Date: Thu, 24 Dec 1992 08:25:47 EST
From: Richard E. Lynch <RICH@wvnvm.wvnet.edu>
Newsgroups: bit.listserv.ibm-main
Subject: Re: Logical Partitions/Physical Partitions

In article <IBM-MAIN%92122314530248@RICEVM1.RICE.EDU>, Michael Stein
<CSYSMAS@UCLAMVS.BITNET> says:
>
> - reliability
>   VM adds yet another point of failure to your MVS system.  Also
>   in my experience VM isn't as good at recovering from errors as
>   MVS -- thus it's not just another point of failure, it's worse
>   than just twice as bad as MVS alone.

The reliability of VM is much improved since VM/XA. We have been running
VM/XA or VM/ESA for years and have had only a couple of failures. MVS
has had a few failures too. There is also the guest recovery support
where VM can fail with minimal impact on preferred guests. We go for
months without a single VM IPL. For us, VM reliability has been about
the same as MVS reliability. I feel that these days, the reliability of
VM is not a big issue. I can not say the same for pre-XA releases of VM.

>
> - support of new hardware
>   VM tends to have later support for new hardware, thus
>   restricting you from installing new hardware (and selling the
>   old while it's still worth something).

Agreed. Support for new devices in VM does tents to come after the
support has already been added to MVS.  However, this has never been
a problem for us and I doubt it's much a problem for anyone else. The
support for new devices comes soon enough. Also, dedicating these
devices to the guest is a reasonable option when native support in
VM is lacking. Once again, this has never been a issue for us.

>
> - complexity
>   VM is much more complex than LPAR.  Besides taking system
>   programmer time to support/maintain it, there are more things
>   which can go wrong (I/O support, CMS which is at least needed
>   to maintain VM).

Depending on what you intend to do with VM, systems support may not be
all that significant.  If you provide CMS access to your users then
of course there is some significant systems support issues.  However,
that support would be required regardless of LPAR or NOLPAR.  If you are
simply using VM to run guest operating systems then the support requirements
are minimal.  Follow the "cook book" to install it and leave it alone.

>
> - performance (?)
>   It's easy to say that VM and LPAR should have the same
>   overhead, however it may not be.  It's probably easy to start
>   using some VM services which have a large impact on the
>   performance.  And if you can't use the VM services why pay for
>   VM?  (reliability, $, maintenance, support etc).

I don't buy this.  A V=R guest under VM performs approx. the same
as a LPAR guest.  If you start using "some VM services" then it's
because you need them and I don't see how that could significantly
impact an isolated V=R guest.

Running guests under VM has many advantages and is more flexible. The sharing
and reconfiguration of devices; Reduced hardware requirements; Use of virtual
CTCA's instead of real ones.


Richard E. Lynch
West Virginia Network for Educational Telecomputing (WVNET)
Manager of IBM Systems Programming
837 Chestnut Ridge Road
Morgantown, WV  26505          Bitnet:   RICH@WVNVM.BITNET
Tel: (304) 293-5192            Internet: rich@wvnvm.wvnet.edu
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