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

Glossary
single point of failure (SPOF)
Glossary436
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.
MC/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.
SVOL A secondary volume configured in an
XP series disk array that uses Continuous
Access. SVOLs are the secondary copies in
physical data replication with Continous
Access on the 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.