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

Glossary
disaster
Glossary 431
database. Consistency groups allow you to
configure R1/R2 devices on multiple
Symmetrix frames in MetroCluster/SRDF.
continental cluster A group of clusters
that use routed networks and/or common
carrier networks for data replication and
cluster communication to support package
failover between separate clusters in
different data centers. Continental clusters
are often located in different cities or
different countries and can span 100s or
1000s of kilometers.
Continuous Access A facility provided by
the Continous Access software option
available with the HP StorageWorks E Disk
Array XP series. This facility enables
physical data replication between XP series
disk arrays.
D
data center A physically proximate
collection of nodes and disks, usually all in
one room.
data consistency Whether data are
logically correct and immediately usable; the
validity of the data after the last write.
Inconsistent data, if not recoverable to a
consistent state, is corrupt.
data currency Whether the data contain
the most recent transactions, and/or whether
the replica database has all of the committed
transactions that the primary database
contains; speed of data replication may cause
the replica to lag behind the primary copy,
and compromise data currency.
data loss The inability to take action to
recover data. Data loss can be the result of
transactions being copied that were lost
when a failure occurred, non-committed
transactions that were rolled back as pat of a
recovery process, data in the process of being
replicated that never made it to the replica
because of a failure, transactions that were
committed after the last tape backup when a
failure occurred that required a reload from
the last tape backup. transaction
processing monitors (TPM), message
queuing software, and synchronous data
replication are measures that can protect
against data loss.
data mirroring See See mirroring.
data recoverability The ability to take
action that results in data consistency, for
example database rollback/roll forward
recovery.
data replication The scheme by which
data is copied from one site to another for
disaster tolerance. Data replication can be
either physical (see physical data
replication) or logical (see logical data
replication). In a ContinentalClusters
environment, the process by which data that
is used by the Primary Cluster packages is
transferred to the Recovery Cluster and
made available for use on the Recovery
Cluster in the event of a recovery.
database replication A software-based
logical data replication scheme that is
offered by most database vendors.
disaster An event causing the failure of
multiple components or entire data centers
that render unavailable all services at a
single location; these include natural
disasters such as earthquake, fire, or flood,
acts of terrorism or sabotage, large-scale
power outages.