Managing Serviceguard Nineteenth Edition, Reprinted June 2011

Cluster Configuration Planning
A cluster should be designed to provide the quickest possible recovery from failures. The actual
time required to recover from a failure depends on several factors:
• The value of the cluster MEMBER_TIMEOUT.
See MEMBER_TIMEOUT under “Cluster Configuration Parameters ” (page 105) for
recommendations.
• The availability of raw disk access. Applications that use raw disk access should be designed
with crash recovery services.
• The application and database recovery time. They should be designed for the shortest recovery
time.
In addition, you must provide consistency across the cluster so that:
• User names are the same on all nodes.
• UIDs are the same on all nodes.
• GIDs are the same on all nodes.
• Applications in the system area are the same on all nodes.
• System time is consistent across the cluster.
• Files that could be used by more than one node, such as files in the /usr directory, must be
the same on all nodes.
About Cluster-wide Device Special Files (cDSFs)
Under agile addressing on HP-UX 11i v3, each device has a unique identifier as seen from a given
host; this identifier is reflected in the name of the Device Special File (DSF). See “About Device
File Names (Device Special Files)” (page 77) for more information.
Because DSF names may be duplicated between one host and other, it is possible for different
storage devices to have the same name on different nodes in a cluster, and for the same piece of
storage to be addressed by different names. Cluster-wide device files (cDSFs), available as of the
September 2010 HP-UX Fusion Release, ensure that each storage device used by the cluster has
a unique device file name.
IMPORTANT: Check the latest version of the release notes (at the address given in the preface
to this manual) for information about Serviceguard support for cDSFs.
HP recommends that you use cDSFs for the storage devices in the cluster because this makes it
simpler to deploy and maintain a cluster, and removes a potential source of configuration errors.
See “Creating Cluster-wide Device Special Files (cDSFs)” (page 150) for instructions.
Points To Note
• cDSFs can be created for any group of nodes that you specify, provided that Serviceguard
A.11.20 is installed on each node.
Normally, the group should comprise the entire cluster.
• cDSFs apply only to shared storage; they will not be generated for local storage, such as root,
boot, and swap devices.
• Once you have created cDSFs for the cluster, HP-UX automatically creates new cDSFs when
you add shared storage.
• HP recommends that you do not mix cDSFs with persistent (or legacy) DSFs in a volume group.
You cannot use cmpreparestg (1m) on a volume group in which they are mixed.
See “About Easy Deployment” (page 100) for more information about cmpreparestg.
Cluster Configuration Planning 99