Hi,
second management module is not supported if using VSF. Compare Documentation/Guides, VSF section, operational notes/restrictions.
The second module in a switch will be deaktivated, if VSF is configured.
Out of the top of my head: No failover to second MM if primary dies. Instead of this failover to VSF secondary.
But I did my last test for this a long time ago at the time VSF got available for 5400 first time.
Maybe a reboot brings second MM of the switch into active state..
But thats not a "fast" failover.
Regards, Jö