In original FC-AL based SANs, tape and disk traffic had to be on separate adapters due to SCSI bus resets being generated by the tape subsystems, which affected disk based I/O.
In today's environments, using switches and Fibre to SCSI bridges, the tape traffic no longer affects disk traffic, due to a switched fabrics point to point nature. Connection to both tape and disk can now be provided over a single adapter, or dual adapters for performance/fail over capability. I would recommend using two adapters for availability, and perform backup over one adapter while production is up on the other. This would allow the data to stream more effectively to tape, while not impacting production.
This was first published in April 2001