The Question is:
I want to have on on-line contingency between these 2 servers. The alternative
should be able to fall over to another server with the most updated
We know they can both cluster together but are not sure if the volume shadowing
product is able to accomplish what we expect. I was told that both servers
require to have exact disk types/configurations.
Is this correct ? If so that means I can't use our old 2100 for a fall over
contingency without losing a complete day of transactions.
The Answer is :
It appears you are mixing the typical fully-live operations expected
of an OpenVMS Cluster configuration with the a primitive failover-based
With OpenVMS and OpenVMS Cluster configurations, all servers are
active and all are operating in parallel, with a configuration that
is normally designed to provide graceful degradation on failures.
(This means you get some use out of all of your servers, and you
know when you are operating in a degraded mode, and you know that
all of your servers are functioning -- an attempt to failover to
a server that is discovered non-functional is a situation to be
Host-based volume shadowing provides remote shadowing (mirroring) and
full write-sharing within an OpenVMS Cluster environment. This avoids
the degradation problems that can arise when a RAID controller becomes
unavailable, because the host-based shadowing product permits the data
to be shadowed (mirrored) across servers, and across geographic areas.
Data Replication Manager (DRM) is the closest hardware analog to the
capabilities of host-based volume shadowing, and there are differences.
DRM typically supports wider geographic distributions than does the
OpenVMS Cluster configuration, but shared and parallel access to the
various mirrored volumes is not available; all I/O access must go to
As for failover, the hardware configuration need only be identical if
the failover processing or if the local software requires it -- in the
more primitive failover-based schemes, similar or even duplicate
configurations can be necessary. In the case of a typical OpenVMS
Cluster configuration, each server is already configured and running,
so there is no particular need to have similar hardware configurations.
You do, of course, need to have sufficient processing and storage
resources available for any operations during the degraded (failure)
You will want to review the available materials on the OpenVMS Cluster
software -- there is extensive documentation in the OpenVMS manual
set -- and you will want to review the available materials on clusters
and at the related Disaster-Tolerant Cluster Services (DTCS) details
Compaq can offer services to help you configure your cluster for
disaster-tolerance, with experience in ensuring the necessary power
sources are available, proper networking hardware and communications
cable routing, lighting, graceful failover policies and procedures,
and related -- designing and setting up an OpenVMS cluster can be
quite easy; properly designing and implementing a disaster-tolerant
configuration is seldom a trivial undertaking. The DTCS Services