Disk quota
Encyclopedia
A disk quota is a limit set by a system administrator
that restricts certain aspects of file system
usage on modern operating system
s. The function of using disk quotas is to allocate limited disk space in a reasonable way.
In addition, administrators usually define a warning level, or soft quota, at which users are informed they are nearing their limit, that is less than the effective limit, or hard quota. There may also be a small grace interval, which allows users to temporarily violate their quotas by certain amounts if necessary.
defines a usage or file quota specific to a certain user or group.
In doing so, an administrator can prevent one user from consuming an entire file system's resources, or create a system of tiered access, whereby users can have different levels of restriction. This is used, for example, by web hosting companies to provide different levels of service based upon the needs and means of individual clients.
In most cases, quotas are also specific to individual file systems. Should an administrator want to limit the usage of a specific user on all file systems, a separate quota would have to be specified on each.
When a soft quota is violated, the system normally sends the user (and sometimes the administrator as well) some sort of message. No further action is typically taken.
Some systems prevent disk write operations that would result in hard quota violations from completing successfully, while others wait until the quota has been physically violated before denying write requests. The user is typically notified through the failed write operation error messages generated by the violating applications, while the administrator is almost always sent a notification as well.
Disk quotas are supported by most modern operating systems, including Unix-like
systems, such as AIX (using JFS or JFS2
filesystem), Linux
(using ext3
, ext4, ext2, xfs (integrated support) among other filesystems), Solaris (using UFS
or ZFS
), Microsoft Windows
starting with Windows 2000
, Novell NetWare
, VMS
, and others. The method of administration for disk quotas varies between each of these operating systems. Unix-like systems typically provide a
where users may violate their quota for a brief period of time. Windows 2000 and newer versions use the "Quota" tab of the disk properties dialog. Other systems provide their own quota management utilities.
System administrator
A system administrator, IT systems administrator, systems administrator, or sysadmin is a person employed to maintain and operate a computer system and/or network...
that restricts certain aspects of file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
usage on modern operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s. The function of using disk quotas is to allocate limited disk space in a reasonable way.
Types of quotas
There are two basic types of disk quotas. The first, known as a usage quota or block quota, limits the amount of disk space that can be used. The second, known as a file quota or inode quota, limits the number of files and directories that can be created.In addition, administrators usually define a warning level, or soft quota, at which users are informed they are nearing their limit, that is less than the effective limit, or hard quota. There may also be a small grace interval, which allows users to temporarily violate their quotas by certain amounts if necessary.
Quotas
Disk quotas are typically implemented on a per-user or per-group basis. That is, a system administratorSystem administrator
A system administrator, IT systems administrator, systems administrator, or sysadmin is a person employed to maintain and operate a computer system and/or network...
defines a usage or file quota specific to a certain user or group.
In doing so, an administrator can prevent one user from consuming an entire file system's resources, or create a system of tiered access, whereby users can have different levels of restriction. This is used, for example, by web hosting companies to provide different levels of service based upon the needs and means of individual clients.
In most cases, quotas are also specific to individual file systems. Should an administrator want to limit the usage of a specific user on all file systems, a separate quota would have to be specified on each.
When a soft quota is violated, the system normally sends the user (and sometimes the administrator as well) some sort of message. No further action is typically taken.
Some systems prevent disk write operations that would result in hard quota violations from completing successfully, while others wait until the quota has been physically violated before denying write requests. The user is typically notified through the failed write operation error messages generated by the violating applications, while the administrator is almost always sent a notification as well.
Disk quotas are supported by most modern operating systems, including Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
systems, such as AIX (using JFS or JFS2
JFS2
Journaled File System or JFS is a 64-bit journaling filesystem created by IBM. Implementation for Linux kernel is available as free software under the terms of the GNU General Public License . There are versions for AIX, eComStation, OS/2 and Linux operating systems...
filesystem), Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
(using ext3
Ext3
The ext3 or third extended filesystem is a journaled file system that is commonly used by the Linux kernel. It is the default file system for many popular Linux distributions, including Debian...
, ext4, ext2, xfs (integrated support) among other filesystems), Solaris (using UFS
Unix File System
The Unix file system is a file system used by many Unix and Unix-like operating systems. It is also called the Berkeley Fast File System, the BSD Fast File System or FFS...
or ZFS
ZFS
In computing, ZFS is a combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include data integrity verification against data corruption modes , support for high storage capacities, integration of the concepts of filesystem and volume management,...
), Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
starting with Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
, Novell NetWare
Novell NetWare
NetWare is a network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, with network protocols based on the archetypal Xerox Network Systems stack....
, VMS
OpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is a computer server operating system that runs on VAX, Alpha and Itanium-based families of computers. Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase...
, and others. The method of administration for disk quotas varies between each of these operating systems. Unix-like systems typically provide a
quota command for both administration and monitoring; graphical front-ends to the command may also be used. Unix and Unix-like operating systems frequently feature a grace periodGrace period
A grace period is a time past the deadline for an obligation during which a late penalty that would have been imposed is waived. Grace periods, which can range from a number of minutes to a number of days or longer, depending on the context, can apply in various situations, including arrival at a...
where users may violate their quota for a brief period of time. Windows 2000 and newer versions use the "Quota" tab of the disk properties dialog. Other systems provide their own quota management utilities.
Common Unix Disk Quota Utilities
- quota - display a user's file system disk quota and usage;
- edquota - Edit user quotas for file system;
- repquota - Summarize quotas for a file system;
- quotacheck - File system quota consistency checker;
- quotaon - Turn file system quotas on and off;
- /etc/fstab (LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
) or /etc/vfstab (Solaris) - list of default parameters for each file system including quota status.