only one drive is visible of MSL4048 tape library

Have experienced a similar issue, where the cause of the the problem was the order of the SCSI/LUN number between the control path tape drive and robot, in our case the robot should have a higher number than the control path tape drive.

On another robot the problem was the SCSI terminators hadn't implemented on the relevant tape drives

Hope this help

Check hardware connectivity and SAN zoning. Each tape drives in MSL4048 has its own FC or SAS port. In your command outputs, only one drive(drive 1 in MSL) is visible from Solaris. Correct connectivity issue and run devfsadm to let Solaris recognize tape drives.

After tape drives become vidible from Solaris, you need to reconfigure sg driver configuration sg.build and sg.install. Check Device Configuration Guide for more detail.