Always On AG- Readable Secondaries: How they work?

Readable Secondary AG databases internally use snapshot isolation under the covers. This will enable read-only workload to run against secondary databases.

http://www.sqldiablo.com/2012/08/01/alwayson-availability-groups-isolation-levels-selects-blocking-writers/

https://www.brentozar.com/archive/2014/01/careful-adding-indexes-with-alwayson-availability-groups/

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How to configure MSDTC as Clustered service (Windows 2008+)

https://blogs.technet.microsoft.com/askcore/2009/02/17/how-to-configure-multiple-instances-of-distributed-transaction-coordinator-dtc-on-a-windows-server-failover-cluster-2008/

http://sqlha.com/2013/03/12/how-to-properly-configure-dtc-for-clustered-instances-of-sql-server-with-windows-server-2008-r2/

http://www.michaelsteineke.com/post/2012/06/21/Clustered-DTC-and-Multiple-SQL-Instances.aspx

How many IP addresses are required for 2 node active-passive SQL Server failover cluster instance?

Total : 6 – 7

1 for WSFC cluster network name

1 for SQL Server instance network name

2 (1 on each node) for private/internal/heartbeat network among cluster nodes

2 (1 on each node) for public network access

1 for MSDTC (if MSDTC is configured as clustered service)

2 (1 for each node) for iSCSI HBA/network adapter for communication to SAN (if iSCSI SAN is used). 

HBA is used for offloading iSCSI TCP/IP traffic processing from CPU