Managing HP Serviceguard A.11.20.20 for Linux, March 2014

In a cluster with four or more nodes, you may not need a cluster lock since the chance of the cluster
being split into two halves of equal size is very small. However, be sure to configure your cluster
to prevent the failure of exactly half the nodes at one time. For example, make sure there is no
potential single point of failure such as a single LAN between equal numbers of nodes, and that
you don’t have exactly half of the nodes on a single power circuit.
3.2.11 What Happens when You Change the Quorum Configuration Online
You can change the quorum configuration while the cluster is up and running. This includes changes
to the quorum method (for example, from a lock disk to a quorum server), the quorum device (for
example, from one quorum server to another), and the parameters that govern them (for example,
the quorum server polling interval). For more information about the quorum server and lock
parameters, see “Cluster Configuration Parameters ” (page 90).
When you make quorum configuration changes, Serviceguard goes through a two-step process:
1. All nodes switch to a strict majority quorum (turning off any existing quorum devices).
2. All nodes switch to the newly configured quorum method, device and parameters.
IMPORTANT: During Step 1, while the nodes are using a strict majority quorum, node failures
can cause the cluster to go down unexpectedly if the cluster has been using a quorum device before
the configuration change. For example, suppose you change the quorum server polling interval
while a two-node cluster is running. If a node fails during Step 1, the cluster will lose quorum and
go down, because a strict majority of prior cluster members (two out of two in this case) is required.
The duration of Step 1 is typically around a second, so the chance of a node failure occurring
during that time is very small.
In order to keep the time interval as short as possible, make sure you are changing only the quorum
configuration, and nothing else, when you apply the change.
If this slight risk of a node failure leading to cluster failure is unacceptable, halt the cluster before
you make the quorum configuration change.
3.3 How the Package Manager Works
Packages are the means by which Serviceguard starts and halts configured applications. A package
is a collection of services, disk volumes, generic resources , and IP addresses, that are managed
by Serviceguard to ensure they are available.
Each node in the cluster runs an instance of the package manager; the package manager residing
on the cluster coordinator is known as the package coordinator.
The package coordinator does the following:
• Decides when and where to run, halt, or move packages.
The package manager on all nodes does the following:
• Executes the control scripts that run and halt packages and their services.
• Reacts to changes in the status of monitored resources.
3.3.1 Package Types
Three different types of packages can run in the cluster; the most common is the failoverpackage.
There are also special-purpose packages that run on more than one node at a time, and so do not
fail over. They are typically used to manage resources of certain failover packages.
3.3.1.1 Non-failover Packages
There are two types of special-purpose packages that do not fail over and that can run on more
than one node at the same time: the system multi-node package, which runs on all nodes in the
3.3 How the Package Manager Works 43