VERITAS Volume Manager 3.5 Migration Guide (September 2004)

Glossary
61
Glossary
block A unit of space for data on a disk, typically having a size of 1024-bytes.
Dirty Region Logging Dirty Region Logging (DRL) is an optional property of a volume, used to provide a
speedy recovery of mirrored volumes after a system failure. DRL keeps track of the regions that have changed
due to I/O writes to a mirrored volume.
file system The organization of files on storage devices. The term file system can refer either to the entire file
system or to a subsection of that file system, contained within a disk section or a logical volume that can be
mounted or unmounted from that tree.
logical volume A logical structure that is a map of storage areas on physical volumes. A logical volume can
be conceptualized as a storage device of flexible size. The data in a logical volume can be mapped to one or
more physical volumes. A virtual disk device that represents a contiguous virtual disk space that maps to
single or multiple areas on a single or multiple physical volumes.
LVM The Logical Volume Manager (LVM) is a subsystem for managing disk space. LVM is an HP-UX
product, similar to VxVM.
LIF The Logical Interchange Format (LIF) is a HP mass-storage format that can be used for interchange of
files among various HP computer systems. Each boot disk has a LIF directory that contains boot programs.
logical Extent A set of logical blocks that maps to one physical extent and is a basic unit of access in a
logical volume.
LVMREC The LVM record, which is an identifier that is set on each disk when it is initialized the first time
by LVM. There are two copies of the LVMREC; one is at sector 8, while the other is at sector 72.
mirror disk/UX HP-UX software product that allows disk mirroring as part of LVM functionality. Mirror
Disk/UX allows up 2 mirror copies in a volume.
Mirror Write Cache (MWC) 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.