I have a client who has a CUCM 7.1(x) cluster running on two MCS-7835-H2 servers. They use traditional licensing rather than CUWL.
They are planning to greatly expand the number of devices supported by the cluster so it would make sense to move to MCS7845 servers.
Is it possible to create a mixed server cluster where the 7845 servers act as Publisher and Subscribers and the 7835 servers are used for TFTP and MoH?
Even if this configuration is possible would it be supported by TAC?
It is possible to mix, and it is supported with some caveats. Here's what the SRND states:
While Cisco recommends using the same server model for all servers in a cluster, mixing server models within a cluster is supported provided that all of the individual hardware versions are supported and that all servers are running the same version of Unified CM. However, differences in capacity between various server models within a cluster must be considered because the overall cluster capacity might ultimately be dictated by the capacity of the smallest server within the cluster. Mixing servers from different vendors within a cluster is also supported and does not have any adverse capacity implications, provided that all servers in the cluster are the same model type.