[Info-vax] Third node into 2-node cluster

[Stephen Hoffman]

On 2019-03-28 16:07:49 +0000, Dave Froble said:

> I do not understand any of the logic on having a third node that is not 
> a full member of the cluster.  Assuming that it has a cluster license, 
> why would you not then make full use of it.

The third host is a full member, and may or may not be used for processing.

The less-expensive approach for the two-host configuration is a shared 
storage interconnect and a quorum disk.

> Regardless of the initial goal of doing away with the quorum disk, 
> you've now made a sizable investment, and to not take full advantage of 
> it just doesn't make sense.  To me anyway.

As David comments, I'd also usually look to use the third host for 
processing, though that can require application changes.

But...   Some apps cluster, and some don't.

And as the I/O load increases or the available access timing decreases, 
trying to process data across a LAN may not be the best or even the 
right choice.

Which gets back to a shared storage I/O interconnect or a cluster 
communications interconnect, or efforts toward load shedding or load 
sharding.

For the apps that aren't or that can't be reasonably made cluster 
aware, or for apps that might run entirely from memory with logging for 
persistence, a cluster configuration as a hot or a warm standby would 
be an option.

Downtime costs and budgets vary as much as app requirements and app 
limitations, too.



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