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One of the primary advantages that SCSI has over IDE is the ability to have more than 2 devices per channel and the ability to have more than one device active on the channel at once, which paves the way for extremely fast hard drive configurations like RAID. RAID is an acronym for Redundant Array of Inexpensive Disks (some say independent disks - this is not correct, see Adaptec's Array Guide). In this tutorial I'll show you how to build and install a fairly inexpensive (comparatively) 4 drive array made possible by two factors - 1) The 8600/9600 has a removable mounting plate in the base of the cabinet that allows mounting two drives and 2) ProLine has a fan and bracket kit that allows two more drives to be mounted over the stock 2 drive baseplate.
The ProLine bracket kit contains 4 fans to cool the drives and the 8600's 390 Watt power supply has the headroom to handle 4 added drives. This kit will also fit the 9600, but you won't be able to use the lower 3 PCI slots in the 9600. The 171 Watt power supply and limited expansion room of the Apple G3 systems make this impossible.
Internal arrays allow huge cost savings by eliminating the need for a external case and cabling. Often times the case and cabling can cost as much as two disk drives. The drawback is flexibility, as the external array can be moved and used with other machines. Keep in mind that if all you need is a 4 GB RAID volume, you could use low-cost 1 GB drives. I used Quantum Viking 2.2 GB drives for this project, a good compromise between cost and performance.
A summary of what is needed for this project:
For a primer on understanding RAID, see Adaptec's Array Guide.
|Step 1: Jumpering the 4 Drives|
Once the drives are mounted on the baseplate you can't change the jumper settings without disassembling the array - so it's very important to ensure that all 4 drives are properly set for ID and Termination. Observing static precautions (wrist strap recommended) lay your 4 drives out on a clean work surface and you may want to place a small piece of masking tape on top of each drive, labelling them 1 - 4. For this article drive 1 will be the last drive attached to the cable. That position is the lower right drive of the final assembled array. The diagram below illustrates the drive ordering and jumpering as you would view it from the final assembled kit, drive connectors facing you.
Drive SCSI ID Jumper Settings:
For SCSI ID, the diagram shows which ID pins on the drive (often called A1,A2,A3) have jumpers installed. Often wide SCSI drives have the capability to have IDs as high as 15, but that is not needed, and I believe in the KISS principle (Keep It Simple Stupid). The location on the ID and Termination Enable pins will vary by drive type, but once you locate them the diagram above shows you which pins to install jumpers on to obtain the indicated ID. SCSI ID jumpers are a binary code, positions 1 = bit 1 (value of 1) - if a jumper is placed on this set of pins you enabled a 1, ID pin set 2 is bit 2, (value of 2) so a jumper placed there is equal to a 2, ID pin set 3 is bit 3 (value of 4) so a jumper there would be ID 4. The jumpers are additive, so jumpers on 1 and 2 would set the drive to ID 3 (1+2=3). No jumpers on any ID pins is ID 0.
Drive SCSI Termination:
If your drive did not come with documentation and you can't find any data at their web site (i.e. Micropolis) then check the Blue Planet site which claims to have jumper settings for every drive ever made.
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