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527Glossary
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 other disk groups, which are used for backup purposes only. It also
contains disk records that define all disk devices on the system.
root disk