The following instructions describe your tuning options for Session Clustering. A complete list of the Session Clustering directives is located in the Reference section. Additional information can also be found in Appendix A - Troubleshooting Zend Platform.
In most cases, Session Clustering should be set to memory: mod_cluster.storage.use_permanent_storage=0 (in HA mode, storing sessions permanently is overkill, so if you do so, at least cache the sessions in memory and flush infrequently).
In case HD is used, you might like to tune the mod_cluster.storage.memory_cache_size and mod_cluster.storage.flush_delta directives, to get a better performance by using Memory-to-HD wisely. Flush_Delta=0 means direct write to disk, otherwise number of seconds until flushed from memory to HD.
If you don't need the Sessions Statistics, you can set a lower rate of updates to the log, with the directive: mod_cluster.statistics_delta_minutes.
Session Lifetime and Garbage Collection: mod_cluster.session_lifetime = 900 (15 min)
mod_cluster.garbage_collection_delta = 1800 (30 min)
To fine tune the broadcast, you should concentrate this directive: mod_cluster.ha.broadcast_delta. What needs to be considered is the possibility of all SC daemons broadcasting at the same time.
Have the mod_cluster.storage.dir_levels directive set to min 2 and max 2.
Log rotation - you can set the number of minutes between checks and minimum log size to rotate in the following directives:
mod_cluster.storage.filename_cache_num_entries - (1-1024)