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SQL Server - AlwaysOn 2012 Vs. AlwaysOn 2014

By Saleem Hakani on 9/21/2014

AlwaysOn (Codename. Hadron ((High Availability Disaster Recovery Always On)) was introduced in SQL Server 2012. It’s one of the most powerful high availability technology introduced in SQL Server and is one of the compelling reasons to migrate to SQL Server 2012 that provides reliable, integrated, flexible and efficient high availability and disaster recovery solution. In brief, AlwaysOn availability groups enable HADR for multiple databases with the need of expensive SAN hardware and you can offload many tasks/operations like (Queries, Reporting, Backups, Maintenance, etc.) to the secondary replicas and Primary replica can be used for write purpose. Data is copied per log record from Primary to secondary servers either synchronously or asynchronously. 

SQL Server 2014 provides HADR for on premise, cloud and hybrid solution for AlwaysOn.

Here’s a table that shows some of the limitations of AlwaysOn between SQL 2012 and SQL 2014:

Feature / Capability

SQL Server 2012

SQL Server 014

Total nodes you can have in AlwaysOn

5

9

Maximum number of Secondary replicas

4

8

Failover partners

2

2

Synchronous Commit

3 (Including Primary)

3 (Including Primary)

Total # of Primary Replica

1

1

Total # of Secondary Replicas

4

8

Support for flexible failover policy

Yes

Yes

Automatic Page Repair

Yes

Yes

Read-workload on Secondary when Primary Replica is not available

No

Yes

Last Commit time available in DMV/Dashboard

No

Yes

AlwaysOn Diagnostics

Regular

Improved and add 20+ additional enhancements

*Routing table doesn’t work in this scenario. However, application can connect to the secondary replica if application connection string hard-code the server name.

AlwaysOn Comparison
HADR
HADRON
High Availability
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