Check manual page of ibm_storage_ts.library
IBM Tape Library: Library Status
This check displays the device status per library, as well as the
drive count and any faults the device reports itself.
The check status will be the worst status derived from device status
and severity of the current fault (if any).
Device Status will resolve to OK if the device status is documented
as "Ok", WARN if it's "non-critical", "other" or "unknown" and
CRIT for "critical" and "non-Recoverable" status.
No fault or "informational" faults lead to status OK, "minor" faults
to WARN, "major" and "critical" faults to CRIT
One item per connected library is created.