Designing Disaster Tolerant High Availability Clusters, 10th Edition, March 2003 (B7660-90013)

Glossary
campus cluster
Glossary430
C
campus cluster A single cluster that is
geographically dispersed within the confines
of an area owned or leased by the
organization such that it has the right to run
cables above or below ground between
buildings in the campus. Campus clusters
are usually spread out in different rooms in
a single building, or in different adjacent or
nearby buildings. See also extended distance
cluster.
cascading failover Cascading failover is
the ability of an application to fail from a
primary to a secondary location, and then to
fail to a recovery location on a different site.
The primary location contains a
metropolitan cluster built with MetroCluster
EMC SRDF, and the recovery location has a
standard MC/ServiceGuard cluster.
client reconnect Users access to the
backup site after failover. Client reconnect
can be transparent, where the user is
automatically connected to the application
running on the remote site, or manual,
where the user selects a site to connect to.
cluster An MC/ServiceGuard cluster is a
networked grouping of HP 9000 series 800
servers (host systems known as nodes)
having sufficient redundancy of software
and hardware that a single failure will not
significantly disrupt service.
MC/ServiceGuard software monitors the
health of nodes, networks, application
services, EMS resources, and makes failover
decisions based on where the application is
able to run successfully.
cluster alarm Time at which a message is
sent indicating that the Primary Cluster is
probably in need of recovery. The
cmrecovercl command is enabled at this
time.
cluster alert Time at which a message is
sent indicating a problem with the cluster.
cluster event A cluster condition that
occurs when the cluster goes down or enters
an UNKNOWN state, or when the monitor
software returns an error. This event may
cause an alert messages to be sent out, or it
may cause an alarm condition to be set,
which allows the administrator on the
Recovery Cluster to issue the cmrecovercl
command. The return of the cluster to the UP
state results in a cancellation of the event,
which may be accompanied by a cancel event
notice. In addition, the cancellation disables
the use of the cmrecovercl command.
cluster quorum A dynamically calculated
majority used to determine whether any
grouping of nodes is sufficient to start or run
the cluster. Cluster quorums prevent
split-brain syndrome which can lead to data
corruption or inconsistency. Currently at
least 50% of the nodes plus a tie-breaker are
required for a quorum. If no tie-breaker is
configured, then greater than 50% of the
nodes is required to start and run a cluster.
command device A disk area in the HP
StorageWorks XP series disk array used for
internal system communication. You create
two command devices on each array, each
with alternate links (PV links).
consistency group A set of Symmetrix
RDF devices that are configured to act in
unison to maintain the integrity of a