A BA350 is a StorageWorks shelf. It has a total of 8 slots, one of which MUST be used for a power SBB (System Building Block), and a second that can be used for one. The second power slot and the remaining 6 slots can be used for drive SBB's, which are typically one slot Hard Drives, but can also be CD-ROM's and DLT drives (both 3 slot I believe, and I don't think there is a 8mm tape option), or a 1 slot 4mm tape drive. Unfortunatly all I've got are disks. The BA350 shelf is Narrow SCSI, there is also a BA356 which is wide SCSI and has an additional model where the cables plug in that takes a 'personality model', this dictates if the shelf is Narrow or Wide.

That's just the single shelf config's. There are also shelves that take things such as a HSZ50 which plugs into a SCSI DIFF card and can do RAID and stuff, or another HSsomething that plugs into a DSSI bus.