Logical
volumes and logical management make it easier to manage disk space. If a LVM
hosted file system needs more space, it can be allocated to its logical volume
from the free space in its volume group and the file system can be resized. If
a disk starts to fail, a replacement disk can be registered as a physical
volume group and the logical volume's extents can be migrated to the new disk.
Physical devices are the storage devices used
to persist data stored in a logical volume. These are block devices and could
be disk partitions, whole disks, RAID arrays or SAN disks. A device must
be initialized as an LVM physical volume in order to be used with LVM. The
entire device will be used as a physical volume.
Physical Volumes (PV) are used to register underlying physical devices for use
in volume groups. LVM automatically segments PVs into physical extents (PE),
these are small chunks of data that act as the smallest storage block on a PV.
Volume groups (VG) are storage pools made up of one or more physical
volume. A PV can only be allocated to a single VG. A VG can consist of unused
space and any number of logical volumes.
Logical Volumes (LV) are created from free physical extents in a volume group and provide the
“storage” device used by applications, users, and the operating system. LVs are
collection logical extents (LE) which map to physical extents, the smallest
storage chunk of a PV. By default, each LE will map to one PE.
