1. Professional Association for SQL Server
SQL Server 2012
High Availability and DR
Joey D’Antoni
2200 GMT

2. Thank You to our Sponsors

3. About Me
• @jdanton on Twitter
• Principal Architect SQL Server, Comcast Cable
• Joedantoni.wordpress.com
• Videos and Blogs at SSWUG.org
• Vice President of the Philadelphia SQL Server User
Group
– SQL Saturday #121 Philadelphia—June 9th

4. Agenda
• SQL Server 2008 to 2012—What’s Changed in HA and
DR
• Geo-Clustering
• All about Availability Groups

5. Learning Objectives
• SQL Server HA and DR
• What’s involved in SQL Clustering
• How clustering and Availability Groups work
• What’s new in 2012 HA/DR

6. Licensing (What’s New)
• The Availability Group features will require the Enterprise
Edition of SQL Server
• The licensing model for SQL Enterprise Edition has
changed. Consult your friendly Microsoft sales
representative for more details
• AlwaysOn read-only replicas will need to be licensed

7. Windows Core Support
• No GUI version of Windows
• Allows for fewer patches
• Uses PowerShell and MMCs for support

8. Windows Core

9. High Availability (HA) and Disaster
Recovery (DR) Options in SQL 2008
• Backup and Recovery
• Failover Cluster Instances (FCI)
• Mirroring
• Log Shipping
• Replication
• SAN Replication*
• Virtualization*

10. High Availability (HA) and Disaster
Recovery (DR) Options in SQL Server 2012
• Backup and Recovery
• Failover Cluster Instances (FCI)
• Mirroring
• Availability Groups (2012)
• Log Shipping
• Replication
• SAN Replication*
• Virtualization*

11. What’s new in SQL Server 2012 HA/DR
• AlwaysOn Availability Groups
• SMB Support for Failover Cluster Instances
• Multi-subnet clustering is supported
• Flexible Failover

12. SQL Server Failover Clustering
Architecture

13. SQL Failover Clustering in 2008
• SQL Clustering required 1 subnet to be used across the
whole cluster
• Cluster failover is controlled by isAlive/looksAlive
processes, which check the SQL service and run
@@servername

14. SQL Failover Clustering in 2012
• Full support for geo-distributed clusters
• SMB Storage (File Shares) Supported for FCI
• Flexible failover model based on sp_server_diagnostics
• TempDB on Non-shared Disk Resource
– Makes PCI-based Solid State Drive an option

15. Quorum
It’s not just bad cologne
anymore

16. Quorum
Are you
there?
Why Yes I
am here

17. Understanding Quorum
• There are a several slides on this topic—it is critical!
– In a nutshell, you cluster has to be able to talk to itself to keep the
cluster service up in running
– This applies to both SQL Server Failover Cluster Instances and
AlwaysOn Availability Groups

18. Quorum
• Quorum is critical—contains master copy of the cluster’s
configuration
• Serves as a tiebreaker if network communications
between cluster nodes fail
• If Quorum fails—cluster is shut down until it’s restored

19. Quorum Models
• Node and Disk Majority (Default)
• Node Majority
• No Majority (Quorum Disk Only)
• Node and File Share Majority (Good for Geo Clusters)

20. Quorum Failure Tolerance
Number of Nodes 2 3 4 5 6 7
Node Majority 0 1 1 2 2 3
Node and Disk/File Share Majority 1 2 2 3 3 4
• Assuming Disk is Up Calculation is: Cluster Up = RoundUp(Total # of
Nodes/2)
• Assuming Disk is Down Calculation is: ClusterUp = RoundUp (Total # of
Nodes/2)-1

21. Why Do Clusters Failover?
• Initiated by failures
in hardware or
software
• Checked by
isAlive/LooksAlive
processes (in
2008R2 and below)

22. Flexible Failover—New for 2012
• Replaces looksAlive/isAlive functionality in SQL Clusters
(and is used for Availability Groups)
• Now runs sp_server_diagnostics
– Accepts two parameter
• HealthCheckTimeout (Default 60 sec/Minimum 15 sec)
• Failover Condition Level

23. Flexible Failover Policies for
Clusters
Level Condition Description
No automatic • Indicates that no failover or restart will be
0
failover or restart triggered automatically on any failure conditions.
Failover or restart
1 • SQL Server service is down.
on server down
• SQL Server instance is not responsive (Resource
Failover or restart
DLL cannot receive data from
2 on server
sp_server_diagnostics within the
unresponsive
HealthCheckTimeout settings).
Failover or restart
• System stored procedure sp_server_diagnostics
3 (Default) on critical server
returns ‘system error’. (Critical errors > 20)
errors
Failover or restart
• System stored procedure sp_server_diagnostics
4 on moderate server
returns ‘resource error’. (Moderate errors > 17)
errors
Failover or restart
• System stored procedure sp_server_diagnostics
5 on any qualified
returns ‘query_processing error’. (Deadlock)
failure conditions

24. What is Stretch Clustering
• Also known as Geo-Clustering

25. Geo Cluster

26. Geo-Distributed Clustering
• Requires SAN replication ($$$$)
• Two of everything
• Requires really fast network connection
• Requires some trickery at the network/DNS level for
connectivity
• Witness Disk (Quorum)
– Can be physical (SAN) disk, or cluster file share

27. Geo-distributed Failover Clustering
• Was available in SQL 2008, but easier to implement in
2012
• Won’t be used by most organizations due to cost and
complexity

28. Review—DR Options in SQL 2008
• Mirroring
– Allowed automatic failover, but only one target
– Mirror target is unreadable
• Log Shipping
– Allowed multiple targets, but failover a manual process, requiring a
connection string change
• Replication

29. AlwaysOn Availability Groups

30. AlwaysOn Requirements
• Windows Enterprise (Clustering is a requirement)
• SQL Server Enterprise Edition
• Windows Cluster
• No shared storage is required
• Quorum Disk (File Share if multi-site or local storage)

31. AlwaysOn Architecture

32. Flexible AG Failover
• Similar to how a failover clustered instance fails over
• Connects to instance every 30 seconds to perform health
check
• Also, similar quorum model to Windows Failover
Clustering

33. Allows for SAN-Less HA/DR
• This is not a huge thing for SQL Server in larger
organizations, but big win for medium sized businesses
• Allows much easier native SQL DR in Virtual
Environments

34. Considerations for Availability Groups
• All SQL servers (including the secondary in the
DR site) in the same Windows domain
• All the databases must be in FULL recovery
model
• The unit of failover (for local HA, as well as DR)
is at the AG level, i.e., group of databases – not
the instance

35. Failover Scenarios
Synchronous- Synchronous-
Asynchronous- commit mode with commit mode with
commit mode manual-failover automatic-failover
mode mode
Automatic failover No No Yes
Manual failover No Yes Yes
Forced failover Yes Yes No

36. Read Only Replicas
• Can have up to 3
• SQL Client 2012 will allow for this routing specifically
• Can take backups from read-only copies*
– Copy Only Backups (only full copy, does not affect primary log)
• Indexing must be same on replicas
• Bad queries can affect status of replica

37. Client Connections in This Model
• Availability Group Listener
– Works just like a failover clustering instance (single
instance, single IP)
– Creates a VCO (AD Virtual Computer Object)—similar to a cluster
virtual object
• Read-only Connections
– Requires 2012 native ODBC client

38. Client Connections

39. Client Connections
• Always specify Multi-Subnet Failover=True in listener
connection
• From Books Online
“will significantly reduce failover time
for single and multi-subnet AlwaysOn
topologies.”
• SQL Server Failover Cluster Instances as well

40. Turning On AlwaysOn

41. Availability Groups Demo

42. Summary
• Lots of Change in the HA/DR Space
• Licensing also changes—talk to your MS rep
• SQL Server Failover Clusters still a good HA option
• AlwaysOn Availability Groups add a lot more flexibility to
DR

43. Contact Info
• Twitter: @jdanton
• jdanton1@yahoo.com
• Blog: joedantoni.wordpress.com

44. Thank You to our Sponsors