Managing Serviceguard 11th Edition, Version A.11.16, Second Printing June 2004

Serviceguard at a Glance
What is Serviceguard?
Chapter 124
What is Serviceguard?
Serviceguard allows you to create high availability clusters of HP 9000
or HP Integrity servers. A high availability computer system allows
application services to continue in spite of a hardware or software
failure. Highly available systems protect users from software failures as
well as from failure of a system processing unit (SPU), disk, or local area
network (LAN) component. In the event that one component fails, the
redundant component takes over. Serviceguard and other high
availability subsystems coordinate the transfer between components.
A Serviceguard cluster is a networked grouping of HP 9000 or HP
Integrity servers (host systems known as nodes) having sufficient
redundancy of software and hardware that a single point of failure
will not significantly disrupt service. Application services (individual
HP-UX processes) are grouped together in packages; in the event of a
single service, node, network, or other resource failure, Serviceguard can
automatically transfer control of the package to another node within the
cluster, allowing services to remain available with minimal interruption.
In Figure 1-1, node 1 (one of two SPU's) is running package A, and node
2 is running package B. Each package has a separate group of disks
associated with it, containing data needed by the package's applications,
and a mirror copy of the data. Note that both nodes are physically
connected to both groups of mirrored disks. However, only one node at a
time may access the data for a given group of disks. In the figure, node 1
is shown with exclusive access to the top two disks (solid line), and node
2 is shown as connected without access to the top disks (dotted line).
Similarly, node 2 is shown with exclusive access to the bottom two disks
(solid line), and node 1 is shown as connected without access to the
bottom disks (dotted line).
Mirror copies of data provide redundancy in case of disk failures. In
addition, a total of four data buses are shown for the disks that are
connected to node 1 and node 2. This configuration provides the
maximum redundancy and also gives optimal I/O performance, since
each package is using different buses.
Note that the network hardware is cabled to provide redundant LAN
interfaces on each node. Serviceguard uses TCP/IP network services for
reliable communication among nodes in the cluster, including the
transmission of heartbeat messages, signals from each functioning