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AlwaysOn FAQ for SQL Server 2012


Look here for answers to frequently asked questions (FAQs) about AlwaysOn:



What is SQL Server AlwaysOn?

SQL Server AlwaysOn is the new comprehensive high availability (HA) and disaster recovery solution for SQL Server 2012. Using AlwaysOn, businesses can now achieve increased application availability and get better return on their hardware investments through a simplified HA deployment and management experience.

AlwaysOn comes with new and enhanced capabilities that can provide availability for specific application database(s) and also the entire instance which provides the flexibility to support various high availability configurations:

Both AlwaysOn Availability Group and AlwaysOn Failover Cluster Instance rely on Windows Server Failover Clustering infrastructure which provides a robust and reliable high availability platform.

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What is AlwaysOn Availability Group?

AlwaysOn Availability Group is the new capability that provides protection for application database(s). This capability not only provides all the functionality that current Database Mirroring capability provides but also comes with a rich set of options that improves database availability and also introduces capabilities that enable better resource utilization.

Note: From SQL Server 2012 and later releases, AlwaysOn Availability Group is the recommended HA capability for database availability.

The key availability options are:

  • Failover a group of databases.
  • Multiple secondaries for improved redundancy.
  • Two synchronous secondaries for better data protection.
  • Asynchronous active log synchronization for high latency networks.
  • Flexible Failover Policy for greater control over failover.
  • Automatic page repair for protection against page corruption.
  • Encryption and compression provides a secure, high performing transport.
  • Virtual name for fast application failover.

Active Secondary
Apart from the different availability options Availability Group introduces Active Secondary that enables improved utilization of secondary hardware. Active Secondary enables.

  • Offloading read workloads to a secondary instance.
  • Full and transaction log backup on a secondary instance.

These are options that can be set at the Availability Group for each of the secondaries.

Simplified Deployment and Management
Availability Group also comes with an integrated set of tools that simplifies high availability deployment and makes management of a complex topology very easy:

  • AlwaysOn Availability Group Wizard—Simplifies capturing high availability requirement and creation of availability group.
  • AlwaysOn Dashboard—Provides key system information that allow admins to make quick operational decisions and diagnose and troubleshoot problems.
  • AlwaysOn MOM pack for System Center—Enables using system center for monitoring SQL Server High Availability deployments.

AlwaysOn also provides full Powershell integration using new cmdlets that enables complete automation of Availability Group deployment.

In addition, AlwaysOn comes with a great set of troubleshooting tools that includes Dynamic Management Views (DMVs), performance monitor counters and extended events.

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What is AlwaysOn Failover Cluster Instance?

AlwaysOn failover cluster instance provides availability for the entire SQL Server instance by enabling failover of the instance rather than individual database(s).

AlwaysOn failover cluster instance enhances the existing SQL Server Failover Clustering with support for the following capabilities:

  • Multi-site clustering across subnets for improved site protection.
  • Flexible failover policy for better control over instance failover.
  • Improved diagnostics for faster troubleshooting.
  • tempdb on local drive allows better query performance.

Both AlwaysOn Availability Group and AlwaysOn Failover Cluster Instance rely on Windows Server Failover Clustering infrastructure which provides a robust and reliable high availability platform.

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What are the Other High Availability Enhancements in SQL Server 2012?

Apart from the new AlwaysOn solution, SQL Server 2012 provides support for Windows Server Core. This reduces OS patching and consequently system reboots which increases application availability by as much as 50-60%.

There are also enhancements to online operations and that now includes reindexing of LOB columns and addition of non-null columns which increases availability during application upgrade.

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Does AlwaysOn Availability Group replace database mirroring and other existing database high availability features in SQL Server 2012?

AlwaysOn Availability Group will be the primary high availability and disaster recovery feature for databases and will replace database mirroring technology over two releases. Database Mirroring will still be available as a feature in SQL Server 2012.

Peer-Peer replication will continue to be available in future releases and is the primary solution for scenarios requiring multi-site updates and multi-master replication. Log shipping will continue to be available in future releases.

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What are the AlwaysOn capabilities and options available in SQl Server 2012?

For SQL Server 2012, the following list of AlwaysOn capabilities and options are available.

AlwaysOn Availability Group with the following options

  • Failover a group of databases
  • Add a single secondary using the asynchronous availability mode
  • Force failover to the asynchronous secondary
  • Suspend and resume data movement
  • Enable the secondary for read and execute read query on the secondary
  • Create a virtual name for the availability group and have application connect using the virtual name
  • Configuring availability group using:
    • Transact-SQL statement
    • AlwaysOn wizard
    • Powershell cmdlets
  • Troubleshoot using DMVs, Performance Monitor Counters and Extended events

AlwaysOn Failover Cluster Instance Enhancements

  • Create a multi-site cluster across subnets
  • Enable flexible failover policy
  • Improved diagnostics

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