Winston, thanks for the reply. What do you mean by "One CommServ servers (the correct technical terminology): DC1CV1 <--> DB mirror <--> DC2CV2" (That still looks like two CommServ servers to me).
Also, regarding licensing,
I found [https://documentation.commvault.com/commvault/release_9_0_0/books_online_1/english_us/prod_info/dedup_disk.htm?var1=https://documentation.commvault.com/commvault/release_9_0_0/books_online_1/english_us/features/dash_copy/dash_copy_basic.htm]
DASH Copy requires following licenses based on the License Type:
For Traditional License, Block Level Deduplication license is required on the MediaAgent hosting the deduplication store.
For License Usage by Capacity, Data Protection Enterprise (for Backup) or Archive Enterprise (for Archive) license is required.
Looks like if CommServ relies upon SQL database mirroring, then the SQL Server Enterprise Edition would be a requirement. Please see [https://docs.microsoft.com/en-us/sql/database-engine/database-mirroring/prerequisites-restrictions-and-recommendations-for-database-mirroring?redirectedfrom=MSDN&view=sql-server-2017] and [https://docs.microsoft.com/en-us/sql/sql-server/editions-and-components-of-sql-server-2016?view=sql-server-2017#RDBMSHA] and [https://docs.microsoft.com/en-us/sql/database-engine/database-mirroring/database-mirroring-operating-modes?view=sql-server-2017].
Optimal database mirroring performance is obtained by using asynchronous operation... Most editions of SQL Server 2017 support only synchronous database mirroring ("Safety Full Only"). For information about editions that fully support database mirroring, see "High Availability (Always On)" ...
My interpretation is only Enterprise Edition supports asynchronous operations aka "High Availability (Always On)".