SCSI CABLING


<peck_d@bellsouth.net>

I noticed a couple of members of the list were configuring scsi scanners... I though now would be a good time to post some does and dont's regarding scsi technology along with some other helpful info:

1.) Always be sure both ends of the scsi bus are terminated.

2.) Each scsi device must have it's own unique id.

3.) Always use active terminators when and where possible.

4.) Make sure termination power is supplied by at least one scsi device on the
bus.

5.) Never make a scsi bus longer than the fastest device in the chain will
allow:

a.) 6 meters for scsi-1 sync (5mhz)
b.) 3 meters for scsi-2 fast (10mhz)
c.) 1.5 meters for scsi-3 ultra fast (20mhz)
d.) 20 meters for scsi-4 ultra2 fast-40 (40mhz) This standard should
never be used on the same bus as other scsi standards... ie:
scsi-1, scsi2 or scsi-3

6.) Remember, the scsi bus is only as fast as the slowest device on the bus.
(Think about this... It makes good old fashioned common sense...) *regardless*
of what anybody has told you. Here we are talking about data transfer rate
between scsi devices. Not the read speed of a device such as a cdrom. Therefore,
if you mix and match scsi devices that are of different scsi standards... ie:
scsi-1 and scsi-2, the scsi-2 devices will default to the transfer speed of the
scsi-1 devices. This is not a function of the scsi standard and scsi-2 drives do
not default to the scsi-1 standard, but a function of the technology that is
used in the individual drives. For instance, scsi-1 drives read, write, seek,
buffer as well as everything else they do at a much slower rate than a scsi-2
drive. The technology in a scsi-2 drive is newer, faster and better than the
technology in a scsi-1 drive.

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