Designing Disaster Recovery Clusters using Metroclusters and Continentalclusters, Reprinted October 2011 (5900-1881)

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.
rehearsal package The recovery cluster package used to validate the recovery environment and procedure as part
of a rehearsal operation.
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
• on-line addition or replacement of I/O cards, memory, etc.
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
data, resulting in data corruption. Serviceguard architecture prevents split-brain syndrome in all
cases unless dual cluster locks are used.
SRDF (Symmetrix Remote Data Facility) A level 1-3 protocol used for physical data replication between
EMC Symmetrix disk arrays.
sub-clusters Sub-clusters are clusterwares that run above the Serviceguard cluster and comprise only the nodes
in a Metrocluster site. Sub-clusters have access only to the storage arrays within a site.
SVOL A secondary volume configured in an P9000 or XP series disk array that uses Continuous Access.
SVOLs are the secondary copies in physical data replication with Continuos Access on the P9000
or XP.
SymCLI The Symmetrix command line interface used to configure and manage EMC Symmetrix disk
arrays.
Symmetrix device
number
The unique device number that identifies an EMC logical volume.
synchronous data
replication
Each data replication I/O waits for the preceding I/O to complete before beginning another
replication. Minimizes the chance of inconsistent or corrupt data in the event of a rolling disaster.
T
transaction
processing monitor
(TPM)
Software that allows you to modify an application to store in-flight transactions in an external
location until that transaction has been committed to all possible copies of the database or
filesystem, thus ensuring completion of all copied transactions. A TPM protects against data loss
at the expense of the CPU overhead involved in applying the transaction in each database replica.
Software that provides a reliable mechanism to ensure that all transactions are successfully
committed. A TPM may also provide load balancing among nodes.
transparent
failover
A client application that automatically reconnects to a new server without the user taking any
action.
520 Glossary