Library and Drives may be working fine, however within the logs there may be several "Command failed, re-initializing driver" warnings.
Viewing "More info" from these errors may list entries as:
Check for 'HARDWARE\DEVICEMAP\SCSI\SCSI Port#\SCSI Bus #\Target ID #\Logical Unit ID #'
If the entries share the same Port, Bus and Target ID but display a different Logical Unit ID like below. A SAS Y-Cable may be in use rather than a traditional SAS Cable:
Check for 'HARDWARE\DEVICEMAP\SCSI\SCSI Port2\SCSI Bus 0\Target ID 6\Logical Unit ID 0'
Check for 'HARDWARE\DEVICEMAP\SCSI\SCSI Port2\SCSI Bus 0\Target ID 6\Logical Unit ID 1'
Dell TL series use a SAS Y-Cable to connect two drives on a single iSCSI Bridge, since the iSCSI Bridge has only one port and the TL chassis does not have enough space to have one iSCSI Bridge per Drive. The iSCSI Bridge knows how to manage two drives through the same port, whereas most of the SAS HBA's don't.