Red Hat CLUSTER MANAGER - INSTALLATION AND Administration Manual page 18

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with a power controller type of "None" is useful for simple evaluation purposes, but because it affords
the weakest data integrity provisions, it is not recommended for usage in a production environment.
Ultimately, the right type of power controller deployed in a cluster environment depends on the data
integrity requirements weighed against the cost and availability of external power switches.
Table 2–2, Power Switches summarizes the types of supported power management modules and dis-
cusses their advantages and disadvantages individually.
Table 2–2 Power Switches
Type
Serial-attached
power switches
Network-
attached power
switches
Hardware
Watchdog Timer
Software
Watchdog Timer
No power
controller
Chapter 2:Hardware Installation and Operating System Configuration
Notes
Two serial attached
power controllers are
used in a cluster (one
per member system)
A single network
attached power
controller is required
per cluster
Affords strong data
integrity guarantees
Offers acceptable data
integrity provisions
No power controller
function is in use
Pros
Affords strong data
integrity guarantees. the
power controller itself
is not a single point of
failure as there are two
in a cluster.
Affords strong data
integrity guarantees.
Obviates the need to
purchase external power
controller hardware
Obviates the need to
purchase external power
controller hardware;
works on any system
Obviates the need to
purchase external power
controller hardware;
works on any system
Cons
Requires purchase
of power controller
hardware and cables;
consumes serial ports
Requires purchase
of power controller
hardware. The power
controller itself can be
come a single point
of failure (although
they are typically very
reliable devices).
Not all systems include
supported watchdog
hardware
Under some failure
scenarios, the software
watchdog will not be
operational, opening
a small vulnerability
window
Vulnerable to data
corruption under certain
failure scenarios