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14.5 Installing a SCSI Hard Disk

When installing and configuring a SCSI hard disk, use the following guidelines:

  • If possible, avoid mixing different types of SCSI devices on the same bus. For example, if your system has an Ultra160 SCSI hard disk and Ultra-SCSI CD-ROM, CD-RW, and tape drives installed, put the fast hard disk on its own SCSI bus and install the slower SCSI devices on a separate SCSI bus. If necessary, purchase and install an inexpensive SCSI host adapter to support the slower devices.

  • For easiest installation and configuration, use all SCAM-compliant devices. SCAM-compliant drives allow a SCAM-compliant host adapter to set the drive's SCSI ID and termination status automatically. SCAM-tolerant drives report their SCSI ID and termination status to the adapter, but you must manually change settings on the drive if SCSI ID and/or termination need to be altered. Non-SCAM drives neither report their current settings to the adapter nor allow the adapter to reset them automatically. When using non-SCAM devices, you must manually verify settings and change them as necessary.

  • Many SCSI problems are cable-related. The cables supplied with SCSI hard disks and host adapters are usually of decent quality, but we've seen some truly horrible ones. Good SCSI cables aren't cheap, and the $3 ones you find in the bin at computer stores should be avoided. We've always found Adaptec SCSI cables to be both reasonably priced and of high quality.

If you plan to boot the system from a SCSI hard disk, that disk must connect to a bootable SCSI host adapter. Inexpensive SCSI host adapters, especially those bundled with CD burners and similar SCSI devices, are usually not bootable because they are intended merely to provide an inexpensive way to connect SCSI devices to a system that boots from an ATA hard disk.

Installing a SCSI drive may be more complicated than installing an ATA drive, particularly if your drive and/or adapter is not SCAM-compliant. The following steps illustrate the general procedure for installing a SCSI hard disk with a PCI SCSI host adapter. The exact steps vary depending on which components you use.

  1. If you have not already done so, install the SCSI host adapter. To do so, turn off the system, remove the cover, and locate an available bus-mastering PCI slot. Recent systems support bus mastering on all slots. Some older systems support bus mastering on only some slots. In that case, bus-mastering slots are normally light-colored and nonbus-mastering slots are dark. Remove the slot cover for the selected slot, align the bus connector with the slot, and press down firmly to seat the adapter. Use the screw that secured the slot cover to secure the adapter. If you have a spare drive-activity indicator LED, connect it to the appropriate pins on the host adapter.

  2. If both the drive and host adapter are SCAM-compliant, proceed to Step 5. If the host adapter is SCAM-compliant but the drive is non-SCAM compliant, the system may hang if you leave SCAM enabled on the host adapter because the adapter is unable to determine current settings for the non-SCAM device. Disable SCAM on the host adapter by starting the system and running the ROM-based Setup utility for the adapter.

  3. Set SCSI IDs manually using the jumpers or switches on the adapter and drive. If the host adapter supports seven devices (plus the adapter itself), the adapter is normally configured as SCSI ID 7, leaving SCSI IDs 0 through 6 available for drives. Higher-numbered IDs have priority. ID 0 is normally reserved for the boot hard disk and ID 1 for a second hard disk. Set the hard disk jumpers for the appropriate SCSI ID, according to whether the hard disk is the primary boot drive or a secondary drive.

  4. Terminate the SCSI bus. Exactly two devices must be terminated on each SCSI bus, and these devices must be those at each end of the bus, as follows:

    • If the SCSI adapter has only internal devices attached to it, the adapter itself and the final device on the internal SCSI chain must be terminated.

    • If the SCSI adapter has only external devices attached to it, the adapter itself and the final device on the external SCSI chain must be terminated.

    • If the SCSI adapter has both internal and external devices attached to it, do not terminate the SCSI adapter itself. Instead, terminate the final device attached to the internal chain and the final device attached to the external chain.

    SCAM-compliant SCSI host adapters detect terminated SCSI devices on the bus and set their own termination status automatically. On Adaptec models, which we recommend exclusively, this option can be enabled or disabled by using SCSISelect to set Host Adapter Termination to AutoTerm, which is the default setting. Also note that some internal SCSI cables have a built-in terminator at the end of the cable. If you use such a cable, make sure that termination is disabled on all drives connected to that cable.

  5. Once SCSI ID and termination are configured correctly, physically install the drive and connect the cables. Most adapters are supplied with a standard two-device cable. If you need to connect more than two drives, replace the cable before proceeding. Otherwise, connect the cable to each drive, making sure to align Pin 1 on the cable (indicated by a red stripe) with Pin 1 on each device (indicated by a small number, triangle, or dot on the connector). It doesn't matter which drive connects to which cable position, so mix and match drives and cable positions in whatever way makes it easiest to route the cable. Don't forget to connect the power cable.

  6. After verifying all settings and connections, turn on any external SCSI devices first, and then turn on the PC. If the SCSI hard disk is to be the boot drive, run CMOS Setup and verify that the entry for ATA Primary Master is set to None or Not Installed. If necessary, change it, save the new entry, and restart the system. On most systems, the PCI bus assigns IRQs and port addresses automatically. If your system requires setting PCI bus parameters manually, do so during this restart, using the system or motherboard documentation for guidance. Save the new settings and restart the system again.

  7. The SCSI BIOS displays its own splash screen while initializing, which normally displays adapter and BIOS information and a list of installed SCSI devices. Ordinarily, default settings are fine, but in some cases you may need to change settings to get the drive to work at all or to optimize its performance. If this is the case for your system, press whatever key sequence is needed to invoke the SCSI Setup routine and make the necessary changes, as recommended by the documentation for the host adapter and/or drive.

  8. Once the drive is installed and recognized by the system, use the operating system to partition and format the drive.

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