OMS Sever HA Shared Filesystem Architecture

There are two possible ways to set up a High Availability (HA) OMS environment: the Shared Filesystem Architecture, and the Data Replication Architecture (introduced in UAC 7.9).

This page explains the Shared Filesystem Architecture. The Architecture Details section explains how the Shared Filesystem setup works. The Configuration Steps section explains how to configure this architecture.

Architecture Details

Shared OMS Message Database

The OMS message database must reside on a shared file system accessible by each of the OMS Server cluster members. The shared OMS message database is utilized for the following capabilities:

1. The active OMS server selection process.
2. OMS message availability in fail-over scenarios.

The OMS Server cluster members determine the active OMS Server by obtaining an exclusive lock on a lock file in the OMS message database directory. The active OMS Server holds the file lock for the entire time it is executing. The inactive OMS Servers check every three seconds to see if the file lock is available. If the active OMS Server terminates, the exclusive file lock will be released, allowing one of the inactive OMS Servers to obtain exclusive access to the file lock. The OMS Server that obtains the file lock becomes the active OMS Server in the cluster.

The file system on which the OMS message database resides may be on a SAN or a network file system. The file system must support distributed file locks. On POSIX-based systems, such as UNIX and Linux, NFS version 4 or higher may be used. NFS version 3 does not support reliable file locks and must not be used. On Windows-based systems, SMB accessible file systems do provide support for file locks. Other network file systems are available. Check with the file system vendor to determine if POSIX compliant distributed file locks are supported.

The shared file system on which the OMS message database is located should be deployed as an HA configuration. If the shared file system becomes unavailable, the OMS HA cluster members will not have access to the OMS message database and will be rendered inoperable.

OMS Server Cluster

An OMS Server cluster consists of two or more OMS Servers sharing a common OMS message database. The OMS Servers should be installed on different machines in order to provide fault tolerance in the case of machine failure. The OMS message database contains platform-specific data types. Consequentially, all OMS Servers in the HA cluster must be installed on the same operating systems and hardware architectures - data size (32-bit or 64-bit) and encoding (little-endian or big-endian) - must be the same between all OMS Server cluster members.

Each OMS Server in the HA cluster must be configured to use the same, shared OMS message database. The OMS Server SPOOL_DIRECTORY OMS configuration option specifies the location of the OMS message database. Its value must be the same for all cluster members.

Configuration Steps

Configuring a High Availability (HA) cluster with a Shared Filesystem architecture consists of the following steps:

Step 1	Deploy the OMS message database on a shared file system that is available to all OMS Server cluster members.
Step 2	Configure the OMS Server cluster members to use the shared OMS message database.
Step 3	Configure the OMS clients with the list of OMS server cluster members.