MFI driver is loaded on Dell System with PERC H730P host adapters. This is the incorrect driver. It should load the MRSAS driver instead.
While the MFI driver works in some cases, it will not work correctly if the adapter is in HBA mode and causes the system to panic if a raid0 with only one drive is present.
After much research, this bug has existed at least since 10.3-RELEASE.
As a temporary fix, add hw.mfi.mrsas_enable="1" to /boot/loader.conf
man 4 mrsas for details