Re: simh emulator and cluster
From: Stanley F. Quayle (stan_at_stanq.com)
Date: 05/12/03
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Date: Mon, 12 May 2003 14:56:47 -0400
On 11 May 2003 at 22:12, David J. Dachtera wrote:
> Please approach this with great caution until you have made very certain
> that there is no danger to your production systems.
I concur. Once your SIMH machine enters the cluster, it must respond
promptly to all cluster messages. You might hack SYSGEN parameter
RECNXINTERVAL bigger on all cluster members, but that would make any
cluster transition longer.
One downside of how SIMH works is that it puts the Ethernet adapter
into promiscious mode. This means the adapter will "hear" absolutely
everything on the network, and the host system will have to process
each message. If that process "falls behind", you will have big
problems. The inevitable cluster failure might be the worst of your
problems. [Shameless commercial plug: CHARON-VAX doesn't do this.]
A work-around would be to install a second Ethernet adapter on your
system and configure SIMH to use that adapter. Make sure your host
doesn't start any other services on that adapter, and put it behind a
switch or router that filters all the non-SCS traffic. This is
easier said than done, however, since most switches and routers don't
know anything about SCS.
As for having the cluster members use the host's disk space, you will
have to serve a bunch of disk images from SIMH. Only those images
you share will be visible to the cluster members, and cannot be
combined into a single volume.
Might I suggest a better idea? I assume that you have TCP/IP
installed on these VMS systems.
Instead of emulating a VAX, why not use NFS to serve your host's
entire disk to the VMS systems? I do this myself, using a Linux
system to serve a 130 GB disk for my VMS cluster (both VAX and Alpha)
to use for backups, etc.
If you mount the disk correctly, using the /ADF=CREATE parameter, you
can have the VMS systems use the NFS share and they'll create hidden
files which preserve the VMS file characteristics. All you need to
do is to configure in the NFS client on the VMS systems, and you
should be good to go.
--Stan Quayle
Quayle Consulting Inc.
----------
Stanley F. Quayle, P.E. N8SQ +1 614-868-1363 Fax: +1 614 868-1671
8572 North Spring Ct. NW, Pickerington, OH 43147
Preferred address: stan@stanq.com http://www.stanq.com
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