Improper termination can cause many problems, especially with Ultra SCSI systems. The specifications call for termination to be supplied at the ends of the SCSI bus. Many people however, frequently terminate the last physical device on the cable, sometimes allowing unused cable to hang off the end of the SCSI chain. This is not the proper method, because excess cable beyond the terminated device, longer than 0.1 meter (about 3.5 inches), constitutes a stub, and must be terminated. Also, if both internal and external cables are used, with one SCSI host adapter, then the host adapter should not be terminated, and instead, termination should be located at only the ends of the cables attached.
Two good sources of such cables and terminators are:
Granite Digital ( http://www.scsipro.com/ ) at 1-510-471-6267
TMC ( http://www.tmcscsi.com/ ) at 1-415-454-5425.