Example:

Device Name  : "-"
Passthru Name: "/dev/sg3"
Volume Header: ""
Port: -1; Bus: -1; Target: -1; LUN: -1
Inquiry    : "STK     T9940B          1.36"
Vendor ID  : "STK     "
Product ID : "T9940B          "
Product Rev: "1.36"
Serial Number: "479002024500"
WWN          : ""
WWN Id Type  : 0
Device Identifier: ""
Device Type    : SDT_TAPE
NetBackup Drive Type: 10
Removable      : Yes
Device Supports: SCSI-3
Flags : 0x0
Reason: 0x10000



Troubleshooting:

# mt -f /dev/nst1 status
mt: /dev/nst1: Input/output error
# mt -f /dev/nst2 status
mt: /dev/nst2: Input/output error


lsmod |grep -w st
st                    148640  0
scsi_mod              291816  13


Solution:  As long as the st module is running. This is a Fibre communication issue . Recommendation is Reboot the Server