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Cloud Series: High Availability in Azure SQL


Azure provides built in high availability. In a given server region, you are provided with three local copies of the Azure SQL Database.

Geo-Replication

Now, if there is an outage covering the entire server region, you can use the Geo-Restore feature or the Geo-replication feature to have a copy of the database in a different region. Geo-Replication offers up a 30 second RTO and a 5 second RPO. And rightfully so, since each secondary is billed at full price. It's a business decision as to how critical this database is.

One great benefit of Geo-Replication is that it can be used as a read-only database in addition to being on stand-by for failover. One can create up to four readable database replicas (much like SQL Server's always on in 2012).

Please keep in mind that Geo-replication only operates in asynchronous mode. Therefore there is a possibility of some data loss.

In fact the failover command even specifies data loss. If there is an unplanned outage:

ALTER DATABASE FORCE_FAILOVER_ALLOW_DATA_LOSS

Otherwise, it's a simple ALTER DATABASE FAILOVER (sound familiar) command for a planned outage.

DMVs

Look into the following DMVs and set up alerts for yourself to monitor the Geo-Replication health. I'll go into more in depth look at these in future posts.

sys.dm_operation_status

sys.geo_replication_links

sys.dm_geo_replication_link_status.

#azure #cloud #sqlserver #HighAvailability #DisasterRecovery #AlwaysOn