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Guest
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 Posted: Fri Feb 09, 2007 11:59 pm Post subject: Use of a differential external SCSI port with single ended d |
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Hello all...
I am no SCSI expert by any means, but I've learned a lot by running
SCSI devices on IBM PS/2 and Microchannel hardware.
However, all of this acquired knowledge is for single-ended devices
only. The few differential drives I have are of the LVD type, and all
are running in SE mode attached to SE controllers.
I recently came into a nice IBM Differential Fast/Wide controller for
one of my systems. I'd like to use it because I know at least the
drives internal to my system could go faster than the currently
installed controller will let them. My hope would be that using this
controller would let me take advantage of this potential. I don't
think the internal devices will be a problem, as I have it on good
authority that the internal bus of this adapter is single ended only.
This adapter is the 4-C model from an RS/6000 system, but it could
work on my x86 PS/2 Server 95.
The problem is that I have external devices which are single-ended in
nature. The external port on this adapter is clearly marked as being
differential (probably high voltage differential) in nature.
I'm afraid to connect any external single ended device to this port
because I can't be sure that doing so is safe for the adapter or my
devices. From what research I've done, I cannot find a definitive
answer on the subject. Some resources say it is possible, others say
to act with caution and the SCSI FAQ says "no". Leaving my external
devices attached to another compatible controller would be fine, if
that is the safest guaranteed option.
Can anyone here offer some advice on this subject? I would very much
appreciate whatever guidance can be offered.
William |
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Michael Baeuerle
Guest
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| Posted: Sun Feb 18, 2007 6:23 pm Post subject: Re: Use of a differential external SCSI port with single end |
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wm_walsh@hotmail.com wrote:
| Quote: |
I recently came into a nice IBM Differential Fast/Wide controller for
one of my systems. I'd like to use it because I know at least the
drives internal to my system could go faster than the currently
installed controller will let them. My hope would be that using this
controller would let me take advantage of this potential. I don't
think the internal devices will be a problem, as I have it on good
authority that the internal bus of this adapter is single ended only.
This adapter is the 4-C model from an RS/6000 system, but it could
work on my x86 PS/2 Server 95.
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You mean the one listed here:
http://www.ibmmuseum.com/ohlandl/IBM_SCSI/SCSI-DFW.html
as FRU 52G3380?
The internal port of this card is listed as SE, the external as
"differential".
| Quote: | The problem is that I have external devices which are single-ended in
nature. The external port on this adapter is clearly marked as being
differential (probably high voltage differential) in nature.
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Yes, likely to be HVD.
Search for an icon like this near the connector:
http://scsifaq.paralan.com/pix1/scsisymbolHVD.gif
http://scsifaq.paralan.com/pix1/scsisymbolLVDMSE.gif
| Quote: | I'm afraid to connect any external single ended device to this port
because I can't be sure that doing so is safe for the adapter or my
devices. From what research I've done, I cannot find a definitive
answer on the subject. Some resources say it is possible, others say
to act with caution and the SCSI FAQ says "no".
|
In theory nothing should be damaged because the HVD hostadapter should
disable its transmitters after seeing the DIFFSENS line pulled to ground
(every SE device will do that). But nobody guarantees you that IBM have
implemented things correctly.
| Quote: | Leaving my external
devices attached to another compatible controller would be fine, if
that is the safest guaranteed option.
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Do that. HVD is not multimode capable like LVD, so it cannot work with
SE devices.
Micha
--
Mails containing HTML or binary Windows code are rejected. |
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Folkert Rienstra
Guest
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| Posted: Mon Feb 19, 2007 2:58 am Post subject: Re: Use of a differential external SCSI port with single end |
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"Michael Baeuerle" <michael.baeuerle@gmx.net> wrote in message news:q4tla4-je1.ln1@micha.freeshell.org
| Quote: | wm_walsh@hotmail.com wrote:
I recently came into a nice IBM Differential Fast/Wide controller
for one of my systems. I'd like to use it
because I know at least the drives internal to my system could
go faster than the currently installed controller will let them.
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Based on what?
| Quote: | My hope would be that using this
controller would let me take advantage of this potential. I don't
think the internal devices will be a problem, as I have it on good
authority that the internal bus of this adapter is single ended only.
This adapter is the 4-C model from an RS/6000 system,
but it could work on my x86 PS/2 Server 95.
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That's another big assumption.
| Quote: |
You mean the one listed here:
http://www.ibmmuseum.com/ohlandl/IBM_SCSI/SCSI-DFW.html
as FRU 52G3380?
The internal port of this card is listed as SE, the external as "differential".
The problem is that I have external devices which are single-ended in
nature. The external port on this adapter is clearly marked as being
differential (probably high voltage differential) in nature.
Yes, likely to be HVD.
Search for an icon like this near the connector:
http://scsifaq.paralan.com/pix1/scsisymbolHVD.gif
http://scsifaq.paralan.com/pix1/scsisymbolLVDMSE.gif
I'm afraid to connect any external single ended device to this port
because I can't be sure that doing so is safe for the adapter or my
devices. From what research I've done, I cannot find a definitive
answer on the subject. Some resources say it is possible, others say
to act with caution and the SCSI FAQ says "no".
In theory nothing should be damaged because the HVD hostadapter should
disable its transmitters after seeing the DIFFSENS line pulled to ground
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That is: when you power it up when cables are already connected.
When already powered up and connecting cables you are subject to chance.
| Quote: | (every SE device will do that).
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*Should* do that.
| Quote: | But nobody guarantees you that IBM have implemented things correctly.
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Nor that "every SE device will do that".
There is also the cable that needs to have this line connected.
| Quote: |
Leaving my external devices attached to another compatible
controller would be fine, if that is the safest guaranteed option.
Do that. HVD is not multimode capable like LVD,
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It's not even pin compatible.
| Quote: | so it cannot work with SE devices.
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Because they didn't bother.
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Guest
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| Posted: Thu Feb 22, 2007 11:58 pm Post subject: Re: Use of a differential external SCSI port with single end |
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Hi!
| Quote: | because I know at least the drives internal to
my system could go faster than the currently
installed controller will let them.
Based on what?
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The spec sheets for the drives in question.
Also, some knowledge of the SCSI controllers at hand comes into play.
These SCSI controllers are busmaster capable, and the higher end
models have faster onboard CPUs driving the adapter. (Granted, the
improvement is not even across the board. There exists an early
narrrow cacheless version of this adapter built around an 8032/8052
micrcontroller that is notably faster than a cached version using an
80188.)
And finally--benchmarks from a 10,000 RPM Seagate LVD/SE drive
attached to this card. With the old controller, 10 megabyte/second
transfer was the best possible rate. With this new controller, 13.9
megabyte/second transfer is shown.
| Quote: | That's another big assumption.
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No, because it has been done by others, with an adapter that is the
*same* apart from the CPU onboard. Some FRUs of the adapter with the
slower CPU don't work, but nothing is harmed by this.
| Quote: | It's not even pin compatible.
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I will use a conventional adapter for my external devices. Already I
have covered the differential port so it will not be used by mistake.
William |
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Guest
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| Posted: Fri Feb 23, 2007 12:02 am Post subject: Re: Use of a differential external SCSI port with single end |
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Hi!
Yes, that is the one, although I think mine may have a different FRU.
The components are the same between the picture and what I have.
| Quote: | Search for an icon like this near the connector:
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I did not find an icon, there is only a label that says "differential"
near the port.
| Quote: | Do that. HVD is not multimode capable like LVD, so
it cannot work with SE devices.
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I have done that. The system has plenty of slots and using another
host adapter will not be a problem. I also covered up the differential
port so it cannot be used.
Thank you for the information.
William |
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