Configuring a shared SCSI bus for tape devices

Before configuring a shared SCSI bus for tape devices, please read the following carefully.

To configure tape devices on a shared SCSI bus, you must have SCSI cables, SCSI terminators, a SCSI adapter in each cluster node to provide a shared external bus between the nodes, and at least one tape device on the shared bus.

The tape devices must be connected to a bus that uses the same method of transmission that the device does (single-ended or differential). Only one transmission method can be used on a single SCSI bus, however, if the devices use different transmission methods, you can install a signal converter between the devices. A signal converter converts single-ended SCSI signals to differential SCSI signals.

Note:

You must use a signal converter to connect single-ended and differential devices in order to avoid hardware damage.

You must terminate the SCSI bus at both ends so that commands and data can be transmitted to and from all devices on the bus. Each SCSI bus must have two terminators and they must be at each end of the segment.

If a tape device is in the middle of the bus, remove any internal termination in that device.

If the tape device is at the end of the bus, and the tape device has internal termination, you can use the device’s internal termination to terminate the bus.

Figure: Example of a shared bus with tape devices at the end of the bus

Symantec Backup Exec be p0707i030 Configuring a shared SCSI bus for tape devices

Following are methods you can use to terminate a bus:

  • SCSI adapters. This method is not recommended because if the server is disconnected from the shared bus, or if there is a power supply failure, the bus may not be properly terminated and may be inoperable.

  • Pass-through (or feed-through) SCSI terminators. These can be used with SCSI adapters and with some tape devices. If the tape device is at the end of the bus, you can attach a pass-through SCSI terminator to terminate the bus. The internal terminators in the tape device must be disabled. This is a recommended method.

    Note:

    To ensure termination if a power supply failure occurs, turn off the on-board terminators on the SCSI controller (using the host adapter manufacturer’s recommended method) and physically terminate the controller with a terminator.

  • Y cables. These can be used with some tape devices. If the tape device is at the end of the bus, you can attach a terminator to one branch of a Y cable to terminate the bus. The internal terminators in the tape device must be disabled. This is a recommended method.

  • Trilink connectors. These can be used with some tape devices. If the tape device is at the end of the bus, you can attach a terminator to one of the trilink connectors to terminate the bus. The internal terminators in the tape device must be disabled. This is a recommended method.

Besides terminating the bus, Y-cables and trilink connectors also allow you to isolate the devices from the shared bus without affecting the bus termination. You can maintain or remove that device without affecting the other devices on the shared SCSI bus.

To configure a shared SCSI bus for tape devices

  1. Install the SCSI controllers for the shared SCSI bus.

    Make sure that the SCSI controllers for the shared SCSI bus are using different SCSI IDs. For example, on the controlling node, set the SCSI controller ID to 6 and on the failover node, set the SCSI controller ID to 7.

  2. Prepare the SCSI controllers for the shared SCSI bus. Refer to your SCSI host adapter manufacturer’s documentation for details.

    Do not have power on to both nodes while configuring the computers, or if both nodes have power on, do not connect the shared SCSI buses to both nodes.

  3. Connect the shared SCSI tape devices to the cable, connect the cable to both nodes, and then terminate the bus segment using one of the methods discussed in the previous section.

More Information

Two-node cluster with tape devices on a shared SCSI bus

Configuring a shared SCSI bus for tape devices