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SCSI bus configuration tips
(KB # D8F6E3FB)

Improper bus configuration or bad cables are by far the most likely culprits when facing issues such as:

  • Devices not being seen in the operating system.
  • Intermittent or unexpected "I/O" errors.
  • Losing communication with a tape drive during backup.
  • Event ID 9 or 11 errors in Windows.
  • Unexpected bus resets.
  • Parity errors.

If your tape drive is not being detected by the operating system, or if the system is experiencing unstable operation, try the following items.

Don't mix devices of different SCSI interface types. The Host Bus Adaptor, the SCSI terminator, and all SCSI peripherals attached to a SCSI bus should be of the same SCSI type. The SCSI interface types are High Voltage Differential (HVD), Low Voltage Differential (LVD), and single-ended.

  • High Voltage Differential (HVD) devices should never be connected to a SCSI bus with either single-ended or Low Voltage Differential (LVD) devices.
  • In theory it's ok to mix multimode Low Voltage Differential (LVD) and single-ended devices. By doing so, however, all devices will run in single-ended mode. Shorter cable length requirements for the single-ended bus must be met. Also, single-ended transfer rates are slower. This could become a transfer bottleneck in your system, decreasing the speed at which data can be transferred to and from your tape drives.
    Warning: Because of the high risk of SCSI bus stability issues, Tandberg Data does not support the use of an LVD library connected to a single-ended bus. For optimum performance and stability, only connect LVD devices to an LVD bus.

Check that total SCSI cable length does not exceed limits. Using cables which are longer than the required limits will result in unstable operation. For more information, see the Knowledge Base item What is the maximum SCSI cable length I can use with my tape drive, autoloader or library?

Terminate both physical ends of the SCSI bus. The terminator's job is to closely match the impedance of the SCSI bus cable to prevent the signals from reflecting back down the cable. Without termination, reflected signals will cause line noise problems and possible data errors. For more information, see the Knowledge Base item What kind of termination do I need on my SCSI bus?

Make sure that all devices are at unique SCSI IDs. The Host Bus Adaptor and any peripherals attached to the SCSI bus must all be set to unique SCSI IDs. (The terminator does not use a SCSI ID.)

Check that there are no bent pins at any cable connectors. If any of the cable pins are bent, unstable operation will result.

Check that all SCSI connectors are well seated. Make sure that all cables are well-seated, whether they are external cables or internal to the server. Some external cables are heavy and stiff and may pull away from the device after initially being connected. For wide cables, make sure that the cable jack screws are completely screwed into the device.

Check that the SCSI cables are of good quality. Not all cables are created equally, and poor quality cables will result in unstable operation. If you have provided the SCSI cables for your system, make sure that they meet the minimum requirements as specified in your Tandberg Data Product Manual.

Try another cable. Even a "trusted" cable which worked in one situation may prove to be the root cause of problems later on.

Check that the SCSI controller card is well seated. If your SCSI controller is a card installed in your system, make sure that it is well-seated and secured in the system slot. You may want to try moving it to another available slot.

Make sure that a device driver is installed for the SCSI controller. Refer to the installation instructions for your SCSI controller for specifics about a device driver for your operating system.

Do not connect the tape drive, autoloader or library to a SCSI RAID controller. SCSI RAID controllers are manufactured with hard disks as the primary target type. These controllers may not fully support commands and responses for SCSI tape drives, autoloaders and libraries.

Try connecting only the tape drive or library to the bus. Remove as many SCSI devices from the bus as possible. After confirming stable operation, add other devices one at a time, each time confirming stable operation.

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