scsi_config_and_termination

This is part of The Pile, a partial archive of some open source mailing lists and newsgroups.



Subject: [OT] Scsi Termintation
From: Ahbaid Gaffoor <ahbaidg@worldnet.att.net>
Date: Sun, 03 Sep 2000 13:28:10 -0700

Hi all,

I'm almost doen building my linux - oracle database server...

Just one question for the SCSI experts.

The board is a supermicro P6DBS with an onboard adaptec SCSI controller.

I have four seagate ST12550N 50 pin SCSI drives, and the board has a 50
pin interface. I also have a 50 pin SCSI cd-rom and a 50 pin cable that
can handle seven devices.

Here's the plan:

Let's say the cable is numbered from the motherboard connector to the
last device on it as 0 through 7.

I plan to put the cd-rom on 1, the four drives on 2 through 5, leaving 6
and 7 unattached.

Do I need to get a SCSI terminator? If so, do I put it on 6? Or, if the
drive on 5 can be made to terminate, is that what I should do?

Your advice is all welcome.

thanks,

===
Subject: Re: [OT] SCSI LVD Cables
From: John Aldrich <john@chattanooga.net>
Date: Sun, 3 Sep 2000 14:15:58 -0400

On Sat, 02 Sep 2000, Ahbaid Gaffoor wrote:
> Hi,
> 
> what does the LVD thing mean when talking about SCSI?
> 
> Is it something analagous to 66/Mbs IDE?
> 
> If so, is it's use supported under Linux?
> 
It depends entirely upon the controller and the hard drive
and has nothing to do with the operating system, AFAIK. If
your SCSI controller is supported under linux, I think that
LVD will work with linux.

LVD==Low Voltage Differential, AKA (I think) Differential
SCSI. Your hard drives MUST be LVD drives, your controller
has to be an LVD controller and I think you may also need
special cables. You will *definitely* need different
termination, if termination isn't built-in as an option on
your last LVD device.

===

Subject: Re: [OT] Scsi Termintation
From: Ahbaid Gaffoor <ahbaidg@worldnet.att.net>
Date: Sun, 03 Sep 2000 14:00:26 -0700

Any advatnges or disadvantages of setting the SCSI id's on the devices as they
progress along the cable?

That is, first device from controller - SCSI ID 0  (The cd-rom, first
connector)
Second device   - SCSI ID 1 ( the first drive, second connector)
Third Device - SCSIS ID 2 (the second drive, third connector)
etc.

Or can I just place them anywhere along the cable?

I tend to think that it is easier to keep track of things by placing them in
order...

regards and thanks,

your answer has cleared things up a lot.

===

Subject: Re: [OT] Scsi Termintation
From: John Aldrich <john@chattanooga.net>
Date: Sun, 3 Sep 2000 15:13:12 -0400

On Sun, 03 Sep 2000, Ahbaid Gaffoor wrote:
> Hi all,
> 
> I'm almost doen building my linux - oracle database server...
> 
> Just one question for the SCSI experts.
> 
> The board is a supermicro P6DBS with an onboard adaptec SCSI controller.
> 
> I have four seagate ST12550N 50 pin SCSI drives, and the board has a 50
> pin interface. I also have a 50 pin SCSI cd-rom and a 50 pin cable that
> can handle seven devices.
> 
> Here's the plan:
> 
> Let's say the cable is numbered from the motherboard connector to the
> last device on it as 0 through 7.
> 
> I plan to put the cd-rom on 1, the four drives on 2 through 5, leaving 6
> and 7 unattached.
> 
> Do I need to get a SCSI terminator? If so, do I put it on 6? Or, if the
> drive on 5 can be made to terminate, is that what I should do?
> 
Put the last device on position 7 and use the on-board
termination, if available. Otherwise, put it on 6 and use a
terminator.

===

Subject: Re: [OT] SCSI LVD Cables
From: wyrd <wyrd@triskelion-nova.com>
Date: Sun, 03 Sep 2000 12:33:47 -0700

Your hard drives MUST be LVD drives, your controller
> has to be an LVD controller and I think you may also need
> special cables.

That's not entirely true.  I had an LVD drive in use for
quite awhile on a non-LVD controller.  Some drives have
jumpers that allow them to be used in an existing system.
There are also adapters available.

							~Rob

===

Subject: Re: [OT] Scsi Termintation
From: "Mikkel L. Ellertson" <mikkel@Infinity-ltd.com>
Date: Sun, 3 Sep 2000 15:37:22 -0500 (CDT)

On Sun, 3 Sep 2000, Ahbaid Gaffoor wrote:

> Any advatnges or disadvantages of setting the SCSI id's on the devices as they
> progress along the cable?
> 
> That is, first device from controller - SCSI ID 0  (The cd-rom, first
> connector)
> Second device   - SCSI ID 1 ( the first drive, second connector)
> Third Device - SCSIS ID 2 (the second drive, third connector)
> etc.
> 
> Or can I just place them anywhere along the cable?
> 
> I tend to think that it is easier to keep track of things by placing them in
> order...
> 
> regards and thanks,
> 
> your answer has cleared things up a lot.
> 
> Ahbaid.
> 
Well, the device number actualy affects who gets the SCSI bus if more then
one device want it at the same time.  The higher the number wins.  You
would think because of this that you would want the hard drives to have
the highest numbers, but this is not the case.  Hard drives are usualy not
time critical when sending/recievign data - that is what they have buffers
for.  Tape drives tend to have tighter timing requirments.

Also, it is normal practice to make the hard drive you are going to boot
from ID 0.  (Some older hardware requires that you boot from ID 0.)
ALso, if you change SCSI IDs, you may change the mapping of your hard
drives under Linux.  Linux maps the first SCSI hard drive it finds to
/dev/sda, the second to /dev/sdb, and so on.  It does the same kind of
mapping for other SCSI devices.  So if your SCSI CD is device 0 now, and
you deside to add another hard drive later, and put it as ID 0 because you
are plugging it in where the CD drive was, it now becomes /dev/sda.  Now
your /etc/fstab is out of sync with your physical drives.  Lots of fun.

NOw, if you were using a older Sparc Station, you would want the CD as ID
6, and if you have a SCSI tape, you want that as ID 5.  This is because
the boot PROM on expects them there by default.  You can do things like
boot CDROM or boot TAPE with them.


===

Subject: Re: [OT] SCSI LVD Cables
From: John Aldrich <john@chattanooga.net>
Date: Sun, 3 Sep 2000 20:24:05 -0400

On Sun, 03 Sep 2000, wyrd wrote:
> > Your hard drives MUST be LVD drives, your controller
> > has to be an LVD controller and I think you may also need
> > special cables.
> 
> That's not entirely true.  I had an LVD drive in use for
> quite awhile on a non-LVD controller.  Some drives have
> jumpers that allow them to be used in an existing system.
> There are also adapters available.
> 
Thanks for setting me straight. I was under the impression
you had to have an LVD drive with an LVD controller. :-) My
SCSI knowledge is somewhat limited by what more
knowledgeable people have told me in the past. My
understanding was as I'd mentioned previously. :-)
	John

===

Subject: Re: [OT] SCSI LVD Cables
From: "M. Neidorff" <neidorff@bellatlantic.net>
Date: Sun, 03 Sep 2000 20:55:48 -0400

At 12:33 PM 09/03/2000 -0700, you wrote:

> > Your hard drives MUST be LVD drives, your controller
> > has to be an LVD controller and I think you may also need
> > special cables.
>
>That's not entirely true.  I had an LVD drive in use for
>quite awhile on a non-LVD controller.  Some drives have
>jumpers that allow them to be used in an existing system.
>There are also adapters available.

My experience, I've just added a LVD drive to an ultra scsi system.  The 
drive (seems to) have stepped down seamlessly to ultra scsi speed and work 
fine.  The drive is terminating itself (I didn't do a thing to make it 
terminate).

===

Subject: Re: [OT] Scsi Termintation
From: "M. Neidorff" <neidorff@bellatlantic.net>
Date: Sun, 03 Sep 2000 21:07:29 -0400

At 03:13 PM 09/03/2000 -0400, you wrote:
>On Sun, 03 Sep 2000, Ahbaid Gaffoor wrote:
> > Hi all,
> >
> > I'm almost doen building my linux - oracle database server...
> >
> > Just one question for the SCSI experts.
> >
> > The board is a supermicro P6DBS with an onboard adaptec SCSI controller.
> >
> > I have four seagate ST12550N 50 pin SCSI drives, and the board has a 50
> > pin interface. I also have a 50 pin SCSI cd-rom and a 50 pin cable that
> > can handle seven devices.
> >
> > Here's the plan:
> >
> > Let's say the cable is numbered from the motherboard connector to the
> > last device on it as 0 through 7.
> >
> > I plan to put the cd-rom on 1, the four drives on 2 through 5, leaving 6
> > and 7 unattached.
> >
> > Do I need to get a SCSI terminator? If so, do I put it on 6? Or, if the
> > drive on 5 can be made to terminate, is that what I should do?
> >
>Put the last device on position 7 and use the on-board
>termination, if available. Otherwise, put it on 6 and use a
>terminator.

There are 3 things to keep in mind: position, SCSI ID and termination.

First, position doesn't matter.  (we are dealing with signals near the 
speed of light here)

SCSI ID is important.  Each device must have a unique ID, in your case 0 - 
7.  It is settable through either jumpers or some other mechanism on the 
device itself.  The controller usually is ID #7 and its best to just let 
this be.  Beyond that, it doesn't matter what ID you give other devices.

Termination is very important.  You may be dealing with older scsi devices 
in which case they may or may not have built in termination.  If they do 
have the built in termination, it may or may not be good enough (isn't this 
wonderful!!!).  You  are going to have to check the pinouts and figure it 
out for each drive and device.  The ones at the physical ENDS of the scsi 
chain MUST, MUST, MUST be terminated.  If the controller is the end of the 
chain (you are just using the internal or external cable connection) then 
the controller must be terminated.  If you are using both the internal and 
external connections, then the controller must be un-terminated and the 
device at the end of the chain must be terminated.  Again, you are going to 
have to hit the docs of the controller to see what is what for the built in 
termination.

===



the rest of The Pile (a partial mailing list archive)

doom@kzsu.stanford.edu