I would suggest first checking that you have the latest version of the RAID controller firmware.
You can download the latest firmware version from the link below. There are several controller options, but you dont state which you have installed. All four options are available from this link.
http://support.euro.dell.com/support/downloads/driverslist.aspx?os=WS8R2&catid=-1&dateid=-1&impid=-1&osl=EN&typeid=-1&formatid=-1&servicetag=&SystemID=PWE_PNT_P3C_2850&hidos=WNET&hidlang=en&TabIndex=&scanSupported=False&scanConsent=False