#Multi SCSI controllers
27 messages in this thread
Chris,
thanks a lot. Would you think that instead of <moving cabling back and
forth> between one and the other computer some kind of a data switch could
be used? Or would the SCSI transfer rates not permit manual switching? Any
idea?
I just recognize that I talk about a different subject, so I will try to
change the subject title.
Manfred <- flying from FRA via Autopilot (Amiga) 1.052
Manfred,
The high speed transfer rates of most scsi controllers would probably
not take kindly to switchboxes. Scsi controllers transfer data at speeds high
enough to generate standing waves on the cables, which is one of the reasons
for the need for terminators. When you start mixing cabling, connectors,
switches, etc., you are creating a potential for problems created by both the
standing waves and possible "crosstalk" between signal lines inside the
switchbox. The result might very well be an unreliable scsi chain. Obviously
there are solutions to these problems, but their costs may well outweigh the
benefits.
Thank you, Steven,
what I really am looking for is a possibility to have one SCSI controller
in the Amiga2000 and the other in the A2386SX bridgeboard, then externally
having Syquestr drives, CD-Roms, and maybe streamer I could work from both
processors with each device. Of course, the media have to be compatible
with the controlling software on the processor from which they are used.
It should be possible to have one SCSI bus with more than one controller,
shouldn't it?
Manfred <- flying from FRA via Autopilot (Amiga) 1.052
Manfred,
Well, you certainly can have a scsi controller on the PC side as well
as on the Amiga side in the same box. However, you can transfer files from the
Amiga side to the PC side without having to move the drive by using AREAD and
AWRITE which are part of the Janus software. Of course, if you need to take
the cartridge to a separate PC, that's a different problem and you would need
to be able to move the drive from one machine to the other. Before I installed
the multi-i/o card in my old 2000 I used a cheap Seagate ST02 scsi controller
on the PC side with a separate scsi drive while running the 2000 off a Nexus
scsi controller.
What you cannot do is use an Amiga controller to run a scsi drive on
the PC side except through the psuedo-drive. You can, however, partition a
hard drive on the PC side running from a PC controller with an Amiga and PC
partition. The Amiga partition would be used by the Amiga while the PC
partition is used by the bridgeboard. You cannot transfer files between them
except by using AREAD and AWRITE or by using CrossDos.
Steven,
yes I know about AREAD and AWRITE, and use them quite often. The idea here
is, that a CD-ROM drive could be used by both systems. The Amiga system
could read everything like .doc files etc. on a PC CD disk. But to run
(IBM/MSDOS/Windows)-programs directly off a CD disk, it would be necessary
to have direct access to the drive from the Bridgeboard.
If you don't have that you would have to AREAD the program and all
supporting files from the CD to some file in a bridgeboard drive, then
load and run it from there.
So you could use one external CD drive for running Amiga programs from
Amiga CDs directly in the Amiga (like Fish disk programs) and MSDOS
programs from MSDOS CDs directly using the Bridgeboard without
transferring anything.
The same would be true for using Syquest drives, though in this case JLINK
files could be used to achieve the same, except that you cannot exchange
data via the Syquest medium with other PCs, unless they are directly and
exclusively written by the bridgeboard. (Similar is the case for backup
tapes).
In your old 2000 the two SCSI controllers did probably not share the same
external devices, right? And I did not quite understand what you meant by
<<an Amiga controller (cannot) run an scsi device on the PC side _except
through the pseudo-drive_>>. Did you mean JLINK files?
Thank you.
Manfred <- flying from FRA via Autopilot (Amiga) 1.052
Manfred,
You cannot "share" the same drives on two different controllers. What
you can do is to move the drive from one controller to the other, assuming that
both the Amiga drive and the PC drive shared the same formats, which they
don't. However, CD ROMs could be read on either side assuming the Amiga had a
CD ROM filesystem that could read CDs formatted on a PC filesystem. However,
Fish disks could only provide you with a diskette formatted to be read on the
Amiga, not on the PC.
The best you could hope to do is to have a drive which could be moved
from the Amiga controller to the PC controller. Whether you could actually
read CDs on both sides would depend on the filesystem used to create the CD.
There are Amiga CD filesystems which will read PC CDs, but I don't think any
PCs could read CDs formatted only for the Amiga. Still, you could only move
the drive itself from one controller to the other, but you couldn't truly
"share" the drive – that is access it both from the PC and Amiga at the same
time.
As for the last comment, what I meant was that the PC cannot access a
scsi device connected to the Amiga. The only way the bridgeboard can provide
access to an Amiga scsi device is through the psuedo-drive or through JLINKed
virtual drives (except through AREAD and AWRITE.)
Manfred
Actually, I thought it was possible to create a scsi network connecting
two computers to a scsi chain allowing both to access a single device.
Obviously the controllers would have to have different adresses, and only
one could write to the drive at a time, but a CD-ROM would be a natural
since both systems could only read from it.
You might try Dave Cinege, I recall him mentioning that he set up
systems like this, going from an scsi on the amiga side to an scsi on the
bridgeboard side.
// .Cruising on AutoPilot
\X/
Yes and did it with a harddrive, and crossdos…wow what a technical
nightmare…but it works.
CD-ROMs would work easlity, since you don't have to worry about updating
the filing system, and such, since they are read-only
Dave
Elite MicroComputers – Flying high on AutoPilot
Mark,
I suppose you actually could do that, although what Manfred wanted to
do was to transfer files from one device to another while connected on both
sides. I think setting up a "sneaker" net might be more than he would
anticipate having to do.
Your wrong about this one Steven, (jeez I really am still needed here :>)
If he is dealing with SCSI controllers, then all you have to do is follow
the basic rules of ID's and termination, and 2 controllers can share the
devices. A CD-ROM set-up like this would work great…
Dave
Elite MicroComputers – Flying high on AutoPilot
Dave,
He wants to have the same device on an Amiga controller and on a PC
controller and access the same drive from both controllers. I don't think you
can have the drive simultaneously connected to two controllers at the same time
on two different busses, can you?
Depending on the two host adapters (what you called controllers), it is
certainly possible to hook them up to the same bus (the two different buses
become one bus when you connect them together). There are a number of possible
pitfalls…
1. The two host adapters must have different addresses, and must either (a) be
capable of operations with two host adapters, menaing that they must have the
ability to arbitrate for the bus, or (b) lacking that capability, they must be
manually prevented from operating at the same time.
2. If data on a drive is changed by one machine, the other machine will have no
way of knowing that it has been changed, which in turn means that any
information about the drive that is cached, will have to be discarded and
re-obtained. As you can imagine, writing to a drive that has been
surreptitiously changed would be a disaster.
I don't know about the clone side, but on the Amiga side, a LOT of information
about the drive is cached.
-larry
Larry,
With respect to the host adaptor on the Amiga, I have a 3000T, but I
don't know if the scsi circuitry can arbitrate, although I suspect it can.
However, on the PC side, if I understand you, I really would need a bus
mastering adaptor, is that correct?
This all stems from the possibility of accessing the scsi tape drive I
use on the Amiga from the PC, so I really don't much care about accessing any
of the Amiga hard drives.
Steven:
I think you're right about the bus mastering stuff, as the controller
(adapter) I use in the PC is the Adaptec 1542B, and it IS a bus mastering
device. Oh, and one other thing, I just remembered that the machines (both
of them) don't like being powered up at the same time, I have to powerup
the PC, then the Amiga (It's really simple, turnon PC, wait 1 minute, then
turn on Amiga). As I don't usually turn off any of my systems, this hasn't
been a problem for me.
// -Mike Schiller
\X/ AMIGA! On AutoPilot in sunny Fort Lauderdale
The 3000 SCSI host adapter will arbitrate just fine, as far as I know. On the
PC side (the other PC, that is, my PC is an Amiga), I have no idea. I don't and
won't have one in the house.
If you stick with accessing the tape drive from the clone, it should work just
fine.
-larry
Yes…
Elite MicroComputers – Flying high on AutoPilot
Yes, what? If I need a different scsi adaptor, what should I get?
Typing all the specifics out will make my fingers fall-off. Call me
voice…
Dave
Elite MicroComputers – Flying high on AutoPilot
Dave,
Well, Mike Schiller confirmed what you said about the scsi connections.
I really didn't think that you could actually chain across system busses. Now,
my interest is piqued. My tower has room for my spare VGA card and my ST02
SCSI controller for the PC. If I remove the multi-i/o card I can run a scsi
hard drive on the PC side and chain to the Amiga side and have access to my
tape drive for backup on the PC side. Unfortunately, my cheapo PC scsi won't
live with the IDE controller and it is very simple and cannot be flexibly
configured. The controller is "hard wired" at ID7. I don't even know if the
card is in any way terminated. It has no terminators on it and I never used it
but with one terminated drive when it was connected to the bridgeboard.
However, the card will handle up to seven devices, although I think the devices
must have their IDs in numeric sequence or it won't recognize a device.
Can I just daisy chain this sucker anywhere on the Amiga scsi chain,
renumber the Amiga controller to ID6, and it would, presumably, "see" the Amiga
devices already on the chain? The controller also has no drivers or software.
I don't even know if it will work with a scsi tape drive through Fastback
unless there is a driver. Does this mean I really need a "better" controller,
perhaps with the Corel suite of drivers? If I really need a better scsi
controller for the PC side, which would be the best device to look at? Of
possible concern would be one that is known to work with OS/2 2.1 (I have it,
but don't know if I ever want to use it.)
Sounds about right….
Elite MicroComputers – Flying high on AutoPilot
Steven:
I've had good luck with my Adaptec 1542B SCSI adapter (controller),
although they're no longer made, and I don't know if their 1542C will work
as well or not. It might. The main difference between the 1542B & C is
that the B is all set jumpers on the board, whereas the C is all setup in
software, so who knows it might even be better!
// -Mike Schiller
\X/ AMIGA! On AutoPilot in sunny Fort Lauderdale
Steven:
You can't share drives on 2 different controllers? Gee, I better not tell
that to my Amiga or the 486 next to it, as they both share the same SCSI
bus between the 2 machines! I have the PC controller set to ID5, and the
Amiga's controller to ID7, and all the other ID's are filled except ID1
which is still open. I currently have my fixed HDs for use only by the
Amiga, but my CDROM drive, TAPE drive, and SyQuest drive are all usable by
either machine. I'm running SVR3.2 Interactive Unix on the 486, and
somebody wrote an Amiga filesystem for Linux (A Unix Clone), and if I can
get that up and running on real Unix, I'll at least have read only access
to my Amiga HD's from the PC as well. As a test, I've even had both the
Amiga, and the PC cd'ed to the same directory on the CDROM, and typed in
an 'ls' on both machines, and hit both return keys at the same time, and
had no problems, both directory listings appeared almost at the same time.
I don't know if they both actually read the CDROM, or if they both just
read the same flow of data from the CDROM, or what, but there wasn't any
slowdown because they were both accessing the drive at the same time. Of
course, if the drive was a read/write drive I don't think I'd want to do
this, but in a read only situation, I see no problems.
// -Mike Schiller
\X/ AMIGA! On AutoPilot in sunny Fort Lauderdale
Mike,
Well, Dave Cinege said the same thing, so I guess I sure missed this
one. If you're doing it, then you are doing exactly what Manfred wants to do.
I really didn't think you could do that across the two different busses.
Perhaps you should pass along what you're doing to Manfred, because that's what
he wants to do.
Mike,
thanx a lot for your info. That is exactly what I wanted to do – with
the difference, that my PC is not a stand-alone, but a A2386SX card of C=
– and I am not running UNIX.
I have at the moment GVP SCSI controller on the AMIGA, harddisk, SyQuest
drive, and CDROM drive, and I wondered installing an SCSI controller on
the PC side with a harddisk instead of the now installed ATBus harddisk.
That would use 6 IDs, 2 for the controllers plus 4 for the devices.
It appears from your configuration that the controllers need not
necessarily have the highest or the lowest IDs, right?
When I read your comment one probably could build some kind of a network
just with the SCSI chain, including a third PC (this time stand-alone),
wouldn't you think that?
Manfred <- flying from FRA via Autopilot (Amiga) 1.052
> one probably could build some kind of a network just with the SCSI chain,
Well, yes and no. Again, the problem is that when one computer writes to a
disk, the other one (or other ones) has no knowledge of it, and cannot properly
use that disk until it reaquires the information. This can be done with a
'diskchange' command, but it is by no means automatic.
If you are thinking of using each computer directly, by transferring
information directly between the host adapters, it is possible under the SCSI
specification, but the host adapter has to support being the 'slave'. Most, if
not all, Amiga host adapters do not support this mode.
-larry
Manfred:
Well, it depends upon what you call a network. If you have a LARGE hd that
you want all three machines to share, yes, that is doable. If you want to
be able to share printers, etc, that might not be as doable.
As far as the SCSI setup itself, you need to have a harddrive as ID0, as
on PCs (they're more limited than Amigas) they expect the machine to have
harddrives only at ID 0 or 1. The HD at 0 would best be dedicated to the
PC, while other drives could be used for the Amiga. With the GVP
controller, you might HAVE to leave it at ID7, then you could set the PC
controller at ID6, and have the Amiga HD at 5 or so. I have my SyQuest as
ID 0, and maybe you should do the same, that way you can have cartridges
formatted as PC cartridges, or Amiga cartridges.
Using this sort of setup, it might even be possible (if you're willing to
experiment) to have a PC cartridge that would have the standard MS-DOS
boot block (I forget what they call it), as well as an Amiga RDB setup
with CrossDOS so you could access the disk from either machine.
BTW, when I refer to the MSDOS machine, I AM refering to the BB within
your Amiga. Being that you'll have to use an actual PC SCSI card for all
purposes it's the same thing as having a totally seperate PC, rather than
a BB inside the Amiga.
// -Mike Schiller
\X/ AMIGA! On AutoPilot in sunny Fort Lauderdale
Mike:
Thank you for all your info to this subject. All this discussion gave me a
lot of new ideas to solve the problem.
To read CD-ROM from both processors (I am of course talking about an Amiga
2000 and a A2386SX bridgeboard PC) my conclusion is: I do _not_ need the
"multi SCSI" connection: I can read any files from the CD just using
(from the PC) the aread command.
(Example: If the CD-ROM on the Amiga has the (software) device name of
"CD0:" then I just can read the files of a directory on the CD to the PC
directory "C:\temp" by writing:)
aread CD0:dir/#? c:\temp /B
This works beautifully. This is how I can read on the PC an Amiga-CD or a
Windows-CD or a DOS-CD – it does not make any difference!
The SCSI connection would give two more opportunities: To "dir"
directories (list files) and to execute programs directly from the CD
without transferring them first to the PC drives. Since quite a number of
those files on the CD is compressed I would have to do that anyway – so I
don't loose too much. The directory listings for the CDs I keep on my
SyQuest (on the Amiga-SCSI) as text files, and read them from there, again
using "aread".
Manfred <- flying from FRA via Autopilot (Amiga) 1.052