Professional Association for SQL Server

SQL Server 2012High Availability and DR

Joey D’Antoni

2200 GMT

Thank You to our Sponsors

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

Agenda

• SQL Server 2008 to 2012—What’s Changed in HA and DR

• Geo-Clustering• All about Availability Groups

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

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

Windows Core Support

• No GUI version of Windows• Allows for fewer patches• Uses PowerShell and MMCs for support

Windows Core

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*

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*

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

SQL Server Failover Clustering Architecture

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

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

Quorum

It’s not just bad cologne anymore

QuorumAre you there?

Why Yes I am here

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

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

Quorum Models

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

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

Why Do Clusters Failover?

• Initiated by failures in hardware or software

• Checked by isAlive/LooksAlive processes (in 2008R2 and below)

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

Flexible Failover Policies for Clusters

Level Condition Description

0 No automatic failover or restart

• Indicates that no failover or restart will be triggered automatically on any failure conditions.

1 Failover or restart on server down • SQL Server service is down.

2Failover or restart on server unresponsive

• SQL Server instance is not responsive (Resource DLL cannot receive data from sp_server_diagnostics within the HealthCheckTimeout settings).

3 (Default)Failover or restart on critical server errors

• System stored procedure sp_server_diagnostics returns ‘system error’. (Critical errors > 20)

4Failover or restart on moderate server errors

• System stored procedure sp_server_diagnostics returns ‘resource error’. (Moderate errors > 17)

5Failover or restart on any qualified failure conditions

• System stored procedure sp_server_diagnostics returns ‘query_processing error’. (Deadlock)

What is Stretch Clustering

• Also known as Geo-Clustering

Geo Cluster

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

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

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

AlwaysOn Availability Groups

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)

AlwaysOn Architecture

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

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

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

Failover Scenarios

Asynchronous-commit mode

Synchronous-commit mode with manual-failover mode

Synchronous-commit mode with automatic-failover mode

Automatic failover No No Yes

Manual failover No Yes Yes

Forced failover Yes Yes No

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

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

Client Connections

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

Turning On AlwaysOn

Availability Groups Demo

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

Contact Info

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

Thank You to our Sponsors