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difference between failover clustering and aag RRS feed

  • Question

  • Hi,

    I am new to MSSQL. My question is what exactly is the difference between failover clustering and always availability group in MS SQL and replication for DR site

    Wednesday, July 24, 2013 4:42 PM

Answers

  • There are already three good answers here, let me try to sum it up and put one Thing in perspective a Little:

    The biggest differences between Availability Groups (AGs) and Clusters (FCIs) are

    1) As Uri pointed out: AGs are on DATABASE Level, FCIs are on INSTANCE Level. Meaning: Jobs, Logins, etc. are automatically "in sync" in FCIs, but not in AGs. (As they reside in the Master and MSDB databases...)

    2) FCIs Need shared storage of some sort. This can either be a SAN or an SMB share. AGs actually Keep multiple copies of the same data on different discs, ensuring consistency on a program Level. (MEaning: SQL Server does it, rather than relying on the storage below...)

    3) AGs are an Enterprise Edition Feature, while FCIs (at least in a reduced featureset) can be used with Standard Edition.

    Regarding DR Scenarios: The Suggestion was made that AGs are mainly for DR Scenarios. That is only half true... AGs are better suited for DR Scenarios than FCIs, as for FCIs you would Need to implement storage replication, which is cost intensive and somewhat slow.) The other half I would not agree upon though... AGs are as well suited for high availability as FCIs are... So even in non-DR Scenarios they are a good Option. (Especially if you don't want to invest in a SAN...)

    Hope that gives you an idea..

    Rick

    Thursday, July 25, 2013 7:03 AM
  • Hi n.varun,

    Just addition to the replay above.

    SQL Server 2012 takes advantage of Windows Server Failover clustering services and capabilities to support AlwaysOn Availability Groups and SQL Server Failover Cluster Instances.

    AlwaysOn Availability Groups, is the high availability and disaster recovery solution introduced in SQL Server 2012, requires Windows Server Failover Clustering (WSFC). Also, though AlwaysOn Availability Groups is not dependent upon SQL Server Failover Clustering, you can use a failover clustering instance (FCI) to host an availability replica for an availability group.

    An FCI can leverage AlwaysOn Availability Groups to provide remote disaster recovery at the database level. Deploying AlwaysOn Availability Groups requires a Windows Server Failover Clustering (WSFC) cluster. To be enabled for AlwaysOn Availability Groups, an instance of SQL Server must reside on a WSFC node, and the WSFC cluster and node must be online.

    For more information please referring following links:

    Overview of AlwaysOn Availability Groups (SQL Server)
    http://msdn.microsoft.com/en-us/library/ff877884.aspx
    Failover Clustering and AlwaysOn Availability Groups (SQL Server)
    http://msdn.microsoft.com/en-us/library/ff929171.aspx
    AlwaysOn Failover Cluster Instances (SQL Server)
    http://msdn.microsoft.com/en-us/library/ms189134.aspx
    Window Server Failover Clustering (WSFC) with SQL Server
    http://msdn.microsoft.com/en-us/library/hh270278.aspx

    If you have any questions, please feel free to ask.
    Regards,
    Nicole Yu


    Nicole Yu
    TechNet Community Support


    • Edited by Nicole Yu Thursday, July 25, 2013 5:20 AM miss a link
    • Proposed as answer by PrinceLucifer Thursday, July 25, 2013 6:56 AM
    • Marked as answer by Fanny LiuModerator Wednesday, July 31, 2013 1:08 PM
    Thursday, July 25, 2013 5:17 AM
  • In addition

    FCI (Clustering) = protection on the server/instance level

    Always ON AG = protection on the database/s level

    BTW, AG is supported on with Enterprise Edition.


    Best Regards,Uri Dimant SQL Server MVP, http://sqlblog.com/blogs/uri_dimant/

    MS SQL optimization: MS SQL Development and Optimization
    MS SQL Blog: Large scale of database and data cleansing
    Remote DBA Services: Improves MS SQL Database Performance

    Thursday, July 25, 2013 5:25 AM
  • Hello,

    Failover Cluster is a technique for High Availability. the most frequent FC scenario can have multiple servers acting as cluster nodes. those nodes are connected to shared drivers (i.e SAN) so One node owns all the services (The active node) and the others are on hold in case the have to quickly become active.

    AlwaysOn is a SQL solution for Disaster Recovery which requires the Windows Cluster layer installed on every node

    Failover Cluster

    http://msdn.microsoft.com/en-us/library/hh270278.aspx 

    AlwaysOn

    http://msdn.microsoft.com/en-us/library/ff929171.aspx

    Regards


    Javier Villegas | @javier_villhttp://sql-javier-villegas.blogspot.com/

    Please click "Propose As Answer" if a post solves your problem or "Vote As Helpful" if a post has been useful to you

    Wednesday, July 24, 2013 6:20 PM

All replies

  • Hello,

    Failover Cluster is a technique for High Availability. the most frequent FC scenario can have multiple servers acting as cluster nodes. those nodes are connected to shared drivers (i.e SAN) so One node owns all the services (The active node) and the others are on hold in case the have to quickly become active.

    AlwaysOn is a SQL solution for Disaster Recovery which requires the Windows Cluster layer installed on every node

    Failover Cluster

    http://msdn.microsoft.com/en-us/library/hh270278.aspx 

    AlwaysOn

    http://msdn.microsoft.com/en-us/library/ff929171.aspx

    Regards


    Javier Villegas | @javier_villhttp://sql-javier-villegas.blogspot.com/

    Please click "Propose As Answer" if a post solves your problem or "Vote As Helpful" if a post has been useful to you

    Wednesday, July 24, 2013 6:20 PM
  • Hi n.varun,

    Just addition to the replay above.

    SQL Server 2012 takes advantage of Windows Server Failover clustering services and capabilities to support AlwaysOn Availability Groups and SQL Server Failover Cluster Instances.

    AlwaysOn Availability Groups, is the high availability and disaster recovery solution introduced in SQL Server 2012, requires Windows Server Failover Clustering (WSFC). Also, though AlwaysOn Availability Groups is not dependent upon SQL Server Failover Clustering, you can use a failover clustering instance (FCI) to host an availability replica for an availability group.

    An FCI can leverage AlwaysOn Availability Groups to provide remote disaster recovery at the database level. Deploying AlwaysOn Availability Groups requires a Windows Server Failover Clustering (WSFC) cluster. To be enabled for AlwaysOn Availability Groups, an instance of SQL Server must reside on a WSFC node, and the WSFC cluster and node must be online.

    For more information please referring following links:

    Overview of AlwaysOn Availability Groups (SQL Server)
    http://msdn.microsoft.com/en-us/library/ff877884.aspx
    Failover Clustering and AlwaysOn Availability Groups (SQL Server)
    http://msdn.microsoft.com/en-us/library/ff929171.aspx
    AlwaysOn Failover Cluster Instances (SQL Server)
    http://msdn.microsoft.com/en-us/library/ms189134.aspx
    Window Server Failover Clustering (WSFC) with SQL Server
    http://msdn.microsoft.com/en-us/library/hh270278.aspx

    If you have any questions, please feel free to ask.
    Regards,
    Nicole Yu


    Nicole Yu
    TechNet Community Support


    • Edited by Nicole Yu Thursday, July 25, 2013 5:20 AM miss a link
    • Proposed as answer by PrinceLucifer Thursday, July 25, 2013 6:56 AM
    • Marked as answer by Fanny LiuModerator Wednesday, July 31, 2013 1:08 PM
    Thursday, July 25, 2013 5:17 AM
  • In addition

    FCI (Clustering) = protection on the server/instance level

    Always ON AG = protection on the database/s level

    BTW, AG is supported on with Enterprise Edition.


    Best Regards,Uri Dimant SQL Server MVP, http://sqlblog.com/blogs/uri_dimant/

    MS SQL optimization: MS SQL Development and Optimization
    MS SQL Blog: Large scale of database and data cleansing
    Remote DBA Services: Improves MS SQL Database Performance

    Thursday, July 25, 2013 5:25 AM
  • There are already three good answers here, let me try to sum it up and put one Thing in perspective a Little:

    The biggest differences between Availability Groups (AGs) and Clusters (FCIs) are

    1) As Uri pointed out: AGs are on DATABASE Level, FCIs are on INSTANCE Level. Meaning: Jobs, Logins, etc. are automatically "in sync" in FCIs, but not in AGs. (As they reside in the Master and MSDB databases...)

    2) FCIs Need shared storage of some sort. This can either be a SAN or an SMB share. AGs actually Keep multiple copies of the same data on different discs, ensuring consistency on a program Level. (MEaning: SQL Server does it, rather than relying on the storage below...)

    3) AGs are an Enterprise Edition Feature, while FCIs (at least in a reduced featureset) can be used with Standard Edition.

    Regarding DR Scenarios: The Suggestion was made that AGs are mainly for DR Scenarios. That is only half true... AGs are better suited for DR Scenarios than FCIs, as for FCIs you would Need to implement storage replication, which is cost intensive and somewhat slow.) The other half I would not agree upon though... AGs are as well suited for high availability as FCIs are... So even in non-DR Scenarios they are a good Option. (Especially if you don't want to invest in a SAN...)

    Hope that gives you an idea..

    Rick

    Thursday, July 25, 2013 7:03 AM
  • ThanQ All for quick response 
    Thursday, July 25, 2013 5:46 PM
  • HI there,

    I see two different questions here. 

    1. difference between failover clustering and always availability group

    Fail over clustering is at instance level. When one instance stops working automatically fail over to second instance. That means all your clients accessing databases on the previous instance will switch automatically to the second instance.

    Where as Always availability group is at database level.  A group of databases fail over from one instance to other instance. In this case first instance may still working and have other databases.  

      2. Replication for DR site

    Replication is other high available feature; it is also at database level. You can implement this feature between two databases on different instances. You may call your instances prod, DR, DMZ etc.

    Thanks

    kumar

    Monday, July 29, 2013 2:36 AM
  • SQL Server 2016 supports in standard edition now two node AG <g class="gr_ gr_24 gr-alert gr_spell gr_run_anim gr_inline_cards ContextualSpelling ins-del" data-gr-id="24" id="24">set ups</g>. https://www.microsoft.com/en-us/sql-server/sql-server-2016-editions
    Saturday, April 8, 2017 2:56 PM