SQL Server® AlwaysOn (HADRON)

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Technical Leader, Microsoft Database Support Team

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Windows Server ® Failover Clustering (WSFC)

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Multi-node w/Shared Data Storage

SQL Binaries on each node

Client Connections via Virtual Server Name

Manual or Automatic Instance Failover

Stretch Cluster via VLAN

AlwaysOn Failover Cluster Instances (FCI)

Flexible Failover Policy

sp_server_diagnostics logging

Multi-Subnet Failover Cluster

Faster Recovery with Indirect Checkpoints

Shared Data Disk

Log Shipping

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Provides Remote Disaster Recovery Site

Database Level Protection

Based on Transaction Log Backup\Restore

Easy to setup

No Automatic Failover

No Client Redirection

Database Mirroring

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Hot Disaster Recovery Site for Single Database

Easy setup using Wizard per Database

Synchronous Mirroring

Automatic Failover via 3rd Witness Server

Client Redirection

Asynchronous Mirror

Automatic Page Repair (2008)

Log Stream Compression (2008)

Mirror Backups (2008)

New for SQL Server 2012

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Primary ReplicaData Changes

SynchronousHot DRStandby

AsynchronousWarm StandbyReadableReports

AsynchronousWarm StandbyReadableBackups

Log Shipping + Database Mirroring

+ Windows Clustering =

AlwaysOnAvailability Group

for Database Protection

from Windows Server Failover Cluster (WSFC)

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Automatic Failover via Windows Server Failover Cluster (WSFC)

Flexible Failover Policy using sp_server_diagnostics

Multisite Clustering using disbursed servers

Multiple Secondary Nodes (up to four)

Virtual Server Name for Client Redirection (availability group listener)

Enhanced

No shared disk storage used in Windows Clustering

No restart of SQL resulting in faster failover

Failover single, or group of databases instead of entire SQL Server

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from Database Mirroring

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Two Synchronous Secondary Servers for high availability

Backup Asynchronous Secondary Servers (total 4)

Automatic Bi-Directional Page Repair

Secondary Backup (SQL 2008 EE)

Enhanced

Log Backup maintains backup chain allowing restore to Primary

Maintenance Plans “preferred backup” based on “priority”

Bi-directional automatic page repair

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SQL Server 2012 Management Studio

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Availability GroupParticipating SQL instances, their roles and corresponding properties

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Availability Replica Unit of failover.

Single database or group of databases

Group ListenersSingle Name Connection

AlwaysOn Architecture

Windows Server Failover Clustering (WSFC) Cluster

Network Subnet

NodeNode

SQL Server Instance

Storage

Node

Network Subnet

Node

SQL Server Instance

Storage

Node

SQL Server Instance

Storage

SQL Server Failover Cluster Instance

Shared Storage

AlwaysOn Availability Group

Instance Network Name

Instance Network Name

Instance Network Name

Instance Network Name

Secondary Replica

Secondary Replica

Secondary Replica

Primary Replica

AG Listener Virtual Network Name

WSFC Quorum Witness Remote File Share

WSFC Configuration

WSFC Configuration

WSFC Configuration

WSFC Configuration

WSFC Configuration

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Availability Group Configuration• Up to 5 replicas (including primary)

• Availability Mode• Asynchronous

• Synchronous• Up to 3 replica per availability group including primary

• Failover mode• Manual

• Automatic• Up to 2 per availability group

• Requires synchronous availability mode

• Readable Secondary• No

• Yes

• Read Intent

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AVAILABILITY GROUP AVAILABILITY MODE

•Asynchronous• Primary replica doesn’t wait for secondary replicas to harden log

records.

• Performance over data protection

• Secondary never synchronized / can lag behind

• Reports ‘synchronizing’, never ‘synchronized’

• Useful• When availability replicas are distributed

• Transaction performance is priority

• Synchronous• Primary commit waits for secondary log harden

• Synchronized data protection over performance

• High availability over performance

• Reports ‘synchronizing’ or ‘synchronized’

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AVAILABILITY GROUP FAILOVER MODE

• AUTOMATIC• Requires synchronous availability mode

• Up to two availability replica

• Additional configuration options• HEALTH_CHECK_TIMEOUT

• FAILURE_CONDITION_LEVEL

• MANUAL• Asynchronous or synchronous availability mode

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Types of Failover

Three Types of Failover

• Automatic• Synchronous Commit

• Automatic Failover

• Replica in SYNCHRONIZED state

• Planned manual failover (without data oss)• No data loss - supported when synchronous commit and secondary is

‘synchronized’

• alter availability group agtest1 failover

Forced manual failover (with possible data loss)• Supported with asynchronous commit

• Secondary is synchronizing or not_synchronized

• alter availability group agtest1 force_failover_allow_data_loss

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AlwaysOn Readable Secondaries

•Secondary Replica is ‘Active’

•Offload Read Only activity• Backups• DBCC CHECKDB• Read Only querying, reporting

• How do you re-direct read-only activity?

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AlwaysOn Readable Secondaries

Configure secondary for read access

CREATE AVAILABILITY GROUP REPLICA ON

‘SQL01' WITH

(…SECONDARY_ROLE=…)

- NO

- ALL

- READ_ONLY

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AlwaysOn Readable Secondaries

• Read-Only client connection behavior determined by Availability Replica Option+ ApplicationIntent Property

• READ ONLY ROUTING1. Secondary replica read access

• SECONDARY_ROLE

2. Set replica’s URL for secondary routing• READ_ONLY_ROUTING_URL

3. When primary, replica routing list• READ_ONLY_ROUTING_LIST

4. Application connects using listener

5. Application use ReadOnly to connect

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AlwaysOn Backup on Secondary

• Why backup on secondary?• Backup is resource intensive

• Offload job from Tier-1 application

• What is supported:• BACKUP DATABASE (copy-only full backup)

• BACKUP LOG

• Differential not supported

• Offload backups to synchronized or synchronizing secondaries

• Manage backups with new Recovery Advisor

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Mulit-Subnet Failover

•No VPN needed•No storage replication•Multi IP address• ‘OR’ dependency

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Keywords for Multi-Subnet AG

• RegisterAllProvidersIP

- Get rid of DNS issue

• MultiSubnetFailover

- Quick establish connection

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