External Data Storage

The application must be capable of storing all required data and configuration information on shared disks. The exception to this rule is a true shared nothing cluster, described in section Shared Nothing Cluster.

To meet this requirement, you may need specific setup options or soft links. For example, a product may only install in /usr/local. This would require linking /usr/local to a file system mounted from the shared storage device or mounting file system from the shared device on /usr/local.

The application must also store data to disk rather than maintaining it in memory. The takeover system must be capable of accessing all required information. This precludes the use of anything inside a single system inaccessible by the peer, such as NVRAM accelerator boards and other disk-caching mechanisms contained in a local host.

Licensing and Host Name Issues

The application must be capable of running on all servers designated as potential hosts, which means strict adherence to licensing requirements and host name dependencies. Changing host names can lead to significant management issues when multiple systems have the same host name after an outage. Custom scripting to modify a system host name on failover is not recommended. It is better to configure applications and licensing to run properly on all hosts.