[Info-vax] Wide area cluster, metro area network, seeking info

[Stephen Hoffman]

On 2021-06-08 22:28:49 +0000, Rich Jordan said:

> We are looking at the possibility of putting VMS boxes in two 
> locations, with Integrity boxes running VSI VMS.  This is the very 
> beginning of the research on the possibility of clustering those two 
> servers instead of just having them networked.  Probably have to be 
> master/slave since only two nodes and no shared storage.
> 
> After reviewing the various cluster docs, they seem to be focused on 
> older technologies like SoNET and DS3 using FDDI bridges (which would 
> allow shared storage).  The prospect has a metropolitan area network 
> but I do not have any specs on that as yet.
> 
> Are there available docs relevant to running a distributed VMS cluster 
> over a metro area network or fast/big enough VPN tunnel?  Or is that 
> just the straight cluster over IP configuration in the docs (which 
> we've never used) that we need to concentrate on?

Once the costs are understood and acceptable, then the design 
discussions and trade-offs can progress.

Get the prices, first. Before starting to investigate the design in any 
detail, get a quote from VSI for clustering and likely also for 
software RAID-1 (HBVS), and determine whether those costs are 
sustainable, and whether SaaS licensing or traditional licensing is 
preferred. Prior to the advent of SaaS licensing, the cluster license 
purchase prices alone ended more than a few of these project 
discussions.  Also for this case, get a quote for metropolitan Ethernet 
via SDN or MPLS or point-to-point microwave or whatever other similar 
connect the local comms carriers are offering.

Once you're over that purchasing hurdle, your design here is inherently 
going to be primary-secondary only (two hosts, with no shared storage), 
and your interconnect speed will be limited by the available link 
speeds and which particularly plays into software RAID-1 processing, 
and you'll need to discuss whether that'll meet your customer's 
clustering expectations. Primary-secondary also means manual 
intervention to promote the secondary to primary status, whether the 
primary is down or the link is down. And clustering usually means both 
sites drop offline if somebody or something clobbers the shared 
production data, whether that might have been an accidental or 
incidental or malicious corruption.

I prefer LAN clustering and network bridging to the IPCI clustering / 
NISCS_USE_UDP path as there are some other cluster-related options 
available only with a bridged LAN, though both interconnects can and do 
work.

Whichever you pick here, software RAID-1 needs beaucoup bandwidth or 
you'll be enjoying cascading failures.

Also review the DT (delirium tremens, err, disaster tolerance) 
alternatives. Splitting off volumes and a rotating schedule shipping 
those copies to the warm site can be cost-acceptable for some 
applications and environments.

The above assumes y'all are within maximum the clustering span; within 
500 mi / 800 km, as the wires were drug; as the electrons fly.








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