[Simh] TE16 CRC Errors

[Larry Baker]

Peter,

I answered my own question.  The VAX/VMS Version 1.6 SPD (http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/AE-C770D-TE%20VAX-VMS%20Operating%20System,%20Version%201.6%20SPD%2025.1.4.pdf) specifically states Mixed-MASSBUS configurations were supported:


NOTE:

MASSBUS disk drives and magnetic tape transports can be attached to the same MASSBUS.


Your predicament remains a mystery.

Larry Baker
US Geological Survey
650-329-5608
baker at usgs.gov



> On 7 Nov 2017, at 3:57:13 PM, Larry Baker <baker at usgs.gov> wrote:
> 
> Peter,
> 
> My reading of your hardware setup sounds like what was called a "Mixed-MASSBUS" configuration, that is, mixing disks and tapes on the same MASSBUS.  PDP-11 RSX-11M-Plus supported Mixed-MASSBUS.  We dual-ported all our disks and used the MASSBUS that came with our tape drives that way.  I think Mixed-MASSBUS support was unusual.  I do not remember if VMS 3.0 supported Mixed-MASSBUS.  If not, what you are seeing might be the result.
> 
> Larry Baker
> US Geological Survey
> 650-329-5608
> baker at usgs.gov <mailto:baker at usgs.gov>
> 
> 
> 
>> On 7 Nov 2017, at 12:54:40 PM, simh-request at trailing-edge.com <mailto:simh-request at trailing-edge.com> wrote:
>> 
>> ------------------------------
>> 
>> Message: 4
>> Date: Tue, 7 Nov 2017 20:54:31 +0000
>> From: Peter Allan <petermallan at gmail.com <mailto:petermallan at gmail.com>>
>> To: "simh at trailing-edge.com <mailto:simh at trailing-edge.com>" <simh at trailing-edge.com <mailto:simh at trailing-edge.com>>
>> Subject: Re: [Simh] Simh Digest, Vol 166, Issue 12
>> Message-ID:
>> 	<CAJCrz55fv2uBE5PhmtboUXL5Yzt8CpyiYhn1CyGxgHZHbXEkyw at mail.gmail.com <mailto:CAJCrz55fv2uBE5PhmtboUXL5Yzt8CpyiYhn1CyGxgHZHbXEkyw at mail.gmail.com>>
>> Content-Type: text/plain; charset="utf-8"
>> 
>> In order to try to understand why I am having trouble reading a simulated
>> tape with a simulated TE16 tape drive on a simh VAX 780, I have tried
>> several configurations.
>> 
>> 
>> Firstly, a point of clarification. The problem that I came across was in
>> finishing the installation of VMS 3.0. This was necessary in order to be
>> able to install VMS 1.5 using DSC2, but I have no problem with the
>> installation of VMS 1.5 itself. VMS 1.5 is a red herring - the problem is
>> with VMS 3.0.
>> 
>> 
>> I had configured a VAX 780 in simh with three RP06 disk drives and two TE16
>> tape drives. I was using TE16 tape drives rather than TS11 really just
>> because when I was the system manager of a real 780, it had two TE16 tape
>> drives.
>> 
>> 
>> All of this has been done on a host system running CentOS 5 (for simh
>> 3.8-1) and CentOS 6 (for simh 4.0).
>> 
>> 
>> To remind you of the problem, I started the installation of VMS 3.0 by
>> booting stand-alone backup and restoring a saveset from a tape that I
>> downloaded from the University of Stuttgart. The first phase went fine and
>> when I rebooted the 780, the system asked which device contained the
>> installation media so that it could automatically complete the installation
>> of VMS. I entered MTA0: and this is where things went wrong. Wilm suggested
>> I should trying using a TS11 drive (MSA0) rather than a TE16 drive and this
>> did indeed work, but this left me wondering why?
>> 
>> 
>> I have tried to restore a BACKUP saveset from a tape to a disk using
>> several configurations. I have tried:
>> 
>> -          Two difference versions of simh, 3.8-1 and 4.0
>> 
>> -          Three different versions of VMS, 3.0, 4.6 and 7.3
>> 
>> -          Different simulated tapes
>> 
>> -          The two different simulated tape drives, TS11 and TE16
>> 
>> The results have surprised me.
>> 
>> 1)      Changing the version of simh makes no difference to the results.
>> 
>> 2)      I only get a problem in restoring a saveset from tape when running
>> VMS 3.0 as the operating system. Everything works fine with VMS 4.6 and 7.3.
>> 
>> 3)      I have tried different tapes, but if the system is going to fail to
>> do a restore operation, it does it with all of the tapes containing BACKUP
>> savesets that I tried.
>> 
>> Following a suggestion from Kevin Handy, I tried to copy the savesets from
>> tape to disk, but the copy failed on the VMS 3.0 system when using a TE16
>> tape drive.
>> 
>> 
>> My experiments indicate that there is a problem with VMS 3.0 when using
>> TE16 tape drives. However, this seems so unlikely, not least because the
>> sequence of operations that I have gone through is what hundreds (thousands
>> probably) of system managers must have done to install VMS 3.0 on real
>> hardware, including my predecessor with “my own” 780.
>> 
>> 
>> This leaves me stumped, but at least I have narrowed the problem down and I
>> am able to do the installation of VMS 3.0 (which lets me do the
>> installation of 1.5) by using a TS11 drive.
>> 
>> 
>> The only thing I can think of is to wonder if the way that VMS handled TE16
>> (i.e. massbus) tape drives changed between VMS 3 and VMS 4 and that somehow
>> there is a bug in simh that only rears its head on the earlier version. I
>> confess this is a stab in the dark.
>> 
>> 
>> Anyone got a bright idea about this?
>> 
>> 
>> 
>> Cheers
>> 
>> 
>> Peter Allan
>> 
>> 
>> 
> 

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