VERITAS Volume Manager 4.1 Administrator's Guide

Glossary
path
Glossary434
path When a disk is connected to a host, the
path to the disk consists of the HBA (Host
Bus Adapter) on the host, the SCSI or fibre
cable connector and the controller on the
disk or disk array. These components
constitute a path to a disk. A failure on any
of these results in DMP trying to shift all I/O
for that disk onto the remaining (alternate)
paths. Also see active/passive disk arrays,
primary path and secondary path.
pathgroup In case of disks which are not
multipathed by vxdmp, VxVM will see each
path as a disk. In such cases, all paths to the
disk can be grouped. This way only one of the
paths from the group is made visible to
VxVM.
Persistent FastResync A form of
FastResync that can preserve its maps
across reboots of the system by storing its
change map in a DCO volume on disk. Also
see data change object (DCO).
persistent state logging A logging type
that ensures that only active mirrors are
used for recovery purposes and prevents
failed mirrors from being selected for
recovery. This is also known as kernel
logging.
physical disk The underlying storage
device, which may or may not be under
VxVM control.
plex A plex is a logical grouping of subdisks
that creates an area of disk space
independent of physical disk size or other
restrictions. Mirroring is set up by creating
multiple data plexes for a single volume.
Each data plex in a mirrored volume
contains an identical copy of the volume
data. Plexes may also be created to represent
concatenated, striped and RAID-5 volume
layouts, and to store volume logs.
primary path In active/passive disk arrays,
a disk can be bound to one particular
controller on the disk array or owned by a
controller. The disk can then be accessed
using the path through this particular
controller. Also see path and secondary path.
private disk group A disk group in which
the disks are accessed by only one specific
host in a cluster. Also see shared disk group.
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. The disk
header contains a disk ID. All data in the
private region is duplicated for extra
reliability.
public region A region of a physical disk
managed by VxVM that contains available
space and is used for allocating subdisks.
RAID A Redundant Array of Independent
Disks (RAID) is a disk array set up with part
of the combined storage capacity used for
storing duplicate information about the data
stored in that array. This makes it possible
to regenerate the data if a disk failure
occurs.
read-writeback mode A recovery mode in
which each read operation recovers plex
consistency for the region covered by the
read. Plex consistency is recovered by
reading data from blocks of one plex and
writing the data to all other writable plexes.
root configuration The configuration
database for the root disk group. This is
special in that it always contains records for