File store high availability

A messaging engine in a cluster bus member can failover between servers in the cluster. When this failover occurs, the messaging engine must be able to access the saved state in its file store from any of the servers in the cluster.

File stores can be used in highly available environments. To make a file store highly available, use hardware or software facilities that can maximize the availability of the file store data, for example, a storage area network (SAN).

Tips:

For a messaging engine in an application server that might run on several nodes, place the log file and store files in a directory in a shared file system. For a messaging engine that runs in an application server and always runs on the same node, place the log file and store files in any accessible directory. This directory can be in a local file system to that node.
Do not configure the file store so that the messaging engine, depending on its location, uses different copies of the log file and store files.

You can test whether a shared file system can support the failover of messaging engines by running the File System Locking Protocol Test for WebSphere® Application Server. To run the test see, IBM File System Locking Protocol Test for WebSphere Application Server.

WebSphere Application Server supports two styles of file system access to enable high availability:

Cluster-managed file system: This style of file system access uses high availability clustering and failover of shared disks to ensure that the directories for the file store are accessible from the server that is currently running the messaging engine. The directories are located on file systems in the shared disks, and high availability cluster scripts are used to mount the file systems on the node that contains the server that is running the messaging engine.

Networked file system: This style of file system access allows remote files to be accessed over a network. The most popular protocols for accessing remote files are Common Internet File System (CIFS) and Network File System (NFS). Version 4 of NFS supports automated failover to ensure access locking. Access locking ensures the integrity of the log files; that is, only a single client process can access the log at a time.

Note: It is important to check that the file system configuration is correct, because it cannot be checked by the WebSphere Application Server configuration system or messaging engine. Errors only surface at run time, so thorough failover testing is important.