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526 Glossary
Where there are multiple physical access paths to a disk connected to a system, the disk is
called multipathed. Any software residing on the host, (for example, the DMP driver) that
hides this fact from the user is said to provide multipathing functionality.
node
One of the hosts in a cluster.
node abort
A situation where a node leaves a cluster (on an emergency basis) without attempting to
stop ongoing operations.
node join
The process through which a node joins a cluster and gains access to shared disks.
Non-Persistent FastResync
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