After Apple released Apple Mac Pro EFI Firmware v1.3 on 3/27/08, the Sonnet Tempo SATA E2P card no longer worked in slot 2 of the Mac Pro Early 2008 Model 3,1. Slot 2 is a x16 PCIe 2.0 slot. The solution is to move the Tempo SATA E2P card to either slot 3 or 4, which are x4 PCIe 1.1 slots. The Tempo SATA E2P card works fine in the PCIe 2.0 slots in the Mac Pro (Early 2009) Model 4,1.
Sonnet has tested the following cards with the Drobo S:
Tempo SATA E2P..............................compatible
Tempo SATA E4P..............................not compatible
Tempo SATA ExpressCard/34...........compatible
Tempo SATA Edge ExpressCard/34...compatible
Tempo SATA Pro ExpressCard/34.....not compatible
Tempo SATA X4P..............................not compatible
Qio eSATA ports...............................not compatible