Looking for guidelines on when RHCS components can be upgraded in a rolling fashion and when it is best to simply take a full cluster downtime. I am looking at 2-6 node clusters with each node providing a unique set of functions along with common functions. Each node has a dedicated failover node(s). A couple of examples: Minor OS upgrades, e.g. RHEL 5.3 to RHEL 5.5 Major OS upgrades, e.g. RHEL 5.x to RHEL 6.x Errata for key cluster component, e.g. openais, cman, etc, without kernel updates I suspect that minor OS upgrades and errata would survive a rolling upgrade, allowing for the RHCS to run in a mixed mode for a short period of time. The major OS upgrades, since RH can introduce non-passive changes, may require some ingenuity on dividing the cluster up and experiencing a small downtime to flip from one subset to another. I have read the RH documentation on the RHEL 4 to RHEL 5 upgrades which indicate a full cluster downtime is needed to convert GLUM to CMAN configuration. Sorry if this topic has been discussed before, but I could not locate any clear cut rules or direction from the community. Thanks Robert