The Microsoft Exchange Team released an important update of the Exchange Mailbox Role Calculator, bringing it to version 12.8.

This version includes the following fixes since 12.3:

• Fixed total number of databases/server calculation to deal with Active/Active (Single DAG) scenario correctly with respect to dedicated DR servers
• Fixed storage design disk calculations formulas for Active/Active (Single DAG) scenario, i.e., don’t recommend JBOD in scenario where only single copy is deployed (e.g., lagged copy deployed in secondary datacenter without dedicated hardware)
• Fixed Number of Active Mailbox Servers in DC2 calculation to not double count lagged copies when deploying Active/Active (Single DAG) scenario and deploying lagged copy in both Primary and Secondary Datacenters
• Fixed # of Target Lagged Copy Log Stream calculations to not double count lagged copies when deploying Active/Active (Single DAG) scenario and deploying lagged copy in both Primary and Secondary Datacenters
• Fixed second DAG Member Layout Table to show number of servers for both Active/Active scenarios

Consult the changeblog here.You can download the calculator here. Usage instructions can be found here.