When you cannot see a tape library being discovered from SNC, you should see an entry from the discover.log for the library from sm_device_info.py.

#From /var/www/html/connect/logs/discover.log

          start - sm_device_info.py
                                library - cx-i500, type - Scalar i500, drives - 3, slots - 2
                        stop  - sm_device_info.py - 0.3160 seconds
 

Running the scipt can you tell you more details.

#Secondar Node

[root@cx-node2 ~]# /opt/quantum/connector/plugins/system/sm_device_info.py
{
  "success" : false,
  "msg" : "storagedestinations resource is not available on the secondary HA node",
  "size" : 0,
  "storagedestinations" : [ { } ]
}
[root@cx-node2 ~]#
 

#Primary Node

[root@cx-node1 ~]# /opt/quantum/connector/plugins/system/sm_device_info.py
{
  "success" : true,
  "msg" : "Found 1 Storage Destination",
  "size" : 1,
  "storagedestinations" : [ {
    "library" : [ {
      "name" : "cx-i500",
      "libraryid" : "1",
      "type" : "SCSI",
      "productid" : "Scalar i500",
      "serialnumber" : "ADICA0C0164B03_LLA",
      "revision" : "'648G'",
      "devicepath" : "/dev/sg92",
      "state" : "Online",
      "drivestate" : "Online",
      "slotcount" : "41",
      "drivecount" : "3",
      "mediacount" : "3",
      "slot" : [ {
        "mediatype" : "LTOW",
        "count" : "41"
      }, {
        "mediatype" : "LTO",
        "count" : "41"
      } ],
      "drive" : [ {
        "driveid" : "1",
        "slotid" : "d256l0",
        "useralias" : "cx-i500_dr1",
        "devicepath" : "/dev/sg62",
        "serialnumber" : "F3A276509C",
        "productid" : "Ultrium 6-SCSI",
        "drivetype" : "LTO",
        "mediatype" : "LTO",
        "revision" : "'J3RZ'",
        "state" : "Online",
        "usable" : "true",
        "errorcount" : "0",
        "mountcount" : "0"
      }, {
        "driveid" : "2",
        "slotid" : "d258l0",
        "useralias" : "cx-i500_dr2",
        "devicepath" : "/dev/sg93",
        "serialnumber" : "F3A2765004",
        "productid" : "Ultrium 6-SCSI",
        "drivetype" : "LTO",
        "mediatype" : "LTO",
        "revision" : "'J3RZ'",
        "state" : "Online",
        "usable" : "true",
        "errorcount" : "0",
        "mountcount" : "0"
      }, {
        "driveid" : "3",
        "slotid" : "d257l0",
        "useralias" : "cx-i500_dr3",
        "devicepath" : "/dev/sg91",
        "serialnumber" : "F3A2765000",
        "productid" : "Ultrium 6-SCSI",
        "drivetype" : "LTO",
        "mediatype" : "LTO",
        "revision" : "'J3RZ'",
        "state" : "Online",
        "usable" : "true",
        "errorcount" : "0",
        "mountcount" : "0"
      } ]
    } ]
  }, {
    "sdisk" : [ { } ]
  }, {
    "lattus-sm" : [ { } ]
  }, {
    "lattus-snpd" : [ { } ]
  } ]
}
 

Using the API will show you the json object as well.