Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

512 Glossary
A form of FastResync that cannot preserve its maps across reboots of the system because it stores its
change map in memory.
object
An entity that is defined to and recognized internally by VxVM. The VxVM objects are: volume,
plex, subdisk, disk, and disk group. There are actually two types of disk objects—one for the physical
aspect of the disk and the other for the logical aspect.
parity
A calculated value that can be used to reconstruct data after a failure. While data is being written to a
RAID-5 volume, parity is also calculated by performing an exclusive OR (XOR) procedure on data.
The resulting parity is then written to the volume. If a portion of a RAID-5 volume fails, the data that
was on that portion of the failed volume can be recreated from the remaining data and the parity.
parity stripe unit
A RAID-5 volume storage region that contains parity information. The data contained in the parity
stripe unit can be used to help reconstruct regions of a RAID-5 volume that are missing because of I/
O or disk failures.
partition
The standard division of a physical disk device, as supported directly by the operating system and
disk drives.
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 the 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