[Simh] VAX Tape Emulation?

[Zane Healy]

> On Feb 19, 2018, at 10:42 PM, Mark Pizzolato <Mark at infocomm.com> wrote:
> 
> On Monday, February 19, 2018 at 9:55 PM, Zane Healy wrote:
>> I’d posted about this nearly a month ago, and have made some real progress
>> this weekend.
>> 
>> Configuration:
>> MONK
>> OpenVMS 8.3/Alpha
>> Compaq XP1000/667
>> 
>> RENNY
>> OpenVMS 7.3/VAX
>> SIMH MicroVAX3900
>> 
>> I’m backing MONK up over the Cluster to a “tape drive” on RENNY.
>> 
>> First, Ubuntu includes a package for SIMH V3.8-1.  If you’re just using disk and
>> network, it seems to be just fine.  If you want to write tapes, it seems fine.  If
>> you want to read tapes, upgrade, as it appears to crash OpenVMS V7.3, at least
>> when messing with “tapes" the size I’m creating.  Hopefully the crashing isn’t a
>> clustering issue, I still need to test that.  I downloaded the latest SIMH sources,
>> and built them today, and I appear to be able to read tapes without crashing.
>> At least it doesn’t crash when reading from the SIMH VAX, I still need to try
>> reading one over the cluster on my Alpha.
> [...]
>> One stupid question, I assume that SIMH emulates the network interface at
>> 10Mbit.  Is there any way to speed that up?  Granted, all my real VAXen are
>> limited to 10Mbit, but a faster link in SIMH would be nice.
> 
> The network interface is not artificially limited to 10Mbit.  Years ago, I 
> measured some 25Mbit on my desktop system.  I suggest that you run 
> with the latest code from https://github.com/simh/simh.  Simh v3.8-1
> was from a long time ago, and significant changes have been made since 
> then.

I grabbed the latest copy of the source from GitHub yesterday.  I ran another backup last night using the current SIMH, and it was the first to die before finishing, but there could have been other issues.  I’m trying again, as that was also my first attempt and running it with the /LIST option.

As noted, the latest SIMH was needed to successfully read the tape (I simply did a listing).

It’s hard to judge the speed accurately, due to tape Metadata, but I’m seeing the ‘virtual tape’ be created at about 510KB/sec.  That is faster than what I was previously seeing.  I wouldn’t be surprised if part of the bottleneck is the virtual tape drive.

Zane