[SunRescue] Proper use of VME scsi controllers?????

[Greg A. Woods]

[ On Tuesday, February 8, 2000 at 11:56:21 (-0500), BSD Bob wrote: ]
> Subject: [SunRescue] Proper use of VME scsi controllers?????
>
> I was browsing my pile of ancient sun scrolls, and ran across some
> early 3/4xx install/config manuals that stated to the effect that
> a sun2 controller should only be used on servers with it only running
> the 1/4 inch tape.  I thought that a bit perplexing, since I have run
> my 3/xxx and 4/xxx boxes with sun2 controllers hacked with external and
> internal bus lines, and they seem to work fine, as long as only one
> pair of devices is hung externally, plus the internal tape.  The scrolls
> suggest that such shennanigans are technically ``unsupported''.  It also
> works fine on sun3 controllers.  So, my questions are:

The sun2 controller is Multibus controller (thus requiring one of the
many Multibus-VME adapters) that is extremely brain-dead, somewhat
slower than the sun3 controller, and probably not 100% SCSI compliant.
It does work well enough for the 1/4" MT02 (SCSI->QIC36) interface and
it makes a lot of sense to put tape drives on a separate bus from the
disks they are likely to be used to backup, especially on older and
slower SCSI subsystems.  Mixing disks and tape, especially on a sun2
controller, will cause serious performance degradation.

Sun has a long history of avoiding stupid user-support nightmares by
simply saying that odd-ball and un-tested configurations are "unsupported".

> 1.  What are the approved ways to run both internal and external devices
>     on the scsi bus on say a 12 slot deskside cabinet?  How many devices
>     and how should they be hung?

Anything's possible, within the realm of the SCSI bus physical specs.

> 2.  What are the approved ways to run two controllers, where one runs
>     the tape, like a sun2 controller, internally, and the other, like
>     a sun3 controller with external connector hacks runs the external
>     bus.  Or, maybe run the tape and a pair of internal drives on one
>     controller and external drives on the second controller.

Depends on what your other available peripheral hardware is, physically.

Ideally you would put the sun2 controller in slot-7 (i.e. with a
501-1149 adapter) and hook the tape drive up internally.  Then put an
external-only sun3 controller in another (supported) slot (that means
getting the right 6u-9u adapter, probably a 501-1217, that does *not*
connect to the backplane; and connect it to an external disk chassis of
some (any!) description.

> 3.  How does one get an internal tape and 4 external drives on one
>     sun3 controller?  I get maxed out at 2-3 drives and tape before I
>     start getting scsi bus busy errors.  ONE time I got 4 drives and
>     tape up, but it was not real happy.  There has gotta be a way
>     to keep the bus happy, and lots of devices hung thereon.

I never had that problem on my 3/260s.  I had the internal tape, an
internal drive, two external disk drives, an external CD-ROM, and an
external tape (i.e. all target units were occupied).

You do have to follow the SCSI physical specifications very closely
though.  I.e. you must not ever exceed the total cable length
limitations (3m).  Avoid as many connectors as possible (i.e. use a
large external chassis with a single internal ribbon cable).  Avoid
using stub cables on devices (even though the spec. allows some).

Ideally you'll want to provide termination power from one or more of the
drives in the external chassis and always be extremely careful to use a
high-quality active (or forced-perfect) terminator on both ends of the
bus.  So long as your external chassis power supply matches your
internal one in voltages the use of multiple termination power sources
on the SCSI bus should not harm anything.

I used the on-board (active) termination on the internal drive (a wee
quantum 3.5" drive) and a Sun-original active terminator externally on
my SCSI chassis.  I had only the one internal ribbon cable from the
backplane to the tape and disk, one external sun-original connector
cable with the EMI filters, plus the internal ribbon in the external
chassis.  This worked like a charm on my 3/260, and then on the 3/280 it
was transformed into, and finally on the SS2 I use today.

> 4.  What can the kernel stand in the way of multiple scsi controllers?
>     And, how should they be set up?  I sense two, but somewhere I thought
>     I saw in one fellow's hackers notes that it could handle 4, with
>     proper jumpering and setup.

Dunno.  I had trouble getting a sun2 and sun3 SCSI controller working
simultaneously on my 3/260 with SunOS-4.1.1u1.  I didn't fiddle too much
with the drivers though and I was mostly holding off until I could
upgrade to NetBSD and help with the effort to complete the sun2 (sc)
driver but of course that hasn't happened yet.  You might have better
luck with your 4/260 if there's still an 'sc' driver in the sparc
SunOS-4 version.

I've also as yet been unsuccessful at getting two sun3 (si) controllers
working under NetBSD, but then the last time I tried was a couple of
years ago and I didn't spend very much time on it either.

-- 
							Greg A. Woods

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