0. High Availability & Disaster Recovery with SQL Server AlwaysOn Availability Groups
Turgay Sahtiyan
Microsoft – Senior SQL Server PFE
© 2012 Microsoft Corporation Microsoft Confidential

1. Sponsors

2. Turgay Sahtiyan Istanbul, Turkey
Microsoft GBS Team - Senior SQL Server PFE
+12 years IT experience / Last 8 years SQL Server
Key areas : HA&DR Solutions, Performance Tuning, PDW
Community geek
Founder and Former President of SQLPass Turkey Chapter
Former SQL Server MVP
Speaker / Writer / Presenter at Microsoft & SQLSaturdays & Local User Groups
Social Media
Twitter
Blog :
Linkedin :
© 2012 Microsoft Corporation Microsoft Confidential

3. Agenda Current HA&DR Solutions SQL Server AlwaysOn Availability Group
Limitations of Current HA/DR Solutions
SQL Server AlwaysOn Availability Group
Client Failover using Virtual Network Name
Readable Secondary – ReadOnly Routing
Backup on Secondary Replicas
Availability Group Scenarios
Comparison of SQL Server HA&DR Solutions
Demo – AlwaysOn Aavailability Group
Real-Life Customer Scenario
What’s Coming with SQL Server 2014
© 2012 Microsoft Corporation Microsoft Confidential

4. SQL Server High Availability
HA&DR solutions before SQL Server 2012 AlwaysOn
Database Mirroring
Failover Cluster Instance
Log Shipping
These features help the customer to reach enough HA&DR but..
Customers demand more
Better Availability
Higher ROI
Simplicity
© 2012 Microsoft Corporation Microsoft Confidential

5. Failover Cluster Instance level redundancy Local or Remote Site
Presents VNN
Automatic Failover
Does not protect against data loss
Public
SQL Server Instance
SQL Server Instance
Shared Storage
© 2012 Microsoft Corporation Microsoft Confidential

6. Transaction Log Stream
Database Mirroring
Witness Server
Provide “a” redundant copy of database
Local or remote side
Works by sending TLog records
Connections are accepted only to the principal database
No VNN
Automatic failover with Witness Server
Principal Server
Mirror Server
Transaction Log Stream
Principal Database
Mirror Database
Client
© 2012 Microsoft Corporation Microsoft Confidential

7. Log Shipping
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8. Failover Clustering and Database Mirroring
Asynchronous Database
Mirroring
Secondary
Data Center
Primary
Data Center
SQL Server 2008 R2
Failover Cluster
SQL Server 2008 R2
Failover Cluster
Asynchronous Data Movement with Database Mirroring
© 2012 Microsoft Corporation Microsoft Confidential

9. Database Mirroring and Log Shipping
Disaster Recovery
Datacenter2
Primary
Datacenter
Log Shipping
Witness
SQL Server 2008 R2
Disaster Recovery
Datacenter1
SQL Server 2008 R2
Database Mirroring
SQL Server 2008 R2
Log Shipping
Synchronous Data Movement with Database Mirroring
© 2012 Microsoft Corporation Microsoft Confidential

10. Limitations of Current HA/DR Solutions
Solutions are fragmented
Database mirroring does not allow multiple secondaries
Multiple databases cannot fail over as a group
Log shipping might lose data and does not fail over automatically
Passive servers are mostly running idle
Offloading of reporting and maintenance tasks from the primary server is not easy
SAN is a single point of failure in failover clustering
© 2012 Microsoft Corporation Microsoft Confidential

11. SQL Server AlwaysOn: Features
Availability Groups
for Database Protection
New in SQL Server 2012 with:
Multiple database failover
Multiple secondaries
Active secondaries
Fast application failover
Integrated high-availability management
AlwaysOn
Failover Cluster Instances
for Instance Level Protection
Enhanced in SQL Server 2012 with:
Multi-subnet clustering
Flexible failover policies
Improved diagnostics
Faster failover
TempDB on local drives
Availability Groups and Failover Cluster Instances rely on Windows Server failover clustering, which provides a robust and reliable high-availability platform
© 2012 Microsoft Corporation Microsoft Confidential

12. AlwaysOn Availability Groups
Multiple Secondaries to Improve Redundancy
Up to 4
Max 2 Sync
© 2012 Microsoft Corporation Microsoft Confidential

13. AlwaysOn Availability Groups
Multiple Secondaries to Improve Redundancy
Up to 4
Max 2 Sync
Active Secondaries
Offloading read workloads
Backups on Secondary
© 2012 Microsoft Corporation Microsoft Confidential

14. AlwaysOn Availability Groups
Multiple Secondaries to Improve Redundancy
Up to 4
Max 2 Sync
Active Secondaries
Offloading read workloads
Backups on Secondary
Multiple Database Failover
© 2012 Microsoft Corporation Microsoft Confidential

15. AlwaysOn Availability Groups
Multiple Secondaries to Improve Redundancy
Up to 4
Max 2 Sync
Active Secondaries
Offloading read workloads
Backups on Secondary
Multiple Database Failover
Automatic Failover
Flexible Failover Policies for Greater Control over Failover
© 2012 Microsoft Corporation Microsoft Confidential

16. AlwaysOn Availability Groups
Multiple Secondaries to Improve Redundancy
Up to 4
Max 2 Sync
Active Secondaries
Offloading read workloads
Backups on Secondary
Multiple Database Failover
Automatic Failover
Flexible Failover Policies for Greater Control over Failover
Virtual Network Name (Listeners)
© 2012 Microsoft Corporation Microsoft Confidential

17. AlwaysOn Availability Groups
Primary
Data Center
Reports A
Secondary
Replica 1
Replica 3
Replica 2
Replica 4
Backups
Multiple Secondaries to Improve Redundancy
Up to 4
Max 2 Sync
Active Secondaries
Offloading read workloads
Backups on Secondary
Multiple Database Failover
Automatic Failover
Flexible Failover Policies for Greater Control over Failover
Virtual Network Name (Listeners)
© 2012 Microsoft Corporation Microsoft Confidential

18. Client Failover using Virtual Name
Availability Group Virtual Name allow applications to failover seamlessly on availability group failover
Application reconnects using a virtual name after a failover to a secondary
ServerA
ServerB
ServerC
HRDB
HRDB
HRDB
AGHR
HRVNN
Primary
Secondary
Primary
Secondary
Secondary
Application retry during failover
Connect to new primary once
failover is complete
and the virtual name is online
-server HRVNN;-catalog HRDB
© 2012 Microsoft Corporation Microsoft Confidential

19. Readable Secondary
DB2
DB1
SQLservr.exe
InstanceA
Primary
Secondary
Database Log Synchronization
InstanceB
Reports
Readable secondary allow offloading read queries to secondary
Close to real-time data, latency of log synchronization impact data freshness
Backup ve DBCC CheckDB operations can be done on secondary
© 2012 Microsoft Corporation Microsoft Confidential

20. Active Secondary : Read-only Routing
ApplicationIntent – A New Connection Property
Used to get access to secondary
Applicable when Secondary Replica set with ALLOW_CONNECTIONS =READ_ONLY or YES (ALL)
Connection String
Connect to primary replica
Server=myListener; Database=DB1;
Connect directly to a secondary instance
Server=myListener; Database=DB1; ApplicationIntent = ReadOnly
Read-Only Routing
Connection behavior optimized for automatic routing of read only applications to secondary
You have to create the routes manually for this to work
© 2012 Microsoft Corporation Microsoft Confidential

21. Active Secondary : Read-only Routing
© 2012 Microsoft Corporation Microsoft Confidential

22. Microsoft Confidential
Read-only Routing
ServerA
ServerB
AGHR
HRDB
HRDB
Primary
Secondary
HRVNN
Reports
OLTP
-server HRVNN;-catalog HRDB
-server HRVNN;-catalog HRDB; ApplicationIntent = ReadOnly
Microsoft Confidential
© 2012 Microsoft Corporation Microsoft Confidential

23. Microsoft Confidential
Read-only Routing
ServerA
ServerB
AGHR
HRDB
HRDB
Secondary
Primary
HRVNN
Reports
OLTP
-server HRVNN;-catalog HRDB
-server HRVNN;-catalog HRDB; ApplicationIntent = ReadOnly
Microsoft Confidential

24. Backup on Secondary Replicas
Backups can be done on any replica of a database
Log backups done on all replicas form a single log chain
Backups on primary replica still works
Supported backup types on secondary:
Full - COPY_ONLY method is only one supported Availability Replica
Transaction Log
Differential - Not Supported
Backup Preference
Prefer Secondary
Secondary Only
Primary
Any Replica
sys.fn_hadr_backup_is_preferred_replica
© 2012 Microsoft Corporation Microsoft Confidential

25. Availability Group Scenarios
Direct Attached Storage local, regional and geo secondaries
Availability Group provides redundancy for databases on both standalone instances and failover cluster instances
Shared Storage, regional and geo secondaries A
Synchronize
Asynchronize
© 2012 Microsoft Corporation Microsoft Confidential

26. Microsoft Confidential
Comparison of SQL Server High-Availability and Disaster-Recovery Solutions
Technology
AlwaysOn
Failover Clustering Instances
AlwaysOn Availability Groups
Database Mirroring
Log Shipping
Zero data loss
 *
 **
Instance Redundancy 
Database Redundancy
Auto Failover
Readable Copy
 ***
 ****
Multiple Secondaries
Notes:
* Zero data loss is possible with AlwaysOn failover clustering instances only when combined with synchronous SAN replication or synchronous AlwaysOn Availability Groups and /database mirroring.
** Zero data loss and automatic failover are possible with synchronous AlwaysOn Availability Groups and database mirroring.
*** The mirror database itself is not directly readable, but a static, point-in-time view of it can be read by using a database snapshot.
**** The log shipping secondary database can be read when the transaction log backups are restored by using the WITH STANDBY option.
Note: Database mirroring is available and supported in SQL Server But AlwaysOn Availability Group is the primary high-availability and disaster-recovery feature for databases, and Microsoft plans for it to replace database-mirroring technology. Peer-to-peer replication is the primary solution for scenarios that need multi-site updates and multi-master replication. Log shipping is supported in SQL Server For additional information about support for database mirroring, see “Features Not Supported in a Future Version of SQL Server” (
Microsoft Confidential
© 2012 Microsoft Corporation Microsoft Confidential

27. Demo myListener Secondary Data Center Primary Data Center Replica 3
Synchronize
Asynchronize A
Secondary
Data Center
Primary
Data Center
Replica 3
Reports
Replica 2
Replica 1
myListener
© 2012 Microsoft Corporation Microsoft Confidential

28. Real-Life Customer Scenario
Primary
Data Center A
FCI A
Secondary
Data Center A
Reports
Backups
Backups
Synchronize
Asynchronize
© 2012 Microsoft Corporation Microsoft Confidential

29. What’s Coming with SQL Server 2014
Increase number of secondaries to 8 (from 4)
Increase availability of Readable Secondaries
Use readable secondaries despite network failures (important in geo-distributed environments)
AlwaysOn Availability Groups Add Azure Replica Wizard
Support for Windows Server 2012 Cluster Shared Volumes (CSV)
Enhanced Diagnostics
© 2012 Microsoft Corporation Microsoft Confidential

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