- SPOF
-
Single Point
of Failure: Component of a system whose failure impairs the
functioning of the whole system.
- Failover
-
Another
similar system component automatically takes over the function of a
failed component.
- Cold Standby
-
The alternative hardware is on
cold standby. The failover must be performed
manually, so the failure will be clearly apparent.
- Warm Standby
-
The backup system runs in the background, so the transfer
can take place automatically. The data on both systems is
automatically synchronized. For the user, the failover is like
a very fast automatic service reboot. However, the current
transaction may be aborted because it was not possible to
synchronize the data prior to failure.
- Hot Standby
-
Both systems permanently run in parallel—data on both
systems is one hundred percent synchronized. Users will not be
aware of any failures. This level cannot usually be reached
without making a corresponding modification to the client. To
run both systems completely synchronously, the connections
to the client must be mirrored one hundred percent. This normally requires
clients that have connections with two or more servers at the
same time and that communicate with all of them. A normal Web
browser cannot do this.
- Load Balancing
-
The distribution of load within a cluster of
computers. Load balancing is used in an LVS
scenario (Linux virtual server), for example
(see Section 12.5.2,
Linux Virtual Server).
- STONITH
-
Shot the other node in the head: Special
hardware and software that ensures that a faulty node does not
write-access distributed media within a cluster, threatening
data consistency in the entire cluster. This involves simply
disconnecting the system from the main power supply.
