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AlwaysOn AG versus FCI Licensing

  • June 24, 2019 at 3:54 pm

    #3657013

    AlwaysOn Availability Groups (AG) and AlwaysOn Failover Cluster Instances (FCI)

    Checking to see the licensing cost for 2 and 3. Would there be licensing cost for secondary replica or the cost would be for secondary server only? Please advise?

    1. FCI is for HA scenarios.
    2. An AG synchronous secondary replica, co-located with the primary, is for HA scenarios.
    3. An AG asynchronous secondary replica, in a different datacenter, is for DR scenarios.

  • June 24, 2019 at 5:27 pm

    #3657040

    There's a link to the SQL 2017 Licensing Guide at https://www.microsoft.com/en-us/sql-server/sql-server-2017-pricing

    Pages 26-29 of that guide cover HA licensing, including this line on p.27:

    For each server licensed with SQL Server 2017 and covered by active SA, customers can run up to the same number of passive failover instances in a separate, OSE to support failover events. A passive SQL Server instance is one that is not serving SQL Server data to clients or running active SQL Server workloads

    My take on your scenarios and the guide (I'm not a licensing expert, this is personal opinion only):

    1. FCI is for HA scenarios. - Each SA licensed server allows one FCI failover target, provided that target is fully passive until failover, and only if that failover moves all processing from the initial server
    2. An AG synchronous secondary replica, co-located with the primary, is for HA scenarios. - Provided that secondary replica does not allow read-only connections, an SA licensed primary will include the licenses for the secondary.
    3. An AG asynchronous secondary replica, in a different datacenter, is for DR scenarios. - Looks like SA covers the secondary, per the image on the bottom of page 28 (with a licensed Primary in Boston and a passive FCI failover target in LA that needs no additional license). The key to that appears to be that either both nodes are in the cloud, or none of them. If you split the cluster between a 1st-party DC and the cloud, you may need to license each node regardless of SA.

     

     

    Eddie Wuerch
    MCM: SQL

  • June 24, 2019 at 10:50 pm

    #3657173

    I think Eddie has it correct. Check with MS, but the general rule of thumb is that

    a) you need SA

    b) you cannot use the secondary for anything. No reads, no DBCC, nothing. If you do, this needs its own license.

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