Understanding and Designing Serviceguard Disaster Recovery Architectures

physical data
replication
An online data replication method that duplicates I/O writes to another disk on a physical block
basis. Physical replication can be hardware-based where data is replicated between disks over
a dedicated link (for example EMC’s Symmetrix Remote Data Facility or the HP Storage Disk
Array XP Series Continuous Access), or software-based where data is replicated on multiple disks
using dedicated software on the primary node (for example, MirrorDisk/UX).
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 cluster is 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
78 Glossary