: the so-called soft quota (a "soft" warning limit that must be exceeded for a short time) and the hard disk quota (a "hard" limit that absolutely can not be exceeded can ). Sometimes a grace period is also set, which determines how long the soft limit may be exceeded (see below).
In addition to the distinction between soft limit and hard limit, a distinction is usually made between the usage quota or block quota and the file quota or inode quota . While block quotas limit the actual maximum storage space, file quota limits the number of files and directories (generally inodes ) to a maximum.
While the aforementioned quota types usually refer to a directory and its subdirectories, it is also possible to limit storage space per user; this is possible with Novell Netware . The user's memory credit, the user quota , does not relate to his home directory, but all data are taken into account, of which the user is the owner, regardless of which directory of the tree these data are in.
If a user exceeds his soft quota, he usually receives a message from the system. For example, an email is often sent. The system administrator is often informed of the incident at the same time.
If there is a grace period, the system monitors the memory development of the user in question: If the consumption is not reduced below the soft limit during this time, the system blocks further memory consumption: The soft limit is enforced until the user releases enough memory again .
- Allocation of disk space: quota - page at from the Galileo Computing openbook How do I become a UNIX guru?
- Overview of data storage quotas - page at Microsoft Technet ; As of April 5, 2011