Architecting Availability Groups An analysis of Microsoft SQL Server Always-On Availability Group architectures 1 Derik Hammer @sqlhammer derik@sqlhammer.com www.sqlhammer.com 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: 200-300, 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: http://www.sqlhammer.com/blog/community/ 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 5 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 Server Server Availability Replica A Availability Replica B Local Disk(s) Local Disk(s) 7 Stand-alone instances (cont.) Server Server Availability Replica A Availability Replica B Local Disk(s) 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. Local Disk(s) The beauty of this architecture is everything that it is not. 8 9 Stand-alone instances – multi-subnet Server Server Availability Replica C Subnet 2 Availability Replica D Local Disk(s) Local Disk(s) Server Server Subnet 1 Availability Replica A Local Disk(s) Availability Replica B Local Disk(s) 10 Stand-alone instances – multi-subnet (cont.) • 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. 11 12 AG with Failover Cluster Instances Subnet 1 Shared Disks Server Server Server Availability Replica B Server Availability Replica A Subnet 2 Shared Disks 13 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 15 Hybrid Architecture AKA DR on the cheap Subnet 2 Subnet 1 Server Shared Disks Server Server Availability Replica B Availability Replica A Local Disks 16 17 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 Quorum Demo Why you need to use Windows Server 2012 R2 and above Dynamic Quorum Dynamic Witness Tie breaker 19 Why use the Listener? Read-only routing. It is capable of faster failovers. 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. Your applications do not have to wait for DNS time to live to expire. 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 KB2654347. https://support.microsoft.com/en-us/kb/2654347 Or, JDBC 4.0 Not available for OLEDB or ODBC connections (expect in SQL Native Client 2012+ 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. http://bit.ly/1wKPucP Not fixed for SQL Server 2016 CTP2 Reference the workarounds http://www.sqlhammer.com/blog/store-optional-connectionparameters-in-sql-server-management-studio/ SQLCMD.exe SQLPS module’s Invoke-SqlCmd (Not a demo, hard to show the nonexistence of something) Add MultiSubnetFailover and ApplicationIntent options – Vote up on MS Connect! http://bit.ly/1BCbB82 22 23 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 Step 1: Client connects using ApplicationIntent=ReadOnly Step 2: Primary replica replies with IP for redirection Primary Replica (Includes Listener) Client Step 3: Connection is made with read-only instance Secondary Replica (Read-Only) 25 Read-only Routing Demos Configure - T-SQL (Non-demo reference) AlwaysOn Tools - Denny Cherry and Associates http://dcac.co/applications/hosted-byyou/alwayson-tools Verify - Dynamic Management Views 26 Read-only Routing Demos Configure - T-SQL (Non-demo reference) AlwaysOn Tools - Denny Cherry and Associates http://dcac.co/applications/hosted-byyou/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 http://www.sqlhammer.com/blog/store-optional-connection-parameters-in-sql-servermanagement-studio/ Lazy log truncation and filestream http://www.sqlhammer.com/blog/failing-over-alwayson-availability-groups/ SSMS AG Listener connection work around http://www.sqlhammer.com/blog/synchronizing-server-objects-for-availability-groups/ http://www.sqlhammer.com/blog/filestream-garbage-collection-with-alwaysonavailability-groups/ Step-by-step work through of the AG + FCI architecture http://www.sqlhammer.com/blog/how-to-configure-sql-server-2012-alwayson-part-1-of-7/ 30 Materials Slide deck and demo queries available at: http://www.sqlhammer.com/blog/community/ This material has already been posted. When I update the material, the most recent updates will be available. My Contact Information: @SQLHammer 31 derik@sqlhammer.com www.sqlhammer.com
