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VOICE Home Page: http://www.os2voice.org |
April 2002
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| By Eric Baerwaldt © April 2002, Translation: Philhard Ackermann, Christian Hennecke |
First some remarks concerning last month's article about SCSI basics:
I will especially be dealing with the following PC systems: First and second
generation IBM PC 350 as well as IBM PC 750, IBM PC 300 PL and IBM PC 300 XL, an
IBM PS/2 77s xTx model and an IBM PS/2 77s xNx model. The first three machines mentioned
are standard PCs having grown a little bit old already sporting Pentium CPUs and
a PCI-/ISA bus, whereas the IBM PC 300 PL and XL machines with their PII and PIII
CPUs are more modern systems, and the last two PCs mentioned which feature 80486
CPUs and MCA architecture are quite outdated, but since they have been marketed
very heavily back then, they reached high sales figures, and because of their relative
high cost and robustness they can still be found in professional environments (especially
at banks) where they are being used for special purposes. Since the two PS/2 machines
are the only ones in the list that already came with built-in SCSI systems, they
in particular offer some interesting technical options.
With the introduction of the PS/2 models 56/57 in 1992 and 76/77 in 1994 IBM
threw away all the old stuff and shipped these systems with SCSI controllers and
harddisks only, with these controllers partially being onboard solutions (PS/2 56/76
and older PS/2 57/77). In the last PS/2's 77s of the xTx series they also used controller
cards, some of them from OEM manufacturers. The server class machines of the 9595,
PC Server 320, 500, 520 and 720 series were exclusively based on SCSI subsystems.
Because of the variety of controllers with different standards that has evolved
throughout those years and the special technical characteristics of the MCA bus
there are some peculiarities to be taken into account if you consider upgrading
a machine based on the Microchannel architecture with a new harddisk or a new controller.
Basically any newer MCA machine can be upgraded with an up-to-date harddisk.
Caution is advised with newer SCSI harddisks featuring a capacity of more than 1
GB. Some older MCA systems, though hardly still being used nowadays, will refuse
to work when equipped with harddisks of more than 1 GB size due to their outdated
SCSI BIOS. This especially includes machines of the following series: 8573, Portable
P75, and older systems of the 8556/56SX und 8557/57SX type.
The more up-to-date 2nd and 3rd generation PS/2 machines (PS/2 56/57 and 76/77
as well as most PS/2 85, 90 and 95) are capable of dealing with even larger harddisks.
But even here there are some points to be taken into account: In their 2nd generation
PS/2 systems IBM introduced so-called IML systems. These systems had a small part
of their harddisks reserved for the IML code (Initial Microcode Load), which
held some parts of the machine's BIOS and thus could not be erased too easily. Systems
containing such an IML partition will only accept harddisks up to a size of 3.94
GB as the primary device. This restriction does not apply for secondary devices.
The installation of a secondary SCSI controller where harddisks of arbitrary size
(see below) can be attached to doesn't pose any problems either.
With the introduction of the 3rd generation PS/2 series in 1994 the IML partition
was replaced by a so-called service partition in all machines except for
the 56/76 models. This special partition can smoothly be duplicated to a floppy
disk. In fact this service partition contains a copy of the reference disk that
is needed by any PS/2 machine regardless of model or age and to be able to create
a duplicate of the diagnosis disk which contains some additional utilities. The
service partition can be erased from the primary harddisk. If left there, this harddisk
can again only host 3.94 GB of storage.
There are still newer SCSI controllers available for IBM-PS/2 systems. This also
applies for the successors of the PS/2 range of machines, a high grade server generation
of models 500, 520 und 720, some of which are solely based on MCA, others being
hybrid machines (PC Server 320 and 720 models always carry an MCA as well as a PCI
bus system which can be used simultaneously), where SCSI controllers as well as
SCSI RAID controllers are available for the MCA bus. In addition the PC Server 520
and 720 models offer room for up to 18 3.5" SCSI harddisks which can be swapped
in mid-operation due to the hot-plug technology integrated in those machines. Still
some not so recent MCA-based SCSI controllers pose some restrictions: when you intend
to use original IBM SCSI controllers even the oldest models can be upgraded by exchanging
two eprom chips which are available from IBM if need be. The AHA-1640 controller
by Adaptec and the VT-640 and BT-646 controllers from Bustek also need a BIOS upgrade
to be able to boot the system from a harddisk larger than 1 GB. The MCS-700 controller
by Future Domain also needs a boot BIOS v.1.1 to be able to address larger harddisks
correctly. But with all these obstacles gone IBM machines offer full SCSI functionality.
First we are going to deal with the easiest of possible SCSI configurations,
namely one of the later IBM PS/2 machines. The 9577-STG is - like any model of the
xTx series - a hybrid machine, i.e. it carries both an onboard EIDE controller and
a Fast SCSI-2 controller (or, in case of extended configurations, a Fast/Wide SCSI
or a Fast/Wide RAID controller). We won't consider the EIDE controller here as it
is a technological backstep in regard to the use of OS/2 Warp or eComStation. IBM
has built an EIDE controller into any later machine of the xTx series by default,
because all these machines are based upon a single board design, although two versions
were distributed, namely that of the more sophisticated SCSI models on one side,
and that of the less costly models of the i series without SCSI subsystem on the
other.
Configuration of such a machine with a SCSI subsystem is as easy as conceivable:
Just insert the controller into a free slot, define an ID for a harddisk using the
jumper, connect it to the controller, and copy the respective ADF file that is used
to register the controller with the system to the reference disk - ready. The SCSI
controllers that are delivered by IBM have automatic termination turned on by default,
so one doesn't have to care about activating it. The installation of OS/2 Warp also
runs through without any problems - OS/2 Warp detects the controller correctly without
difficulties.
Adding another harddisk to the same controller is as uncomplicated. Besides the
existing Fast SCSI-2 harddisk IBM DPES-31080 I have added an Ultra-3 Wide harddisk
model IBM DDYS-T09170 into the machine. For this highly modern harddisk only a suitable
interface adapter has to be used between harddisk and cable as the DDYS harddisk
comes with either a 68 pin connector or - in case of the RAID and server version
- a 80 pin SCA connector. After assignment of a unique SCSI ID the harddisk is detected
by the system without problems and - since the harddisk has automatic termination
- also terminated correctly, if it is positioned at the end of the bus. Note that
this configuration poses one potential source of error for inexperienced users:
According the to 16 bit SCSI standard the harddisk allows to define IDs between
0 and 15. But the 8 bit SCSI standard of SCSI-1 and SCSI-2 systems only allows assigning
IDs 0 to 7. Therefore also the modern harddisk must not be assigned an ID higher
than 7! As Microchannel machines use SCSI ID 7 for the controller, only SCSI IDs
0 to 6 can be selected from. If you use a Fast/Wide controller for this machine
though, these restrictions do not apply. Another obstacle in the process of configuration
of the new Ultra-3 Wide harddisk is the mode of operation, which ought to be determined
by jumper, too. The new IBM harddisks actually negotiate with the controller which
operation mode they are to use, so normally no problems should occur. If you want
to be on the safe side however, switch the harddisk's corresponding jumper to Force
SE Mode (SE means single ended) before operation starts. An incorrect adjustment,
which falsely uses the harddisk as LVD device, can lead to the electronic's destruction
because of wrong signal levels! This explicit selection of the operating mode is
only necessary, if a SCSI-2 controller is used. If the harddisk is used with an
Ultra-3 Wide controller, no manual settings are required.
If an external device is to be employed in our configuration, there have to be
no adjustments made to the internal devices as termination is done automatically
by the internal devices. In this case I have connected an external IBM 3510 CD-ROM
drive of SCSI-2 standard to the machine in addition to the two harddisks. It is
mandatory to terminate the external drive for the internal components adapt termination
at the next boot operation. Again a unique SCSI ID has to be assigned to the external
device via the turning switch.
After the addition of and setting up the listed components the following is striking:
The new DDYS-T09710 harddisk doesn't only speed-up the machine notably, but enormously.
OS/2 Warp version 4.51 took only about 30 seconds to boot until the machine was
fully operational. I have to add that the boot operation is prolonged by several
FLT drivers that have been added to CONFIG.SYS by hand and eight applications
in the System Startup folder. The old DPES-31080 harddisk needed about 80
seconds for the same boot operation. Generally, one can state that harddisk access
is dramatically faster using the new Ultra-3 Wide harddisk than using the old Fast
SCSI-2 harddisk.
Another considerable performance increase can be achieved by two software settings:
IBM usually includes technical goodies with components, but leaves them deactivated
by default for some unknown reasons. In our case that means that the SCSI controller's
"as delivered" state is to run in asynchronous mode. Under OS/2 Warp,
starting with version 3 it is possible to add a parameter /FS to the SCSI
controller's statement BASEDEV=FD16-700.ADD in CONFIG.SYS, which
switches the controller to the faster synchronous mode. By this a performance increase
of approximately 10% can be achieved, since the controller now does data transfers
in synchronous mode provided suitable components are available. Another increase
in speed can be achieved by modifying the SCSI mode pages: The SCSI mode pages define
the usual parameters for operation. Mode page 8 specifies the caching parameters.
As today's SCSI harddisks are usually equipped with a larger cache, this I/O memory
ought to be activated, i.e. turned on. Obviously word of this hasn't reached IBM's
developers yet, who build their harddisks with wonderfully large caches indeed,
but partially deactivate them. I am going to deal with the corresponding setup options
follow below.
Our example gets really interesting, if a scanner is to be operated on the same
machine. Today's SCSI scanners mostly are only capable of a restricted SCSI command
set, i.e. they mostly don't use the disconnect/reconnect command by which each component
can register and deregister itself with the bus. The result of this deficit is that
the scanner remains registered at the bus throughout the whole time of an operation
and thus blocks the other components. As a workaround for this weakness it is recommended
to use an extra SCSI controller for such slow devices. In our example, as second
controller we add an old CE Infosys cache controller to the system, besides the
existing Fast SCSI-2 controller. This second controller must not have its own BIOS
(or it has to be deactivated). In our case the BIOS-EPROM is removed manually. As
the controller does not offer automatic termination, the terminator for the external
connector has to be removed from the socket. After that the controller can be operated
in parallel to the "main controller" without problems. For OS/2 Warp it
only needs a corresponding BASEDEV-statement in CONFIG.SYS for it to be
detected and used correctly. Additionally a suitable ADF-item for our MCA system
needs to be copied to the reference disk to correctly register it with the system
- finished. All SCSI IDs except for ID 7 are available for the scanner - as it is
operated at this interface exclusively - that have to selected with the suitable
switch. Furthermore, the scanner needs to be terminated, in this case a passive
terminator is highly enough. After these preparations we have ensured that the scanner
operates independent from the other devices in the machine and does not slow them
down.
Generally you should ensure that only high-quality connectors and cables are
used for external devices that are connected to a SCSI machine, so distortion and
interference are avoided. This is true even more for the later SCSI standards whose
high transfer rates can only be achieved with first-class cables. The quality of
the round cables that are used for external devices can be determined from the codes
printed on them. On high-quality cables you can find - besides other data - the
characters "AWG" (meaning "American Wire Gauge"), followed by
two digits. The higher the given number, the better the cable's isolation and hence
the quality is. Usually cables of the norm AWG 28 are sufficient for SCSI-2 connections
while the norm AWG 30 can be viewed as the standard for SCSI-3 and Ultra/Wide SCSI.
As a comparison: High-quality printer cables usually comply to the norm AWG 26.
In part three of the workshop we are going to continue with practical configuration
of some models with PCI and ISA bus.
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