Rolling upgrades (upgrading one Filr or search index server while another continues to serve clients) are not supported when upgrading Filr in a clustered environment.
You must shut down all Filr and search index appliances before you begin the upgrade process. Then restart the appliances after the upgrade is complete.
This issue does not affect small or non-clustered large installations.
For information about how to upgrade Filr, see Upgrading a Large Filr Deployment
in the Filr: Installation, Deployment, and Upgrade Guide.