For Version 11.50xC6 of IBM Informix,  we added a new Migration Guide chapter on high-availability cluster migration. This information helps you coordinate the migration of all servers in a high-availability cluster or, if necessary, revert all servers in a cluster to the previous version of the server. Chapter topics include information on the additional steps you must perform when preparing to migrate, migrating, and reverting clusters.

If you use high-availability clusters, refer to the information when you upgrade to a new version of Informix, PID, or fix pack, migrate or, if necessary, when you revert to the previous version.

For more information, see High-availability cluster migration.