Managing HP Serviceguard for Linux, Eighth Edition, March 2008

Planning and Documenting an HA Cluster
Power Supply Planning
Chapter 4102
Power Supply Planning
There are two sources of power for your cluster which you will have to
consider in your design: line power and uninterruptible power supplies
(UPS). Loss of a power circuit should not bring down the cluster.
Frequently, servers, mass storage devices, and other hardware have two
or three separate power supplies, so they can survive the loss of power to
one or more power supplies or power circuits. If a device has redundant
power supplies, connect each power supply to a separate power circuit.
This way the failure of a single power circuit will not cause the complete
failure of any critical device in the cluster. For example, if each device in
a cluster has three power supplies, you will need a minimum of three
separate power circuits to eliminate electrical power as a single point of
failure for the cluster.
In the case of hardware with only one power supply, no more than half of
the nodes should be on a single power source. If a power source supplies
exactly half of the nodes, it must not also supply the cluster lock LUN or
quorum server, or the cluster will not be able to re-form after a failure.
See the section on cluster locks in “Cluster Configuration Planning” for
more information.
To provide a high degree of availability in the event of power failure, use
a separate UPS at least for each node’s SPU and for the cluster lock disk
(if any). If you use a quorum server, or quorum server cluster, make sure
each quorum server node has a power source separate from that of every
cluster it serves. If you use software mirroring, make sure power supplies
are not shared among different physical volume groups; this allows you
to set up mirroring between physical disks that are not only on different
I/O buses, but also connected to different power supplies.
To prevent confusion, label each hardware unit and power supply unit
clearly with a different unit number. Indicate on the Power Supply
Worksheet the specific hardware units you are using and the power
supply to which they will be connected. Enter the following label
information on the worksheet: