The Intel� Server Board S5520UR — Spares, parts list, and configuration guide says that comes with:
Active cable-less Midplane2 board with 8-port LSI 1078 SAS controller upgradeable to HW RAID mode
The drivers for that are on Intel Download Center under 'Intel® Server Board S5520UR'. You probably want the
Intel® IT/IR Entry Hardware RAID driver for Windows* if you haven't added the optional RAID key AXXRAKSAS2, and are running Windows.
That was it. Thanks for the help!