Quotas – storage for web space and e-mail

The term 'quota' is used in in­for­ma­tion tech­nol­o­gy when referring to the storage limit of a physical or virtual disk, also known as a disk quota. With Unix-based multi-user systems there is a mechanism directly in the system’s core, which dis­trib­utes available memory capacity between different users or user groups. Since Windows 2000, it has also been available for Microsoft operating systems under the term 'disk quotas'.

In web hosting, quotas are of central im­por­tance when it comes to the task of al­lo­cat­ing web space and e-mail storage. Memory limits allow specific per­cent­ages of disk space to be assigned to various users who share a hardware basis. If a user exceeds their allocated storage quota, this is known as a quota violation.

In order to prevent quota vi­o­la­tions, system ad­min­is­tra­tors can define two kinds of storage space limits:

• Soft quotas: this is a 'soft' warning limit. If this limit is exceeded, a user is con­sid­ered 'over quota'. The system sends out a warning message and the ad­min­is­tra­tor is possibly notified. The disk space can still be used until the hard quota limit is reached. Ad­min­is­tra­tors determine a 'grace period', which indicates how long a visitor is allowed to exceed the soft limit.

• Hard quotas: disk space limits, which are defined as hard quotas, cannot be exceeded. Once a user reaches their hard quota, they are prevented from using any more disk space. If this is the case, users should contact their system ad­min­is­tra­tor to obtain a hard quota extension, or they should delete data to free up some space.

Besides the dif­fer­ence in hard and soft limits, quotas can also be defined depending on the storage limit. Possible mea­sur­able quan­ti­ties are data blocks and inodes (from index node).

• Block quotas: this type of storage limits the desk space since each user is allocated a certain number of data blocks.

• Inode quotas: disk quota limits, which refer to the number of inodes, are also known as file quotas since they limit how many files and di­rec­to­ries can be created by a user on the hard disk.

Many users encounter quotas in the web hosting sector when they rent web space or use e-mail hosting with fixed, defined mail storage.

Web space quota

It’s common to host multiple client projects on a shared server using web hosting models like shared hosting. The hardware resources of the physical server are divided among in­di­vid­ual users. Limits such as web space quotas are used in order to state the amount of memory available (which was rented within the chosen hosting package) for each customer project. The web space, which each user is entitled to, cannot therefore be used by anyone else even when storage quotas are dis­trib­uted. Quotas give web hosts the chance to offer web hosting products in different per­for­mance cat­e­gories.

Mail quota

A quota used in the e-mail field limits the space available for storing e-mails and e-mail at­tach­ments and is known as a mail quota. Since many users have e-mail inboxes stored on a shared mail server, mail quotas are there to make sure users don’t exceed their allocated quota. While messages are au­to­mat­i­cal­ly deleted by the mail server when retrieved via POP3 (Post Office Protocol), mails that are accessed via IMAP (Internet Message Access Protocol) are kept on the server until the user decides to delete them them­selves. Con­sid­er­ably larger quotas are needed if IMAP is used instead of POP3.