Logical Volume Manager (LVM) is a subsystem for managing file systems and disk storage space that are structured into logical volumes rather than being restricted to the beginning and end points of a physical disk. Logical volumes can be smaller than the disk or disk array on which they reside, or they can include all or part of several disks or disk arrays. Logical volume boundaries are not required to coincide with the boundaries of physical disks when multiple disks or arrays are used.
Managing logical volumes is done by the Logical Volume Manager, not the
kernel. However, the kernel contains data structures for each volume
group on the system, and the space reserved for LVM data structures must
be sufficient to support the number of volume groups that exist on the
system. This is done by the maxvgs kernel configuration
parameter. A second parameter, no_lvm_disks, is provided
for notifying the kernel at boot time that no logical volumes exist on
the system. This saves the system from having to identify and activate
logical volumes at boot time.
Logical volume groups consist of one or more logical volumes. Logical volume boundaries within a volume group can be configured anywhere on a given disk. However, a single disk device cannot be shared between volume groups. Disk arrays configured as RAID (redundant array of independent disks) arrays for data protection are treated as a single disk device and cannot be shared between volume groups. Individual disks in any array that is not configured as a RAID array are treated as individual devices, and individual devices can be assigned to any volume group as desired by the administrator.