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From: pdb@sei.cmu.edu (Patrick Barron)
Newsgroups: comp.bugs.4bsd,comp.unix.wizards
Subject: Re: Cant access disks on second UDA50
Message-ID: <1929@aw.sei.cmu.edu>
Date: Sat, 18-Jul-87 01:58:12 EDT
Article-I.D.: aw.1929
Posted: Sat Jul 18 01:58:12 1987
Date-Received: Sat, 18-Jul-87 19:02:58 EDT
References: <6683@dartvax.UUCP> <441@eplrx7.UUCP>
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Reply-To: pdb@sei.cmu.edu (Pat Barron)
Organization: Carnegie-Mellon University, SEI, Pgh, Pa
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Keywords: unibus uda50
Xref: mnetor comp.bugs.4bsd:455 comp.unix.wizards:3298

In article <441@eplrx7.UUCP> lad@eplrx7.UUCP (Lawrence Dziegielewski) writes:
>I have 2 uda's running on several MicroVaxes,  and they all run fine.  I

If you have a MicroVAX, then you *don't* have a UDA-50, which is a UNIBUS
device.  The controller used on the Q-Bus is the KDA-50.

>suspect that it's you config that may be wrong.  Each uda can support 4
>devices,  and you have to (or should) tell config about them.  So,  your
>config should look like this:
> [config deleted]
>In your configuration,  you're asking unix to find ra2 on uda1 drive 2.
>This is not logically possible.  uda0 supports ra0, 1 ,2 and 3,  and the
>next uda device will support ra4, 5, 6 and 7.  That is what works for me.
>Also,  logical drive ra4 must be at physical drive 0 on the 2nd uda(not 2).
>Now I'll admit I don't have this up on a 785,  but it does work for the 3
>MicarVaxes I run.  And I also use the secondary uda address of 0160334 in
>the MVaxes floating address space.  You may want to check on the uda
>secondary address on a 785,  but I don't know why it'd be different.

It doesn't matter what you call the ra* devices, as far as I know.  If you
really wanted to do something silly, you could put ra0, ra2, ra4, and ra6
on uda0, and ra1, ra3, ra5, and ra7 on uda1.  Also, if you *knew* you weren't
ever going to use more than (for instance) two drives on each controller,
you could put ra0 and ra1 on uda0, and ra2 and ra3 on uda1 (even though there
is no really good reason to actually do something like this, except for the
minimal savings in the size of the kernel).

As far as the problem at hand goes:  the reason I'd heard that you shouldn't
put more than one UDA-50 on a single UNIBUS is that is chews up a *lot* of
bus bandwidth.  The logical consequence of two UDA's should be degraded
performance, right?  I'd never heard of having the system hang because of it.

One last consideration:  do you actually have enough backplane power to
run two UDA-50's along with whatever else you have?  I know that marginal
power can hang systems up or crash them (the DEUNA used to do this all the
time).

--Pat.