VERITAS Volume Manager 4.1 Migration Guide

Glossary 83
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.