SQL Server Denali - AlwaysON (HADR): Step-by-Setup setup guide

SQL Server Denali - AlwaysON (HADR): Step-by-Setup setup guide

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As you might be aware that SQL Server Code-Named “Denali” has introduced a new feature called Always ON for enhancing the availability of user database in a enterprise environment. In simple terms, AlwaysON is a high-availability and disaster recovery solution, which will enable you maximize availability of your critical user databases by use of “availability groups”

WARNING: The blog-post is based on pre-release software so things could change. For more details on CTP, please refer SQL Server Code-Named "Denali" CTP1 Release Notes

So what are “Availability Groups”?

Availability groups are set of failover partners (a.k.a availability replicas) to provide high availability to user database in Denali. Sure, this is lot more in depth and I suggest reading Denali Books-on-line for details.

In this blog post, I will guide you on how to configure AlwaysON – STEP-BY-STEP? Lets get going then !

Step 1. Windows OS and Cluster Configuration

a. For the purpose of testing, I have created a Windows 2008R2 two NODE cluster on virtual machine using Hyper-V and a Domain Controller

Machine configurations:

Machine Name

Role

OS

IP Address

INDNUKE- BANGALOREDC

Domain Controller

Windows 2008R2

192.168.1.1

INDNUKE- DELHI

Cluster Node 1

Windows 2008R2

192.168.1.2 Public
X.X.10.1
Heartbeat

INDNUKE-MUMBAI

Cluster Node 2

Windows 2008R2

192.168.1.3 Public
X.X.10.2
Heartbeat

If in case you need step-by-step guide on setting up windows cluster using Hyper-V (Guest Clustering), please refer my team blog:

http://blogs.msdn.com/blakhani/archive/2010/04/01/how-to-install-clustered-sql-server-2008-on-windows-2008-cluster-using-hyper-v-guest-clustering-part-1.aspx
http://blogs.msdn.com/blakhani/archive/2010/04/28/how-to-install-clustered-sql-server-2008-on-windows-2008-cluster-using-hyper-v-guest-clustering-part-2.aspx

Step 2. Install “Standalone” Denali instance on both the nodes

Yes, you’ve heard it right. AlwaysON is NOT a clustered SQL Server Instance. As such a standalone SQL Server setup is required on both the clustered nodes.

Standalone

I’ve installed 2 DEFAULT instances on both the clustered nodes as below:

INDNUKE-DELHI\MSSQLSERVER

INDNUKE-MUMBAI\MSSQLSERVER

Step 3. Enable AlwaysON feature on both the instances

•Open SQL Server Configuration Manager
•Select SQL Server Services
•Right-click on your SQL Server, in my case SQL Server (MSSQLSERVER) and select Properties
•Select SQL HADR TAB and check "Enable SQL HADR service"

clip_image002

Note: SQL Server service needs to be re-started for changes to take affect

Step 4. Create a sample database on both SQL Server Instances

For this testing, I will be using AdventureWorks sample database

Step 5. Create Availability Group

•Choose any one instance to become PRIMARY (say INDNUKE-DELHI\MSSQLSERVER)
•Open SQL Server Management Studio on INDNUKE-DELHI\MSSQLSERVER
•Expand Management folder
•Right-click Availability Groups and select New Availability Group

clip_image003

•Click Next on Introduction Screen

 New_availabilty_grp

•Provide a name to Availability Group

availability_grp_name

•Select the user database to be added to Availability Group

 select_database

•Specify Replicas – Add the other instances (INDNUKE-MUMBAI\MSSQLSERVER) to assume the role of secondary of this user database

 specify_replica_server

•Optionally, you can specify endpoint details (similar to database mirroring) or leave them default

 endpoints

•Summary Screen

 summary

•Result Screen

 result_screen

IMP: Once done, you will be able to see the Availability Group as a Cluster Resource in Windows Server Failover Cluster Manager

 availability_grp_as_cluster_resource

Step 6. Start Data Synchronization

•This step will allow you to synchronize your user PRIMARY and SECONDARY server by taking backup of user database and restoring this on secondary server 

 start_data_sync

•Specify a shared location, where both SQL Server start-up accounts has read/write access and press OK

•Once synchronization completes, expand the tree and you will be able to see the Availability Replicas (along with current role ) and Availability Databases

see_availibility_replica

 

Step 7. Test the Availability Groups

•To understand how failover functions in AlwaysON, follow simple steps

1. Create a simple table (can use below script) on PRIMARY (INDNUKE-DELHI) and insert some rows (can use below script)

Use AdventureWorks
GO

CREATE TABLE [dbo].[New_Table](
    [ID][int] NULL,
    [NAME] [varchar](50) NULL
) ON [PRIMARY]
GO

INSERT INTO dbo.New_Table values (5001, 'NORTH')
GO

SELECT * from dbo.New_Table
GO

 create_insert_on_demo_table

2. Then, connect to SECONDRY (INDNUKE-MUMBAI) and try selecting the rows. This will work!!

 select_on_secondry

Step 8. Test the Failover

•To FAILOVER, follow below steps

Before FAILOVER

 force_failover

After FAILOVER – server roles will change

after_failover

 Conclusion,

AlwaysON by design looks similar to database mirroring, but is actually a combination of both databases mirroring and clustering. The goal is to maximize the database availability and also give benefits of disaster recovery. And we term this – AlwaysON!!!!

Varun Dhawan
Support Engineer ,Microsoft SQL Server Support

Reviewed by

Balmukund Lakhani, Nikesh Mhatre
Tejas Shah, Amit Banerjee (SQL Server Escalation Services)

Leave a Comment
  • Please add 8 and 4 and type the answer here:
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  • What do you mean "Yes, you’ve heard it right. AlwaysON is NOT a clustered SQL Server Instance. As such a standalone SQL Server setup is required on both the clustered nodes."  The BOL for Denali CTP1 say that you can either use a clustered instance or a standalone instance.  Why would you want to use two standalone SQL Server instances on 2 nodes in the same cluster?  What would happen when there is a failover event within the cluster?

  • Hi Heather,

    Thanks for pointing this out. Seems we missed it at first place....so here’s the updated details:

    1. For configuring AlwaysON, we can we can either use a failover cluster instances or stand-alone instances.

    2. The "Two" standalone instances mentioned in this post are just an example for an easier demonstration.

    So assuming there are 2 standalone instances running on Windows Server Failover Clustering. In the event of cluster failover, there will be a failover from Primary to Secondary replica.

    Regards,

    Varun

  • Hello Varun

    To force FAILOVER do you click on the secondary server? Why not on the primary server?

  • Hi Varun,

    I've seen it suggested (www.brentozar.com/.../sql-server-denali-database-mirroring-rocks) that you'll be able to run your backup from a replica.  Do you know anything more about how this works? - for eg, would BACKUP LOG on the secondary replica cause the log file on the primary to be appropriately truncated?

    Thanks,

    Colin.

  • Hello Varun,

    Thanks for a very informative post on AlwaysOn. The setup screen shots are really helpful in understanding the HARD setup.

    - Pawan | SQL Server DBA

  • Hello Colin

    First apologies for a late reply as I've been busy leveling some new assignments.

    Answer to your questions is YES, it’s possible to take LOG backups on a secondary replica in an AlwaysOn (HADR) configuration. A ‘BACKUP LOG’ T-SQL will work as usual on secondary replica/s and all such log backups WILL TRUNCATE T-LOG file on primary.

    Hope this answers your query.

    Varun

  • Hi Uri

    A force causes the secondary replica to which the availability group was failed over becomes the new primary replica. This seems purely a by-design thing that such force failover is initiated from a secondary replica of the availability group.

    Varun

  • Hi Bala,

    Thanks for the innovative information . could you please describe to us to take the backup on secondary replica.Thanks

  • As you know, I am documenting my experience at the Tech Ed 2011 (India) held from March 23-25, 2011 at

  • Hi,

    Is it possible to create alwayson for database in an instance in 3 node cluster with standalone as sceondary server

  • JunDba,

    All machine participating in AlwaysOn MUST be part of same windows cluster.

  • can uable to change group ID of availabilty group

  • @Riya

    Why do you need to change the ID (which is a 'metadata') of an Availability Group?

  • It will not work on SQL Failover Cluster, Only Windows Failover Cluster is required and both the node should have same drive later.

  • Thanks for the post.

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