The Fusion D400Q and R400Q must have a hard drive in drive bay 1 when connected via USB, FireWire, or FireWire 800. This requirement is due to the Oxford bridge chip that controls USB and FireWire connectons. Drive bay 1 is the top bay in the Fusion D400Q and the left bay in the Fusion R400Q. As long as there is a drive in drive bay 1, bays 2-4 are unconstrained.
Note: This requirement does not apply to a direct SATA connection, which has no drive bay population requirements.
You are using a SATA port that is not port-multiplier aware. For example, the internal SATA ports in a Mac Pro that may be brought to the PCIe rear panel via an eSATA extender cable are not port-multiplier aware. All of Sonnet's Tempo SATA cards with external ports are port-multiplier aware.
