You could upgrade directly to 9.1(5) but then you will need to enter your configuration manually. The upgrade path is in place to automatically convert any configuration that requires it. from 8.4 to 9.1 there aren't many major changes as there was from 8.2 to 8.3. So, unless you have some really non standard configuration, you should be fine.
I would also suggest going through the 9.1 release notes just to make sure that there are no features, caveats, or system requirements that might cause you some issues.
BenefitsDocumentationPrerequisiteImage Download LinksLimitationsSupported PlatformsLicense RequirementsTopologyStep-By-Step ConfigurationConfigure Virtual ServiceActivate the virtual service and configure guest IPsConfiguring UTD (Service Plane)Configurin...
Login to the FXOS chassis manager.
Direct your browser to https://hostname/, and log-in using the user-name and password.
Go to Help > About and check the current version:
Check the current version availa...
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...