VOICE Home Page: http://www.os2voice.org
|By Per Johansson© June 2003|
This article is about my personal experience of using SCSI devices on my computer.
I'm more of a software than a hardware person, but sometimes it's fun to try new
hardware stuff. Although I'm an OS/2 user, most of my work is platform-agnostic,
and most of my OS/2-specific knowledge is about making this and that hardware and
software work. My profession is software developer.
I will keep this short, since SCSI is written about elsewhere, for instance at
Newsletter March 2002) and Gary Field's SCSI
SCSI means "Small Computer System Interface" and is a set of
standards for connecting devices to your computer via a standard hardware
interface, which uses standard SCSI commands. Lately, SCSI has become less important
for the average user since external devices such as scanners often use the USB interface
and internal CD-writers, that formerly required a SCSI connection, now run happily
on the IDE (
ATA) bus, which is what PC hard disks usually are connected to.
However, as an OS/2 user, there's no choice but SCSI if you want to use a scanner
(Lately, Tame/2 has begun to
provide USB scanner support).
SCSI advantages include up to 7 or 15 devices on a bus (as opposed to IDE's 2
devices), speed and quality of the device.
SCSI devices mean extra cost, but it can be kept down by getting devices from
internet auction sites such as eBay. Doing this has worked fine for me so far.
My first entry into the world of SCSI was in late 2000, when I thought I was
in need of a scanner. I chose the Umax
Astra 2200 model, partly because it had both a SCSI and a USB interface. Also,
it was relatively inexpensive, as the model was being phased out. Unfortunately,
USB seemed to be the default connection, so there was a USB but no SCSI cable included.
You also need to get a SCSI adapter (an expansion card), unless your motherboard
has SCSI built in, which is rare. Here in Sweden, the retailers mainly stock adapters
from Adaptec (expensive) and Tekram
(sometimes less expensive). Now, connectors on SCSI adapters are either 50-pin or
68-pin (a.k.a. Wide). Modern hard disks use 68-pin, while devices like DVD players
and CD writers use 50-pin. Scanners usually have 25-pin connectors ("The Apple
kludge"). There are also 80-pin (SCA) connectors, for high-end devices, of
little interest for a home user.
I won't go into details about the different connectors and SCSI versions. See
above links, Storage
Review and Adaptec
for more info.
I went for the cheapest adapter I could find, the Tekram
DC-395U with an external and an internal 50-pin connector. Since I thought I'd
be using it with the scanner only, I looked for an adapter with a 25-pin connector,
but such animals were not to be found. I also bought a cable with 50 pins on one
end and 25 pins on the other (there's also the possibility to use a 50-25 converter).
Finally, I bought a passive terminator. SCSI buses need to be terminated in both
ends either by a device or by a terminator. The adapter would terminate one end,
but the scanner provided no termination, hence the need to get the terminator.
Another thing to do with the SCSI adapter is known as "flash the BIOS",
meaning that you download the latest BIOS from the manufacturer and install it on
the adapter. The reason for this is to have more features and less bugs. This is
usually done while booted from DOS and using a special flash program. This can also
make the adapter unusable if something goes wrong, such as a power blackout during
the flashing. But we need some adventures and excitement in our lives, don't we?
So I flashed the BIOS to the latest version on all adapters.
Installing the Tekram DC-395U SCSI adapter just means putting the OS/2 driver
in the \os2\boot directory and adding the line basedev=trm3x5.add
to config.sys. Same with other adapters, just add the pertinent driver
for your make/model SCSI adapter.
This scanner worked fine when I had installed the software, which I bought from
CFM, since the included software didn't... well,
you know. CFM's OS/2 development seems to have come to an end so better look elsewhere
for drivers now.
One year later, I thought I needed a bigger hard disk, and it would be a good
idea to buy a SCSI one. These are two or three times as expensive as IDE hard disks,
but who cares? I bought a less expensive one, IBM
Ultrastar 36LP. It was now I discovered that current hard disks all had 68-pin
connectors, so another SCSI adapter was needed. I had no objections to Tekram, so
I bought the DC-395UW,
which is similar to the other one, except that there's also an internal 68-pin connector.
Again, this disk had no termination, so I bought an active terminator. Active ones
are better than passive ones, and I thought it would be the better choice with a
hard disk on the bus. The power line on the bus cable may be too weak (that is what
the passive terminators use), especially for longer cables.
Now a problem: this SCSI adapter could see only 8 Gbyte of the hard disk! Flashing
its BIOS didn't help, and no newer OS/2 driver was available. This is a known problem
and there's nothing to do about it. I guess I should have returned this useless
adapter to the retailer, but I kept it anyway for some reason.
I looked through the newsgroup discussions about good and inexpensive SCSI adapters,
and now opted for the Tekram
DC390F. It had a Symbios SYM53C875 chip, not a Tekram chip like the others.
It would use the tmscsiw.add driver. Unfortunately, this driver consistently
failed to load. However, there's a fallback driver, the sym8xx.add from
Symbios, now LSI Logic. This one loaded fine,
but a new problem struck: I could not boot from the hard disk! I spent some days
rearranging the hardware and the load order in config.sys, but the boot always halted
at "something".dmd. I asked at Usenet, and learned more than
I thought I'd ever need about the OS/2 boot process, but to no avail. No help from
Tekram either, and the support at LSI Logic just replied that their driver wouldn't
support the Tekram adapter, and I would have to use the Tekram driver. To this day,
I haven't resolved this problem.
I kept a boot volume on the old IDE disk, and moved the other volumes to the
SCSI disk. I always separate the volumes like that anyway.
The DC390F's external connector is a 68-pin as opposed to the other adapters'
Next, I figured I had to get a DVD player. The only relatively inexpensive SCSI
one I could find was the Pioneer
DVD-305S. It has a 50-pin connector so it can't be connected to the same cable
as the hard disk (it can with a converter, but it's probably better avoided). Furthermore,
on a single channel adapter, one can't connect to all three connectors of the adapter
at the same time, due to the SCSI topology. Since the scanner, the hard disk and
the DVD player were on three different cables, this meant that I had to bring the
old DC-395UW adapter back into action. It soon turned out that connecting the DVD
player to that adapter wasn't a good idea. The system would trap at any time when
the player swung into action. The safe configuration seemed to be having the hard
disk and the DVD player on the DC390F adapter and the scanner on the DC-395UW adapter.
Fortunately, the player had termination built-in, so another terminator wasn't necessary.
The next move was to bring a CD-writer into the mix. I use it mainly for backups
onto CD-RW and transporting data (and eComStation betas!). By now, I had finally
learned how to use internet auction sites, and I guessed I could get a cheap device
there. It happened to be a Lite-On brand, which turned out to be another mistake
as it wouldn't work with the RSJ CD Writer software!
RSJ support told me that they were aware of the problem, but had no solution for
now. So I got rid of this device and got myself an HP
CD-Writer+ 9200 1.0c. It works, but can only be flash upgraded using Windows
9x! (Many hardware devices can be flashed, not just SCSI adapters)
One SCSI-unrelated fact I wasn't aware of at the time is that these old CD-writers
write to CD-RW at 4x speed only, while newer ones write at 12x. They use different
discs too. This means that my backups take longer time than necessary. On the other
hand, next step is probably to get a DVD-writer anyway.
Finally, I felt the need to get rid of the IDE hard disk that was needed for
booting OS/2 (but not DOS or Windows). I had enough of Tekram's offerings (although
other people are happy with their products, except the 395 series that no one seems
willing to defend) and I wanted an Adaptec adapter. I decided to go for the newer
Ultra160 ones, the 29160 or 29160N.
I was inspired by the article Adventures
in Adaptec U160+ Land in the December 2000 VOICE newsletter. I found a 29160N
at the QXL Sweden auction site. I was a bit nervous since I had read warnings that
adapters may not work and may not be able to be flashed. Anyway, I got the
adapter, and it looked like a standard adapter. I flashed it with the latest BIOS,
and installed it with the aicu160.add driver.
Unlike the Tekram adapters, it warned me that the cable with the CD-writer and
DVD-player was badly terminated, and yes, both devices had their termination turned
on which shouldn't be the case! After verifying that the adapter worked, I backed
up the contents of the SCSI hard disk, moved the cable from the Tekram to the Adaptec
adapter, and did a low-level format. This is recommended when you change to another
adapter, but I don't know if it was necessary. Then, I restored the backups, and
moved the boot volume from the IDE hard disk using DFSee.
And now, I could boot from the SCSI hard disk! Soon thereafter, the IDE hard disk
was removed along with the IDE drivers.
There's one more thing to do: the Adaptec adapter and the hard disk can operate
mode, but they will need a special cable and terminator for that.
The SCSI devices show up like this. The first four images are real screenshots
from a digital camera, so I apologise for the quality.
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