[Simh] Questions on SIMH VAX

[Zane H. Healy]

On Wed, 9 Jun 2010, Marc Chametzky wrote:

> I can give some input from my experience on a few of these things...

Thank you, it tends to indicate what I am considering is doable.

>> Does anyone happen to know what kind of performance this would give?
>> How many VUPS would such a setup offer?
>
> I don't know how it would perform on your system as I'm not familiar with the 
> performance characteristics of the Atom processor. On my SIMH setup, which is 
> a virtualized Linux system running on an ESXi host using an AMD Phenom II X3 
> 710 processor (limited to 2 GHz on a single processor), I get 13 VUPs (using 
> SRI's PT_VAX.EXE).

I've no idea what that CPU is, as I'm not familiar with AMD products, but a
quick google would seem to indicate that's more than 3x the CPU power.  Of
course the Atom isn't designed for this sort of workload.  Even if it isn't
practical to run WASD, I could still do pretty much everything else on SIMH.

> I will note that I got better idle handling once I started running DECnet. I 
> think that SIMH dealt better when there was some occasional activity (such as 
> handling network packets) rather than a truly idle system.

It would definitely be running DECnet Phase IV, as I'd want to be able to
talk to my PDP-11's, and have it on HECnet.

>> I assume that Volume Shadowing is supported, so that I can place disk 
>> images
>> on seperate physical hard drives and turn on shadowing?
>
> That should work just fine. There might be an issue with SIMH working 
> properly if one of its virtual drive volumes becoming unavailable, though, so 
> an advantage of volume shadowing (system reliability) probably goes away.

My thought was to have redundancy should I loose a physical HD.  Which is
why I use Volume Shadowing on my Alpha.

>>  What about
>> clustering with real physical VMS systems if I desire it?
>
> I've done it in the past using SIMH VAX clustered with a hardware Alpha box. 
> It worked just fine.

Perfect, as if I were to use it, I'd want to be able to cluster with a
MicroVAX III and an Alpha at a minimum.

>> How large of
>> virtual disks does SIMH support?
>
> Big. :-) Using a command like "set rqb0 rauser=N" in vax.ini, I'm able to use 
> large drives including one that's 15 GB. I did need to tweak my sources in 
> order to get large volumes working properly at some point in the past (an 
> issue with the large file APIs), but that was some time ago and I don't 
> recall whether it was still needed with the current sources.

My Alpha currently runs with 3 36GB drives, and 1 50GB drive.  Though I
could trim down the required space.

Zane