Veritas Volume Manager 5.0 Migration Guide, HP-UX 11i v3, First Edition, May 2008

80 Glossary
A MirrorDisk/UX mechanism whose use is optional, that tracks outstanding mirror write
requests and provides a basis for the resynchronization of data blocks after a system crash
or power failure.
physical volume
A disk that has been initialized by LVM becomes known as a physical volume.
public region
A region of a physical disk managed by VxVM that contains available space and is used for
allocating subdisks.
private region
A region of a physical disk used to store private, structured VxVM information. The private
region contains a disk header, a table of contents, and a configuration database. The table
of contents maps the contents of the disk.
physical extent
A set of physical disk blocks on a physical volume that forms a basic unit of access in LVM.
This also forms the allocation unit for logical volumes.
snapshot
A temporary extra copy (plex/mirror) created in a volume. A separate volume is created
once its contents are brought in sync with the original volume.
set of continuous physical extents [PEs]
Set of physical sectors (blocks) contained within a single physical volume. A physical
extent is a specific, contiguous region of the disk where data resides. This is of a constant
size usually of 4 MB and has no partitions.
VGRA
The Volume Group Reserved Area (VGRA) is a region on an LVM disk that holds LVM
configuration information and is at a fixed location. The location of this fixed location
depends upon whether the disk is a boot disk or a non-boot disk. For boot disks, the VGRA
starts at sector 2144. For non-boot disks, the VGRA starts at sector 128.
volume group
The collective identity of a set of physical volumes, which provide disk storage for the
logical volumes. A set of physical volumes 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.