A Closer Look at Distributed Availability Groups. Allan Hirt, Managing Partner, SQLHA LLC Moderated By: George Carlisle

Transcription

1 A Closer Look at Distributed Availability Groups Allan Hirt, Managing Partner, SQLHA LLC Moderated By: George Carlisle

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5 BIO Allan Hirt Dual Microsoft MVP Cloud and Datacenter Management Data Platform Managing Partner & Founder, SQLHA Consultant and trainer Specialization: mission critical SQL Server High availability, disaster recovery, consolidation, virtualization, administration Based in Boston, MA Currently finishing the book Mission Critical SQL com/in/allanhirt

6 6 Quick Recap of Availability Groups Database level protection Need to account for everything outside of the DB(s) in the AG Synchronous or asynchronous data movement Up to 9 secondary replicas (2014+) Secondary replicas can be used for other things like read only workloads Requires an underlying Windows Server Failover Cluster (WSFC) All nodes participating in the AG part of the same WSFC Requires AD DS through SQL Server 2014 SQL Server 2016 supports a configuration with no AD DS * No shared storage requirement like FCIs (unless they are involved)

7 7 SQL Server 2012/2014 AG Challenges WSFC configuration with multi-site architectures Quorum Voting? Witness? AD DS/DNS situation? Copying and restoring VLDBs on secondary replicas Changing/migrating to another version of Windows Server

8 8 Distributed Availability Groups Spans multiple WSFCs and AGs Independent AG configuration in each WSFC Distributed AG = AG of AGs WSFCs can be different versions of Windows Server Underlying AGs require a Listener Used for Endpoints listener_url parameter of ALTER/CREATE AVAILABILITY GROUP Primary Primary for data movement Still only one read/write copy of the data Other primary replica distributes data to secondary replica(s) and is in a loading state

9 9 Supporting Features Ability to create an AG that does not require AD DS Windows Server SQL Server 2016 only Can mix AD DS + non-ad DS as well Direct seeding for secondary replicas No longer need to do a backup/copy/restore of the full database with files Uses the log stream Not required, but recommended

10 10 Creation Process 1. Create the individual AGs is_distributed column of sys.availability_groups Subtle difference in syntax for second AG (FOR REPLICA, not FOR DATABASE xxx REPLICA) 2. Create the distributed AG on the primary WSFC 3. Join the other AG to the distributed AG

11 11 Gotchas Enterprise Edition, T-SQL only Cannot see configuration in the WSFC is_distributed column of sys.availability_groups Only visible to individual AG primary replicas Cannot add a Listener of Listeners Chaining latency Only manual failover supported Same database, drive configuration (same as a regular AG)

12 12 Summary Distributed AGs are not for every AG deployment Distributed AGs add complexity Will make migration/upgrades easier Watch out if using synchronous everywhere If you are anti-listener, distributed AGs won t work for you

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