A high availability cluster is
a grouping of HP 9000 series 800 servers having sufficient redundancy
of software and hardware components that a single point of failure
will not disrupt the availability of computer services. High availability
clusters configured with Oracle Parallel Server are known as
OPS clusters. Figure 1-1 “Overview of Oracle Parallel Server
Configuration on HP-UX ” shows a very simple picture of the basic configuration
of an OPS cluster on HP-UX.
In the figure, two loosely coupled HP 9000 series 800 systems
(each one known as a node) are running separate
instances of Oracle software that read data from and write data
to a shared set of disks. Clients connect to one node or the other
via LAN.
OPS on HP-UX lets you maintain a single database image that
is accessed by the HP 9000 servers in parallel, thereby gaining
added processing power without the need to administer separate databases. ServiceGuard
OPS Edition handles issues of concurrent access to the same resources
by different servers and ensures data integrity. Further, when properly
configured, ServiceGuard OPS Edition provides a highly available
database that continues to operate even if one hardware component
should fail.
Group Membership |
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OPS 8.1.x and later systems implement the concept of group membership,
which allows multiple instances of OPS to run on each node. Related
processes are configured into groups. Groups
allow processes in different instances to choose which other processes
to interact with. This allows the support of multiple databases
within one SG/OPS cluster.
A Group Membership Service (GMS) component provides a process monitoring
facility to monitor group membership status. GMS is provided by
the cmgmsd daemon, which is an HP component installed with ServiceGuard
OPS Edition.
Figure 1-2 “Group Membership Services” shows how group membership works.
Nodes 1 through 4 of the cluster share the Sales database, but only
Nodes 3 and 4 share the HR database. Consequently, there is one
instance of OPS each on Node 1 and Node 2, and there are two instances
of OPS each on Node 3 and Node 4. The OPS processes accessing the
Sales database constitute one group, and the OPS processes accessing
the HR database constitute another group.
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