Architecting Availability Groups An analysis of Microsoft SQL Server Always-On Availability Group architectures 1

Derik  Database Administrator (Traditional/Operational/Production)  Spent a year pretending to be a.NET developer then back to being a DBA  Specialize in High-Availability, Disaster Recovery, and Maintenance Automation  Rebuilt the Hampton Roads SQL Server User Group in Virginia Beach, VA before moving.  Chapter leader of FairfieldPASS in Stamford, CT.  BS in Computer Information Systems with a focus in Database Management  Querying Microsoft SQL Server 2012 Databases (70-461)  Administering Microsoft SQL Server 2012 Databases (70-462) 2

Goals  Skill level: , assuming some familiarity  Not a “how to”, but there are demos  Architecture: Stand-alone instances  Architecture: Stand-alones with multiple subnets  Architecture: AG with Failover Cluster Instances  Architecture: Hybrid approach (DR on the cheap)  Back-up off-loading  Read-only routing 3

Materials Slide deck and demo queries available at: This material has already been posted. When I update the material, the most recent updates will be available. This slide will be shown again at the end of the session. 4

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Benefits of Availability Groups  When should you use them?  Automatic failover between local replicas.  DB Mirroring (soon to be ‘Basic HA’) and FCIs have the same capability.  Manual failover between DR sites.  Replication, log shipping, and DB mirroring have the same capability.  Group databases together and failover separately from other groups.  Off-load backups  Off-load read loads. 6

Stand-alone instances 7

Stand-alone instances (cont.)  Database level automatic fail-over available with synchronous commit.  Data duplication - a complete set of drives and data per replica.  Must synchronize server objects between nodes manually. 8 The beauty of this architecture is everything that it is not.

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Stand-alone instances – multi-subnet 10

Stand-alone instances – multi-subnet (cont.) 11 Nodes synchronize from the primary, remote nodes don’t speak to each other. Even more data duplication. One of the few reasons that I might consider favoring a hybrid with FCIs. Availability Group Listener handles multiple IPs across multiple subnets. Asynchronous Commit recommended for remote site, which only supports manual failover.

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AG with Failover Cluster Instances 13 Subnet 1 Subnet 2

AG with Failover Cluster Instances (cont.)  No need to synchronize server objects within subnet.  Still need to across the subnets.  Instance level failovers within subnets.  Shared storage can’t cross subnets.  Shared storage dependency.  Can’t ever have one AG replica reside on the same node as another.  Forces you to have more nodes to your cluster.  Configurations where all nodes are active are no longer as possible.  Can’t group DBs for failover, entire instance moves. 14

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Hybrid Architecture AKA DR on the cheap 16 Subnet 1 Subnet 2

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Quorum  Prevents “split-brain”  Node majority is typical  Potential voters include  Servers (physical or virtual)  File shares  Remote shared disks  Weight your votes for a complete drop of your connection to your disaster recovery site 18

Why you need to use Windows Server 2012 R2 and above 19 Quorum Demo  Dynamic Quorum  Dynamic Witness  Tie breaker

Why use the Listener?  Read-only routing.  It is capable of faster failovers.  Your applications do not have to wait for DNS time to live to expire.  One virtual network name (VNN), regardless of where the Availability Group (AG) lives.  Configuration files between DR sites can be identical.  Different VNN for each AG on the cluster.  Allows for groups of databases to failover to different servers.  No instance names to worry about. 20

Limitations of the listener bells & whistles  ApplicationIntent and MultiSubnetFailover requires.NET 4.0.  Or, 3.5 SP1 with hotfix KB   Or, JDBC 4.0  Not available for OLEDB or ODBC connections (expect in SQL Native Client some restrictions apply).  Connections must specify a database in the Availability Group in order to perform read-only routing.  Changing database context after connection has been established won’t cut it. 21

Listener Demos  SQL Server Management Studio  Persist parameters – Supposedly fixed in vNext as per MS Connect.  Not fixed for SQL Server 2016 CTP2  Reference the workarounds - parameters-in-sql-server-management-studio/ parameters-in-sql-server-management-studio/  SQLCMD.exe  SQLPS module’s Invoke-SqlCmd (Not a demo, hard to show the non- existence of something)  Add MultiSubnetFailover and ApplicationIntent options – Vote up on MS Connect! 22

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Read-only routing  Manually configured and optional.  Must connect using an Availability Group database context.  Common stumbling point, thus the 2-slide emphasis.  No SSMS wizard for configuration.  Incurs a round-robin connection performance hit. 24

Read-only routing connection flow 25 Step 1: Client connects using ApplicationIntent=ReadOnly Step 2: Primary replica replies with IP for redirection Step 3: Connection is made with read-only instance

Read-only Routing Demos  Configure - T-SQL  (Non-demo reference) AlwaysOn Tools - Denny Cherry and Associates - you/alwayson-tools you/alwayson-tools  Verify - Dynamic Management Views 26

Read-only Routing Demos  Configure - T-SQL  (Non-demo reference) AlwaysOn Tools - Denny Cherry and Associates - you/alwayson-tools you/alwayson-tools  Verify - Dynamic Management Views 27

Back-up Off-loading  Transaction log backups  COPY_ONLY full backups  Differentials cannot be taken  Various preferred replica configurations available  sys.fn_hadr_backup_is_preferred_replica 28

Availability Group Monitoring Demos  Availability Group Dashboards  Availability Group state DMVs 29

References of interest  Syncing server objects between sites   PowerShell driven desired state Availability Group failover test   SSMS AG Listener connection work around  management-studio/ management-studio/  Lazy log truncation and filestream  availability-groups/ availability-groups/  Step-by-step work through of the AG + FCI architecture 

Materials Slide deck and demo queries available at: This material has already been posted. When I update the material, the most recent updates will be available. 31 My Contact