ask THE SCSI EXPERT.Visit the SCSI SCSI in full Small Computer System Interface Once common standard for connecting peripheral devices (disks, modems, printers, etc.) to small and medium-sized computers. SCSI has given way to faster standards, such as Firewire and USB. Trade Association's web site (www.scsita.org) to ask the SCSI Expert a question. Q: Does an official SCSI compliance checklist for target devices exist? Does a standard compliance test procedure for target devices exist? If so, where can I find them? A: There is no official compliance test. The large system houses have purchase specifications that often go well beyond the standards. These system houses have their own sets, of tests. In most cases, all of the mandatory sections must be implemented and most system houses require several of the optional features too. Q: I need to change the SCSI initiator ID on my controller, because I'm putting two computers on the same SCSI bus for a cluster application. The drives are SCSI targets 1-6. What is the ordering of SCSI targets in order of priority when using Wide SCSI? Do targets go up to 15, or do they stop at 14? A: The SCSI IDs, in order of priority, are: 07,06, 05, 04,03, 02, 01, 00, 15, 14, 13, ..., 08. On a Narrow SCSI bus, you can only use 07 through 00. On a Wide SCSI bus, you can use IDs 15 through 00, but 07 is still the highest priority. The two controllers should be set to ID 6 and 7, the boot disk drive ID 0, the user disks ID 8-15, with ID 3 - 5 for legacy equipment; Tape, Jaz Drives ID 3, CDROM See CD-ROM. , CDRW See CD-RW. , DVD-RAM A rewritable DVD disc endorsed by the DVD Forum. Using phase change technology, DVD-RAMs are like removable hard disks, and the media can be rewritten 100,000 times compared to 1,000 times for DVD-RW and DVD+RW. The first DVD-RAM drives with a capacity of 2.6GB (single sided) or 5. ID 4, and scanners ID 5. Q: What are some examples of Low Voltage differential (hardware) Low Voltage Differential - (LVD) A method of driving SCSI cables that will be formalised in the SCSI-3 specifications. LVD uses less power than the current differential drive (HVD), is less expensive and will allow the higher speeds of Ultra-2 SCSI. LVD requires 3. devices, High Voltage differential (hardware) High Voltage Differential - (HVD) Differential SCSI scheme that has been in use for years. The terminators run on 5 Volts DC. See also LVD. Devices and Single Ended devices? A: Low Voltage differential devices are all Ultra2 SCSI and Ultra160 SCSI disk drives. Adapters such as the Adaptec AHA2930U2, AHA-2940U2W U2W Ultra 2 Wide , Adaptec SCSI Card 19160, 29160 and 39160 or equivalents are also Low Voltage differential. High Voltage differential devices include some disk drives up to Ultra SCSI speeds, tape drives, RAID boxes, and adapters such as the AHA2944UW or equivalent. Single Ended devices go up to Ultra speeds: CD-R (CD-Recordable) A writable CD technology using a type of compact disc that can be recorded, but not erased (CD-Rs are "write once" discs). CD-R discs are used to master CD-ROMs, to back up data and to make copies of data for distribution. , DVD-RAM, earlier disk drives, tape drives, scanners, Jaz, Zip and removable media drives. There are too many Single Ended adapters to count, two such examples being the Adaptec AVA-2906 and AHA-2940U or equivalent. Q: Is it possible to use a minated LVD/SE Ultra160 SCSI twisted pair ribbon cable designed for internal Ultra160 LVD See LVDS. LVD - Low Voltage Differential SCSI drives to connect an external Ultra160 LVD SCSI drive? A: Yes, it is possible to use a ribbon cable to connect external drives. However the ribbon cable is unshielded, so you may have noise problems, depending on the environment in which they are used. External cables are shielded for FCC reasons, so they will not cause noise on other equipment. I recommend that you use as short a cable as possible and only on a temporary basis. Q: I recently received error messages that said SCSI transport failed: reason timeout: retrying command' in my systems logfiles. Is the time out duration specified in a SCSI standard, or does it depend on the systems implementation (i.e. drivers)? If it is defined by the SCSI standard, how long is this time out? A: Time out depends on the drivers but it is normally a very long time. Time out usually means that there is a bus problem. Check that there is active termination on both ends of the bus and, that all other termination is disabled. Be sure to, check your cables and connectors, too. Mismatched cables can cause bus reflections that will miscount mis·count v. mis·count·ed, mis·count·ing, mis·counts v.tr. To count (something) incorrectly; miscalculate. v.intr. To make an incorrect count. n. An inaccurate count. that can hand the bus. Any single ended bus with a 25 pin connector will often have problems and hand the bus. |
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