Hi Suresh,
1) With synchronous mirroring, the primary server only confirms the transaction after the acknowledge from the mirrored server is received. Considering that both IO subsystem and network bandwidth/distance of primary and mirrored are well taken care, still there can be delays in database updates (and possibly batches). Dialog is not much affected, because the way SAP ABAP AS works with asynchronous database updates.JAVA on the other hand can be affected, because the logic is different.
2) You have to decide to use synchronous mirroring with automatic failover or not.
I personally suggest you to upgrade your database to at least SQL Server 2012 and go for AlwaysOn. SQL Server 2008 R2 is 6 years old and there are 3 releases ahead of him (2012, 2014 and 2016). If you are to spent some effort with building a HADR solution, it would be better to build one that is currently supported, because as of SQL Server 2012, Database mirroring has been deprecated by Microsoft and might be removed in a future version.
You can get more details from Database Mirroring in the SAP on SQL Server whitepaper recently released at MSDN.
The following notes are also helpful:
1772688 - SQL Server AlwaysOn and SAP applications
965908 - SQL Server Database Mirroring and SAP Applications
Best regards,
Luis Darui
