SCSI Troubleshooting

When you are installing a chain of devices on a single SCSI bus, the installation can get complicated very quickly. If you have a problem during installation, check these items first:

  • Make sure you are using the latest BIOS from your motherboard manufacturer. Some have had problems with their PCI bus slots not working properly.

  • Make sure that all SCSI devices attached to the bus are powered on.

  • Make sure all SCSI cables and power cables are properly connected. Try removing and reseating all the connectors to be sure.

  • Check that the host adapter and each device on each SCSI bus channel have a unique SCSI ID setting.

  • Make sure the SCSI bus is terminated properly. Remember there should be only two terminators on the bus, one at each end. All other terminations should be removed or disabled.

  • If your system BIOS setup has settings for controlling PCI bus configuration, make sure the PCI slot containing the SCSI adapter is configured for an available interrupt. If your system is Plug and Play, use the Windows Device Manager to check and possibly change the resource configuration.

  • Make sure the host adapter is installed in a PCI slot that supports bus mastering. Some older motherboards (mainly old 486 processor boards) did not allow bus mastering to work in all PCI slots. Check your motherboard documentation and try moving the SCSI host adapter to a different PCI slot. This should not be an issue on any Pentium or newer boards.

  • If you have a SCSI hard disk installed and your system will not boot from the SCSI drive, there can be several causes for this problem. Note that if both SCSI and non-SCSI disk drives are installed in your computer, in almost all cases the non-SCSI drive is the boot device.

If you want to boot from a SCSI drive, check the boot sequence configuration in your BIOS. If your system allows it, change the boot sequence to allow SCSI devices to boot first. If not, try removing the non-SCSI drives from your system.

If the system has only SCSI disk drives and still won't boot, check the following items:

  • Be sure your computer's BIOS Setup drive configuration is set to "No Drives Installed." The PC BIOS supports only ATA (also called IDE) drives; by setting this to no drives, the system will then try to boot from another device, such as SCSI.

  • Make sure the drive is partitioned and that a primary partition exists. Use FDISK from DOS or Windows 9x/Me or the Windows Disk Management tool in Windows 2000/XP to check.

  • Make sure the boot partition of the boot hard disk is set to active. This can be checked or changed with the FDISK or Disk Management program.

  • Finally as a last resort, you can try backing up all data on the SCSI hard disk and then perform a low-level format with the Format utility built in to or included with the host adapter.

Here are some tips for getting your setup to function quickly and efficiently:

  • Start by adding one device at a time. Rather than plugging numerous peripherals into a single SCSI card and then trying to configure them at the same time, start by installing the host adapter and a single hard disk. Then, you can continue installing devices one at a time, checking to ensure that everything works before moving on.

  • Keep good documentation. When you add a SCSI peripheral, write down the SCSI ID address and any other switch and jumper settings, such as SCSI Parity, Terminator Power, and Delayed or Remote Start.

For the host adapter, record the BIOS addresses, Interrupt, DMA channel, and I/O Port addresses used by the adapter, and any other jumper or configuration settings (such as termination) that might be important to know later.

If you use the System Configuration Template to record information about your system, attach the SCSI information sheet to the System Configuration Template to provide more complete information about your system.

  • Use proper termination. Each end of the bus must be terminated, preferably with active or forced perfect terminators. If you are using any Fast SCSI-2 device, you must use active terminators rather than the cheaper passive types. Even with standard (slow) SCSI devices, active termination is highly recommended.

If you have only internal or external devices on the bus, the host adapter and last device on the chain should be terminated. If you have external and internal devices on the chain, you generally will terminate the first and last of these devices but not the SCSI host adapter (which is in the middle of the bus).

  • Use high-quality shielded SCSI cables. Be sure your cable connectors match your devices. Use high-quality shielded cables, and observe the SCSI bus-length limitations. Use cables designed for SCSI use, and, if possible, stick to the same brand of cable throughout a single SCSI bus.

Different brands of cables have different impedance values; this situation sometimes causes problems, especially in long or high-speed SCSI implementations.

Following these simple tips will help minimize problems and leave you with a trouble-free SCSI installation.