Logo LSD SCSI FAQ

Summary: A SCSI checklist if your SCSI configuration doesn't work as expected to transfer data files between Macintosh and PC.

Introduction

You installed our program, connected the drive and it doesn't work. Sadly, SCSI is still difficult, and some call it a kind of "black magic".
Facing this kind of problems, you should follow a test procedure, described below, in this order. Don't try to run faster and don't do a low-level formatting if the problem is only the lack of terminator.
You can download our TestScsi (zipped archive, length 44 KB), an utility for exploring/testing the SCSI bus (32-bit version running under Win95/98 and NT). To check the version of the files composing the Aspi layer, download our Aspitest.
You can also visit the ASPI FAQ, since situations are often a mix of hardware and software problems.

Using the FAQ

The Table of contents below contains links to the answers given. From each answer, there is a link back to the table of contents, allowing you to navigate and find the information you are looking for.
Back to the Main FAQ Page.

Table of contents
1. Terminator check
2. Cable test
3. Transfer test
4. Media check
5. Adapter setup


Terminator check Back to ToC
"About half the trick to SCSI is getting the termination right,
and 90 percent of what's left is being sure you don't have cable problems."

Jerry Pournelle
Byte Magazine, August 1996

The quote from J. Pournelle above says it well and direct. Your first step, if your SCSI bus doesn't work as expected, is to check the termination. On a SCSI bus, you must have two terminators, one at each end of the bus. That is, if all your devices are internal, you should validate the termination on the adapter and plug a terminator on the last physical device (last physical device, and not last logical address).
Conversely, if you only have external devices, the termination should be validated on the adapter and a terminator should be plugged in on the last device. There are also devices whose termination is enabled/disabled by switches.
If you have both types of devices, the last physical internal device and the last physical external device should be terminated. The adapter termination should be disabled.

Cable test Back to ToC

You should only use good quality cables. Your cables should be short and shielded ones. The total length of the cables should not exceed ten feet. It can happen that a cable which works well with a device yields errors when used with another one. If you are installing a SCSI chain with many devices, I suggest you identify all cables with a felt marker or the like to be sure to put everything in place correctly if you happen to change some device.

Transfer test Back to ToC

If you want to be quite sure that your SCSI bus works reliably, take a very large file and copy it to the SCSI drive you want to test and back. That means two copy operations on the SCSI bus. Do a binary comparison with FC (command line: FC /B file1 file2). Files can be in different folders, but in this case you have to give the complete access path. If you get errors, you have to check everything. Disconnect all external drives but one and redo the test. You can try to swap cables. Identify the cables with a marker to be quite sure. Try better and shorter cables. When it works, begin adding the other drives, one at a time. Normally, you should be able to find out the culprit. Think that it may not be the last of the string, but the one in front.
Some users say that the scanner is always best at the end. Others say the contrary. Check yourself! With a scanner, test the quality of the SCSI bus running a scan on a color paper. Check in your favorite program that you don't have scratches, pits and other problems.

Media check Back to ToC

Are you sure that the cartridge you're trying to read is in good condition? Some adapter boards come with low-level formatting/verification software (SCSIFMT in the case of Adaptec boards). Launch a verify on the cartridge to see whether there are bad spots on the medium. You can also do a low-level format, but this destroys all the data, as you know.

Adapter setup Back to ToC

With removable media like SyQuest or the like (Zip, Bernoulli), you don't need all the bandwidth of modern SCSI adapters. With an Adaptec adapter (other brands should offer similar functions), start the setup program hitting "CTRL A" when the computer boots. In the table, disable the synch negociation for the address of the drive. Likewise, you can select a maximum data rate of 5 instead of 10. These parameters were often given on the Adaptec forum on Compuserve.

  Back to ToC

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