You can install and use the Xserve RAID Card (Early 2009) only in the Xserve (Early 2009) with Mac OS X Server v10.5.6 or later.
Install and use the original Xserve RAID Card—introduced in August 2007—in the Xserve (Late 2006) and Xserve (Early 2008) with Mac OS X Server v10.4.10 or later.
The two cards are similar in appearance. To distinguish between them, refer to the part number or the EEE code at the end of the serial number on the label indicated by the arrow in the image below.
Xserve RAID Card (Early 2009): 661-5094 EEE: 2QD
Xserve RAID Card (Original): 661-4314 EEE: 0XK
You can also identify the Xserve RAID Card (Early 2009) by the presence of two additional chips (not shown) in the area indicated by the circle in the image above.
For information about hard drives supported with each version of the Xserve RAID card, see Mac Pro RAID card and Xserve RAID card Frequently Asked Questions (FAQ).