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The AlwaysOn Availability Groups feature, first introduced in SQL Server 2012 and enhanced in SQL Server 2014, provides a high-availability and disaster-recovery solution for your SQL Server databases. This feature allows you to maximize availability for one or more user databases. In this post, we'll discuss best practices for setting up AlwaysOn Availability Groups across multiple data centers.

To begin, ensure that your SQL Server instances are using the same version and edition. For instance, if you are planning to use SQL Server 2014 Enterprise Edition, all replicas in your AlwaysOn Availability Group should be running this version. This ensures that all features and capabilities are consistent across your replicas.

For the configuration of your Availability Group, it is recommended to use a minimum of three replicas. One primary replica for read-write operations, a secondary replica in your primary data center for read-only operations and backups, and a secondary replica in a different data center for disaster recovery purposes. This configuration ensures that your system can continue to operate even in the event of a data center failure.

--Creating an Availability Group in SQL Server 2014
CREATE AVAILABILITY GROUP [AG1]
WITH (AUTOMATED_BACKUP_PREFERENCE = SECONDARY)
FOR DATABASE [DB1], [DB2]
REPLICA ON 
   'INSTANCE1' WITH (ENDPOINT_URL = 'TCP://INSTANCE1.domain.com:5022', 
   FAILOVER_MODE = AUTOMATIC, AVAILABILITY_MODE = SYNCHRONOUS_COMMIT, 
   BACKUP_PRIORITY = 50, SECONDARY_ROLE(ALLOW_CONNECTIONS = READ_ONLY)),
   'INSTANCE2' WITH (ENDPOINT_URL = 'TCP://INSTANCE2.domain.com:5022', 
   FAILOVER_MODE = AUTOMATIC, AVAILABILITY_MODE = SYNCHRONOUS_COMMIT, 
   BACKUP_PRIORITY = 50, SECONDARY_ROLE(ALLOW_CONNECTIONS = READ_ONLY));

For MySQL 5.6, replication is commonly used for high availability across data centers. However, MySQL does not provide an equivalent feature to SQL Server's AlwaysOn Availability Groups. Instead, you can utilize technologies such as MySQL Replication or Galera Cluster to achieve similar results. For DB2 10.5, you can use the DB2 HADR feature, which provides a high availability solution that protects against data loss by replicating data changes from a source database, called the primary, to a target database, called the standby.

If you are using Azure SQL, Azure provides built-in support for high availability and disaster recovery. You can configure Active Geo-Replication, which is a feature of Azure SQL Database that allows you to create readable secondary databases in the same or different data center (region). You can also use Auto-Failover Groups to manage the replication and failover of a group of databases.

In conclusion, while the specific technologies and steps may differ, the principles of setting up high availability across data centers remain largely the same. Ensure that you have at least one replica in a different data center to protect against data center-level failures, use the same versions and editions for all your SQL Server instances, and make use of the high availability features provided by your chosen database technology.