Any SCSI drive connected to a supported controller is supported.
The following proprietary CDROM interfaces are also supported:
Mitsumi LU002 (8bit), LU005 (16bit) and FX001D (16bit 2x Speed).
Sony CDU 31/33A
Sound Blaster Non-SCSI CDROM
ATAPI compatible IDE CDROMs
All non-SCSI cards are known to be extremely slow compared to SCSI drives, and some ATAPI CDROMs may not work.
As of 2.2 the FreeBSD CDROM from the FreeBSD Mall supports booting directly from the CD.