What happened to RC1? It was DOA and not released. This release, however, is truly a Release Candidate in that it fixes all the known show-stoppers from 9.1.0-RELEASE and, if nothing serious is found with it, will be re-rolled essentially unchanged as 9.1.1-RELEASE in a couple of days.
Please beat on it as you would an official release and be sure to file any bug reports at https://bugs.freenas.org/projects/freenas
as soon as you can so we'll know if anything needs to be addressed before we GM this one. For a bug tracker query that should show you all the closed tickets for 9.1.1-RC2, please see the README file.
Your Friendly FreeNAS Release Engineer