Macintosh bootable volumes are supported on the internal 2-port PCI card (part number TSATA) but are not supported on any of the other SATA cards at this time.
When attempting to connect a Sonnet Tempo eSATA locking cable to a Tempo SATA E4P card in an Xserve, the locking connector housing may not fit in the tight space at the rear of the Xserve. To properly connect the cable, simply remove the locking housing from the connector end (two screws) and it will fit.