Radoslaw Skorupka wrote:
>RLS require Parallel Sysplex, but not everyone need it.
We should be more precise and careful, to avoid any misunderstandings. VSAM
RLS requires:
* At least one z/OS instance (let's go with exactly one in this example);
* A Coupling Facility (CF)(*), which can even be on the same physical
machine.
And that's it! You do NOT *need* two z/OS LPARs to support VSAM RLS (and
Transactional VSAM). You need two basic ingredients: z/OS (one works) and a
Coupling Facility (one works). For Transactional VSAM you also need the
z/OS DFSMStvs software license.
This IBM redbook ("VSAM Demystified") illustrates VSAM RLS in a z/OS
Monoplex in Section 5.1.4:
http://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf
Possible formal definitions aside, most people interpret "Parallel Sysplex"
as including two or more z/OS instances, at least in normal operations. But
no, even during normal operations you only *need* one suitably configured
z/OS instance for VSAM RLS and Transactional VSAM, to be clear. There might
be other reasons to have more than one z/OS instance, but you don't need a
second z/OS instance to run these two highly useful VSAM technologies.
In this example, you, your colleagues, and management might decide,
perfectly sensibly and rationally, that a particular set of CICS
applications (let's suppose) and the services they provide are well suited
to a z/OS Monoplex. You've agreed that they can tolerate the planned
outages required for such tasks as z/OS release upgrades in that LPAR
(perhaps scheduled in conjunction with a DR rehearsal), that the unplanned
outage characteristics (which are still quite excellent, as long as the
site is available) are good enough to meet the business requirements, and
that VSAM RLS and Transactional VSAM technologies are required to make sure
that the applications are providing excellent concurrent online and batch
services, to avoid planned online outages to run batch jobs. If these
parameters meet your needs, great, you're all set. There's a wonderful,
value-packed configuration for you called a z/OS Monoplex with VSAM RLS and
Transactional VSAM. If you change your mind, and management wants a
different service level, no problem! Gracefully shift to a Parallel Sysplex
with two z/OS LPARs on one machine, as one example. Or to any of the many
other configuration options available, as/when they make sense to deliver
on particular end-to-end business service needs.
>The white paper clearly describes some structures as demanding
>duplexing or third CPC with failure-isolated CF.
Yes, but David Raften is only describing the technical attributes there.
He's not necessarily describing business service outcomes, which require
more analysis. A particular technical result may or may not matter in terms
of delivering on particular end-to-end business service goals. "It
depends."
(*) Which is not quite the same as saying you need a CF *engine*. The CFCC
can run on a general purpose engine, and occasionally that makes sense.
--------------------------------------------------------------------------------------------------------
Timothy Sipples
IT Architect Executive, Industry Solutions, IBM Z & LinuxONE,
Multi-Geography
E-Mail: [email protected]
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