Glossary of LVM terms

activation:
The process by which a volume group, its disks, or its logical volumes are made available for use

 

allocation policy:
Allocation refers to how data is distributed on a disk. Allocation policy can be contiguous, that is, with no allowable gaps in the set of physical extents on a physical volume, or non-contiguous, with gaps allowed in the set of physical extents

 

bad block relocation:
An LVM feature, employable at the system administrator's option, that provides for the transparent detection of bad disk sectors and the relocation of data from the bad to good disk sectors. The LVM bad block relocation feature can work in conjunction with disk controllers that perform bad sector relocation at the hardware level. Note that the root logical volume does not support software bad block relocation

 

block:
A unit of space for data on a disk, typically having a size of 1024 bytes.

 

device file:
Used to identify and communicate with a device(such as a disk) or pseudo device(such as a logical volume). There are block device files(used for transmitting data in multiple-byte blocks) and character device files(used for transmitting data byte-by-byte). Device files are typically stored in the /dev directory.
By default the full path name of block device files follows a

convention for logical volumes:
/dev/vgnn/lvoln
By default the full path name of character device files follows a convention for logical volumes:/dev/vgnn/rlovoln.

 

extent:
See physical extent, logical extent.

 

file system:
The organization of files on storage devices. The term file system can refer either to the entire file system tree or to a subsection of that file system, contained within a disk section or a logical volume, that can be mounted or unmounted from the tree

 

group file:
The character device file for a volume group

 

logical extent:
A contiguous set of virtual blocks of data contained within a logical volume. A logical extent maps to one(more, if LVM mirroring is used) physical extent. Within a volume group, logical extents are of a fixed size

 

physical extent:
A specific, contiguous set of blocks within a region of a physical volume(disk) where data resides. A physical extent can range, in megabytes, by a power of two from one megabyte to 256 megabytes. Within a volume group, physical extents are of fixed size

 

physical volume:
A disk on which LVM has built data structures, making it an LVM disk. The physical device where data is stored. A physical volume is an entire disk, and has, therefore the device files assigned to section two of the disk. It is not possible to use only part of a disk as an LVM disk. The character device file, /dev/rdsk/cxtxdx, and the block device file, /dev/dsk/cxtxdx,and the appropriate device files for physical volumes.

 

quorum:
The number of physical volumes required to be available in order for a volume group to be activated or manipulated after one or more of a volume group's physical volumes becomes unavailable(because of a disk failure or because it contains stale data after a system crash). A volume group without a quorum of physical volumes remains unavailable

 

raw disk I/O:
The reading and writing of data directly to and from a disk section or a logical volume via the character(raw) device file, independent of file system or swap management

 

swap space:
Space within a disk section, a logical volume, or a file system that is designated to temporarily store the process image

 

volume group:
A set of physical volume(disks) whose space can be combined and logically divided up into logical volumes. Only logical volumes and physical volumes that are a part of a volume group can map together; a physical volume can belong to only one volume group