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SQL Server 2012 Always On

SQL Server 2012 Always On. Lisa Gardner. Premier Field Engineer. Microsoft Corporation. http://blogs.msdn.com/sqlgardner. High Availability Outcome Options. Understanding of High Availability Options in SQL Server 2012 Benefits of AlwaysOn HA design patterns utilizing AlwaysOn. Agenda.

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SQL Server 2012 Always On

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  1. SQL Server 2012 Always On Lisa Gardner Premier Field Engineer Microsoft Corporation http://blogs.msdn.com/sqlgardner

  2. High Availability OutcomeOptions • Understanding of High Availability Options in SQL Server 2012 • Benefits of AlwaysOn • HA design patterns utilizing AlwaysOn

  3. Agenda • High Availability Options • AlwaysOn Demo • Readable Secondaries • Readable Secondaries Demo • AlwaysOn Design Patterns

  4. High Availability Options • Pre-SQL Server 2012 • What's New in SQL Server Failover Clustering? • SQL Server 2012 AlwaysOn

  5. Pre-SQL Server 2012 High Availability Options • Backup/Restore • Windows/SQL Server Failover Clustering • Log Shipping • Database Mirroring • Third Party • SAN Replication

  6. AlwaysOn Technologies – Managed by WSFC

  7. What’s New in SQL Server Failover Clustering? • AlwaysOn Failover Cluster Instance provides instance level failover • Key SQL Server 2012 Clustering Enhancements • Multi-site geo-clustering across subnets • Flexible Failover Policy • Improved system diagnostics • Support for network attached storage(NAS) user SMB • Support for TempDB on local drive (SSD)

  8. Flexible Failover Policy (SQL Server 2012) • Control over when automatic failover should be initiated • Configurable options eliminate false failover • Improved logging for better diagnostics • New Cluster Properties • HealthCheckTimeout • FailureConditionLevel

  9. Failure Condition Levels 5 – Failover or restart on any qualified failure conditions Query Processing errors 4 – Failover or restart on moderate SQL Server errors Resource errors 3 – Failover or restart on critical SQL Server errors System errors 2 – Failover or restart on server unresponsive No response from sp_server_diagnostics 1 – Failover or restart on server down Service is down 0 – No Automatic Failover or restart

  10. Always On Availability Groups • Allows a group of databases to failover as a logical unit • Utilizes Windows Failover Cluster to report health • Defines a primary instance and up to four secondary instances • Provides automatic client redirection

  11. AlwaysOn Concepts • Availability Group • Availability Replica • Availability Database • Availability Group Listener

  12. SQL Server High Availability Options Recap

  13. Demonstration Creating an Availability Group

  14. Readable Secondaries • Mirrored copy of data on secondary server • Active Secondary servers provide off-loading functionality • Reading of data for reporting • Backups • DBCC • Connect via Instance name

  15. Active Secondary – Readable Routing • Allows for application to specify read Intent on Connection • ApplicationIntent– A New Connection Property • Connect via listener • Read-Only Routing • Optimized for automatic routing of read only applications • Routes must be create created manually

  16. Readable Secondary – Data Latency • Secondary reads are behind primary • Log is first hardened and then applied • Redo thread is asynchronous and runs in the background • Latency (typically seconds) can be larger for log intensive operations like bulk import or index create/rebuild • Sync Replica minimizes latency due to network issues

  17. Demonstration Leveraging Active Secondaries

  18. Query Performance on Secondary • SQL Server Uses Cost based optimizer • Relies on object Statistics • If statistics are missing SQL Server creates and persists • Auto-stat on readable secondary will require updates?

  19. Active Secondary : Enabling Backup on Secondary • Backups can be done on any replica • Must be able to communicate with primary • Log backups done on all replicas form a single log chain • Send all backups to a single UNC path • Database Recovery advisor makes restores simple • Must include backups from other instances manually • Differential Backups are not supported • Copy-Only backups are the only type • I have a 4 part blog series on this topic for more details

  20. AlwaysOn Troubleshooting • AlwaysOn Dashboard • Sp_server_diagnostics • Catalog Views Examples • Sys.availability_groups • Sys.availability_replicas • DMV are named sys.dm_hadr* • New Performance Monitor Counter Objects • SQLServer:Database Replica • SQLServer:Availability Replica • New Information Logged to the System Event Logs

  21. AlwaysOn Design Patterns • White Board/Flip Discussion

  22. Questions?

  23. Conclusion • AlwaysOn provides many High Availability Options • Enables Multi Site Failover with minimal effort • Allows maintenance and read activity to be distributed

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