Understanding and Designing Serviceguard Disaster Recovery Architectures

planned downtime An anticipated period of time when nodes are taken down for hardware maintenance, software
maintenance (OS and application), backup, reorganization, upgrades, and so on (software or
hardware).
PowerPath A host-based software product from Symmetrix that delivers intelligent I/O path management.
PowerPath is required for M by N Symmetrix configurations using Metrocluster with EMC SRDF.
Primary Cluster A cluster in production that has packages protected by the HP ContinentalClusters product.
primary package The package that normally runs on the Primary Cluster in a production environment.
pushbutton failover Use of the cmrecovercl command to allow all package recovery groups to start up on the
Recovery Cluster following a significant cluster event on the Primary Cluster.
PV links A method of LVM configuration that allows you to provide redundant disk interfaces and buses
to disk arrays, thereby protecting against single points of failure in disk cards and cables.
PVOL A primary volume configured in an XP series disk array that uses Continuous Access. PVOLs are
the primary copies in physical data replication with Continuos Access on the XP.
Q
quorum server A cluster node that acts as a tie-breaker in a disaster recovery architecture in case all of the nodes
in a data center go down at the same time. See also arbitrator.
R
R1 The Symmetrix term indicating the data copy that is the primary copy.
R2 The Symmetrix term indicating the remote data copy that is the secondary copy. It is normally
read-only by the nodes at the remote site.
Recovery Cluster A cluster on which recovery of a package takes place following a failure on the Primary Cluster.
recovery group
failover
A failover of a package recovery group from one cluster to another.
recovery package The package that takes over on the Recovery Cluster in the event of a failure on the Primary
Cluster.
regional disaster A disaster, such as an earthquake or hurricane, that affects a large region. Local, campus, and
proximate metropolitan clusters are less likely to protect from regional disasters.
remote failover Failover to a node at another data center or remote location.
resynchronization The process of making the data between two sites consistent and current once systems are restored
following a failure. Also called data resynchronization.
rolling disaster A second disaster that occurs before recovering from a previous disaster, for example, while data
is being synchronized between two data centers after a disaster, one of the data centers fails,
interrupting the data synchronization process. Rolling disasters may result in data corruption that
requires a reload from tape backups.
S
single point of
failure (SPOF)
A component of a cluster or node that, if it fails, affects access to applications or services. See
also multiple points of failure.
single system high
availability
Hardware design that results in a single system that has availability higher than normal. Hardware
design examples are:
• n+1 fans
• n+1 power supplies
• multiple power cords
• online addition or replacement of I/O cards, memory
special device file The device file name that the HP-UX operating system gives to a single connection to a node, in
the format /dev/devtype/filename.
split-brain
syndrome
When a cluster reforms with equal numbers of nodes at each site, and each half of the cluster
thinks it is the authority and starts up the same set of applications, and tries to modify the same
80 Glossary