You can monitor the Dell PowerVault TL4000 Tape Library using the Nagios check_snmp plugin. After setting the TL4000 to accept SNMP connections on v2 SNMP you can run the following command below. This queries for the status of the library as a rollup.

So this will query the tape library on the IP address and return the status as a number. 3 = OK, anything we want to know about so using the -r expression means you can enter a regex expression. This is a simple one, if its not 3, its not OK and we want Nagios to report an error!