AG (file systems)
Encyclopedia
An AG or allocation group is a subvolume in a file system
which maintains its own track of free blocks and file data (and its own journal, in the case of XFS
).
This makes simultaneous file operations possible; only one write can happen to an AG at any time, but multiple operations can be performed on the file system, each happening in a different AG. In SMP
systems multiple CPU
s can write to different AGs, enabling physically concurrent disk operations on a single file system. (Hard disk
s can only do one thing at a time. However, file systems can span hard disks in various ways (RAID
stripe, volume management, etc.)).
Used by these file systems:
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...
which maintains its own track of free blocks and file data (and its own journal, in the case of XFS
XFS
XFS is a high-performance journaling file system created by Silicon Graphics, Inc. It is the default file system in IRIX releases 5.3 and onwards and later ported to the Linux kernel. XFS is particularly proficient at parallel IO due to its allocation group based design...
).
This makes simultaneous file operations possible; only one write can happen to an AG at any time, but multiple operations can be performed on the file system, each happening in a different AG. In SMP
Symmetric multiprocessing
In computing, symmetric multiprocessing involves a multiprocessor computer hardware architecture where two or more identical processors are connected to a single shared main memory and are controlled by a single OS instance. Most common multiprocessor systems today use an SMP architecture...
systems multiple CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
s can write to different AGs, enabling physically concurrent disk operations on a single file system. (Hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
s can only do one thing at a time. However, file systems can span hard disks in various ways (RAID
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
stripe, volume management, etc.)).
Used by these file systems:
- XFSXFSXFS is a high-performance journaling file system created by Silicon Graphics, Inc. It is the default file system in IRIX releases 5.3 and onwards and later ported to the Linux kernel. XFS is particularly proficient at parallel IO due to its allocation group based design...
from SGISilicon GraphicsSilicon Graphics, Inc. was a manufacturer of high-performance computing solutions, including computer hardware and software, founded in 1981 by Jim Clark...
, an XFS AG can have a max size of 4GB