Booting UCS C from FlexFlash

We installed a few UCS C220M3s the other day and opted to boot from the 16GB FlexFlash SD card.  The confusing part of the FlexFlash is that it’s broken down into four partitions:

SCU — The server can access the Cisco UCS Server Configuration Utility.
Drivers — The server can access the Cisco drivers.
HV — The server can access a user-installed hypervisor.
HUU — The server can access the Cisco Host Upgrade Utility.

We want to boot from the hypervisor (HV) partition since we had just installed VMware ESXi to it.  Upon boot, the UCS kept booting into the Host Upgrade Utility (HUU) and wanted to update the firmware.  After some digging, I realized that we needed to disable the other partitions as being options to boot from.  For this, you’ll have to enter the BIOS of the server (F2 at startup) and navigate to this menu:

Just disable all the boot options except for HV and you’ll be back in business in no time.  Now that was intuitive!