Installation guide

42 Chapter 2:Hardware Installation and Operating System Configuration
If power switches are not used in cluster, and a cluster system determines that a hung system is down,
it will set the status of the failed system to DOWN on the quorum partitions, and then restart the hung
system’s services. If the hung system becomes becomes responsive, it will notice that its status is
DOWN, and initiate a system reboot. This will minimize the time that both cluster systems may be able
to issue I/O to the same disk, but it does not provide the data integrity guarantee of power switches. If
the hung system never becomes responsive and no power switches are in use, then a manual reboot is
required.
When used, power switches must be set up according to the vendor instructions. However, some clus-
ter-specific tasks may be required to use a power switch in the cluster. See Section A.1, Setting Up
Power Switches for detailed information on power switches (including information about watchdog
timers). Be sure to take note of any caveats or functional attributes of specific power switch types.
Note that the cluster-specific information provided in this document supersedes the vendor informa-
tion.
When cabling power switches, take special care to ensure that each cable is plugged into the appro-
priate outlet. This is crucial because there is no independent means for the software to verify correct
cabling. Failure to cable correctly can lead to an incorrect system being power cycled, or for one sys-
tem to inappropriately conclude that it has successfully power cycled another cluster member.
After setting up the power switches, perform these tasks to connect them to the cluster systems:
1. Connect the power cable for each cluster system to a power switch.
2. On each cluster system, connect a serial port to the serial port on the power switch that provides
power to the other cluster system. The cable used for the serial connection depends on the type of
power switch. For example, an RPS-10 power switch uses null modem cables, while a network
attached power switch requires a network cable.
3. Connect the power cable for each power switch to a power source. It is recommended to connect
each power switch to a different UPS system. See Section 2.4.3, Configuring UPS Systems for
more information.
After the installation of the cluster software, test the power switches to ensure that each cluster system
can power-cycle the other system before starting the cluster. See Section 3.2.2, Testing the Power
Switches for information.
2.4.3 Configuring UPS Systems
Uninterruptible power supply (UPS) systems provide a highly-available source of power. Ideally, a
redundant solution should be used that incorporates multiple UPS’s (one per server). For maximal
fault-tolerance, it is possible to incorporate two UPS’s per server as well as APC’s Automatic Transfer
Switches to manage the power and shutdown management of the server. Both solutions are solely
dependent on the level of availability desired.