The 3U Rack-Mount Kit is 5 of 6 Ro HS compliant & holds up to two full-height SCSI only internal tape drives, four SCSI only half-height tape drives, or a combination of one full-height & two half-height tape drives. This enclosure supports a wide range of tape technologies, including DAT, DLT VS, SDLT, & Ultrium, with a maximum capacity of 1.6 TB using two Ultrium 960 drives or four Ultrium 448 drives (assuming 2:1data compression). The enclosure can support up to four separate SCSI buses, allowing tape drives to be configured for best performance (Ultra 160 or greater drives require cable option kit DWO63B (sold separately) when configuring 4 half-height drives)