depends really on the number of users and the connection speed between the data centers.
Lots of solutions, but not knowing any of the details, it's hard to guess.
I suppose you could discuss this with a Symantec Systems Engineer, use the different sizing tools and what not to determine what kind of set up you should give them, I don't know what replaced SymIQ for Partners, but that should be your first stop
If i had to do it, without know anything about your environment i would have
Site A - With the most Users
EV10 SP4 on Windows Server 2012
- All Vault Stores and Indexes on storage local to that data center
- Vault Store Group hosted on the local SQL Server
SQL Server 2012 on Windows Server 2012 x64
- Hosting the Directory, Monitoring, Auditing Databases
- Hosting the Vault Store and Vault Store Group Databases for the EV Server located here
Site B - With the least users
EV10 SP4 on Windows Server 2012
- All Vaul Stores and indexes on storage local to that data center
- Vault Store Group hosted in Site B's SQL Server, not on the main directory SQL Server
SQL Server 2012 on Windows Server 2012
- Hosting the Vault Store and Vault Store Group Databases for the EV Server located here
You *could* have both Data Centers use the same SQL Server, and you could have both Data Centers use the same Vault Store Group, but that would add a lot of traffic to the WAN between the two sites, not just from SQL Calls back to the main data center, but from any shared parts that exist in the other sites vault store partitions.
On the flip side, you could also have it so each site mirrors each other, and if they do storage replication and SQL replication to each other, you can use the other DataCenter as disaster recovery.