[cctalk] What was this AT&T SCSI enclosure for?

[Andrew B via cctalk]

I have an AT&T branded SCSI enclosure. Two half-height bays with the
drives held vertically (on their sides), with a door that opens to
expose one for a tape drive, activity lights labeled hard drive and
tape, CN50 connectors, the AT&T beige and brown
color scheme I associate with 3B's and 6300 PCs. No model number. 
Anyone have any idea what this was made for?