Understanding and Designing Serviceguard Disaster Recovery Architectures

Glossary
A
application restart Starting an application, usually on another node, after a failure. Application can be restarted
manually, which may be necessary if data must be resynchronized before the application can
run (example: Business Recovery Services work like this.) Applications can be restarted by an
operator using a script, which can reduce human error. Or applications can be started on the
local or remote site automatically after detecting the failure of the primary site.
arbitrator Nodes in a disaster recovery architecture that act as tie-breakers in case all of the nodes in a
data center go down at the same time. These nodes are full members of the Serviceguard cluster
and must conform to the minimum requirements. The arbitrator must be located in a third data
center to ensure that the failure of an entire data center does not bring the entire cluster down.
See also quorum server.
asymmetrical
cluster
A cluster that has more nodes at one site than at another. For example, an asymmetrical
metropolitan clusters may have two nodes in one building, and three nodes in another building.
Asymmetrical clusters are not supported in all disaster recovery architectures.
asynchronous data
replication
Local I/O will complete without waiting for the replicated I/O to complete; however, it is expected
that asynchronous data replication will process the I/Os in the original order.
automatic failover Failover directed by automation scripts or software (such as Serviceguard) and requiring no
human intervention. In a Continentalclusters environment, the start-up of package recovery groups
on the Recovery Cluster is without intervention. See also application restart.
B
BC (Business Copy) A PVOL or SVOL in an HP Storage XP series disk array that can be split from or
merged into a normal PVOL or SVOL. It is often used to create a snapshot of the data taken at a
known point in time. Although this copy, when split, is often consistent, it is not usually current.
BCV (Business Continuity Volume) An EMC Symmetrix term that refers to a logical device on the EMC
Symmetrix that may be merged into or split from a regular R1 or R2 logical device. It is often
used to create a snapshot of the data taken at a known point in time. Although this copy, when
split, is often consistent, it is not usually current.
bi-directional
configuration
A Continentalclusters configuration in which each cluster serves the roles of primary and recovery
cluster for different recovery groups. Also known as a mutual recovery configuration.
Business Recovery
Service
Service provided by a vendor to host the backup systems needed to run mission critical applications
following a disaster.
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
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 Serviceguard cluster is a networked grouping of HP 9000 or HP Integrity Servers series 800
servers (host systems known as nodes) or both, having sufficient redundancy of software and
hardware that a single failure cannot significantly disrupt service. 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.
74 Glossary