[Simh] VAXcluster on SIMH - is it possible?

[Jeremy Begg]

Hello Tim,

>Thanks Villy and Martin. After reading some VMS docs, I was able to get two
>virtual VAXen clustered. I'm going to try to get my Alphastation in the cluster
>next time I'm home. From what I've read, it sounds like you can have different
>versions of VMS within a cluster. Are there any limitations? Could you (in
>theory) cluster a SIMH VAX running OpenVMS 7.3 and an Itanium running OpenVMS
>8.3?

Yes you can have different versions of VMS in a cluster, but there's a
difference between what works and what's supported by HP.  (Note that SIMH
is not an officially supported platform for VMS anyway.)

HP supports two-architecture VMSclusters (i.e. VAX+Alpha or Alpha+IA64 or
VAX+IA64), but not 3-architecture (i.e. VAX+Alpha+IA64).  However there's
nothing in the VMScluster code to block the formation of a three-
architecture cluster and plenty of sites *have* VAX+Alpha+IA64 clusters
running.

Given that V7.3 is the last release of OpenVMS VAX you can be pretty sure it
will cluster with any later version of OpenVMS on Alpha or IA64.  There are
a couple of things that might trip up a VAX application in this environment:

 - Alpha and Integrity systems can use either ODS-2 or ODS-5 formatted
   disks with full functionality.  VAXes can mount an ODS-5 disk but will
   have trouble accessing a file which has a name that is not compatible
   with ODS-2 (and this includes directories with such names).

 - VAX limits the lock value block to 16 bytes but Alpha and Integrity allow
   64 bytes.  So an application which uses distributed locking to share
   information or control access to information, and relies on 64-byte LVBs,
   might run into problems with an older version of that application running
   on the VAX.

Regards,

        Jeremy Begg

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