Whenever possible, connect devices to a shared bus so that they can be isolated from the bus. This allows you to disconnect devices from the bus for maintenance purposes without affecting bus termination and cluster operation. You also can set up a shared SCSI bus so that you can connect additional devices at a later time without affecting bus termination.
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With the exception of the TZ885, TZ887, TL890, TL891, and TL892, tape devices can only be installed at the end of a shared SCSI bus. These tape devices are the only supported tape devices that can be terminated externally.
We recommend that tape loaders be on a separate shared SCSI bus to allow normal shared SCSI bus termination for those shared SCSI buses without tape loaders.
Most devices have internal termination. For example, the KZPSA and KZPBA host bus adapters, BA350 and BA356 storage shelves, and the DWZZA and DWZZB SCSI bus signal converters have internal termination. Depending on how you set up a shared bus, you may have to enable or disable device termination.
Unless you are using an UltraSCSI hub, if you use a device’s internal termination to terminate a shared bus, and you disconnect the bus cable from the device, the bus will not be terminated and cluster operation will be impaired. Therefore, unless you use an UltraSCSI hub, you must use external termination, enabling you to detach the device without affecting bus termination. The use of UltraSCSI hubs with UltraSCSI devices is discussed in Section 3.5 and Section 3.6. The use of a
To be able to externally terminate a bus and connect and disconnect devices without affecting bus termination, remove the device termination and use Y cables or trilink connectors to connect a device to a shared SCSI bus.
By attaching a Y cable or trilink connector to an unterminated device, you can locate the device in the middle or at the end of the shared bus. If the device is at the end of a bus, attach an
In addition, you can attach a Y cable or a trilink connector to a properly terminated shared bus without connecting the Y cable or trilink connector to a device. If you do this, you can connect a device to the Y cable or trilink
