No, that’s not exactly how it works. The max for the cluster would still be the same, aka 40K. If you have a need for a bigger cluster you’ll need to work with Cisco to create a mega cluster that can scale beyond the normal levels.
No that’s not how it works.
The first would support 10K as you have 2 CPE, one active and one redundant.
The second would support 20K, 10K on 2 CPEs and the 3rd would be used for 2 to 1 redundancy. If two CPE fails the max would be 10K.
The third would support 40K, with 4 being active and 4 being used to provide redundancy in a 1 to 1 manner.
Based on this and other questions you post I would recommend you to read the SRND. Most of your queries have an answer in this document.
One reflection, I think that I saw somewhere that you said that your working on writing a book on the topic that your questions are about. If you have a need to ask all these questions I would think that you should maybe not do that. Just my 2 cents on this.
My bad then and good for you. Anyway read the SRND will still be my strong recommendation.
Even if you use 8 Call processing nodes, the maximum capacity of the Cluster is 40K endpoints. If you want to register more endpoints or if you more subscriber nodes you need a megacluster. Refer Megacluster section on SRND.
The below thread about megacluster will be useful.
https://community.cisco.com/t5/unified-communications/cisco-mega-cluster/td-p/3473283
This is the outtake on the topic from the 12.5 SRND. It’s pretty straightforward and clear IMHO.
Virtual Nodes and Cluster Maximums
The sizing tool applies the following server node and cluster maximums. These values can vary depending on Unified CM software version:
- Each cluster can support configuration and registration for a maximum of 40,000 secured or unsecured SCCP or SIP phones.
- Two TFTP server nodes are required, in addition to a dedicated publisher, if the number of endpoints in the cluster exceeds 1,250.
- Support for CTI connections has improved over the last several releases, and each cluster can support a maximum of 40,000 CTI connections.
- The number of call processing subscribers in a cluster cannot exceed 4, plus 4 standby, for a total of 8 call processing subscriber nodes. Also, the total number of server nodes in a cluster, including the publisher, TFTP, and media servers, may not exceed 21 servers as the maximum allowed in a cluster.
The SRND is clear on that, it is 40K. It doesn’t matter what tricks you try to do with clever things in configuration, it is still the same.
In a normal cluster, ie not a mega cluster, at any given time there can not be more than 4 active call processing nodes. This is clearly stated in the outtake I posted before, but for completion I’ll post that specific part once more.
“The number of call processing subscribers in a cluster cannot exceed 4, plus 4 standby, for a total of 8 call processing subscriber nodes.”
The fact that this says that you can have 4 in standby is key for you to grasp based on your questions. The key word in this is standby, they cannot be active as CPE nodes at the same time as the primary.
