SQL Server 2012 High Availability and DR Options
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As presented to the Philadelphia SQL Server Users Group on 12/07/2012
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SQL Server 2012 High Availability and DR Options
- 1. SQL Server 2012 High Availability and DR Philadelphia SQL Server User’s Group 07-December-2011
- 2. About Me @jdanton on Twitter Joedantoni.wordpress.com Videos and Blogs at SSWUG.org Vice President of the Philadelphia SQL Server UG
- 3. Speaker Rate This is a new talk for me—I’d love feedback http://spkr8.com/s/19509
- 4. Agenda SQL Server 2008 to 2012—What’s Changed in HA and DR Geo-Clustering All about Availability Groups
- 5. Learning Objectives SQLServer HA and DR What involved in SQL Clustering How it works What’s new in 2012 HA/DR This presentation is geared towards DBAs—so feel free to stop at any time with questions
- 6. Licensing (What’s changed) The Availability Group features will require the Enterprise Edition of SQL Server The licensing model for SQL Enterprise Edition has changed. Consult your friendly Microsoft sales representative for more details Mirroring is listed as being deprecated from Standard Edition. Will still be there in 2012
- 7. Windows Core Support No GUI version of Windows Allows for fewer patches Uses PowerShell and MMCs for support
- 8. SQL Server 2012 Extended Events are used much more heavily Slipstream Install no longer required—SQL will check for updates from your Windows Update source Can use internet Windows Update or internal source
- 9. High Availability and DR Options in SQL 2008 SQL Server Clustering SQL Server Mirroring Peer to Peer Replication SQL Server Log Shipping*
- 10. HA and DR Options in SQL Server 2012 Backup and Recovery Mirroring Availability Groups (2012) Log Shipping Replication SAN Replication* Virtualization*
- 11. Clustering--2008 SQLClustering required 1 subnet to be used across the whole cluster 10.10.100.10 Cluster failover is controlled by isAlive/looksAlive processes, which check the SQL service and run @@servername
- 12. What’s new in SQL Server 2012 HA/DR New Term: Witness Disk Can be physical (SAN) disk, or cluster file share Multi-subnet clustering is supported Requires SAN replication FlexibleFailover The BIG one—Always On Availability Groups
- 13. Clustering 2012 Fullsupport for geo-distributed clusters Flexible failover model TempDB on Non-shared Disk Resource Makes PCI-based Solid State Drive an option No check for this as of CTP3—instance won’t start if TempDB drive location not available
- 14. Geo-Distributed Clustering Requires SAN replication ($$$$) Two of everything Requires really fast network connection Requires some trickery at the network/DNS level for connectivity
- 16. Flexible Failover Replaces looksAlive/isAlive functionality in SQL Clusters (and is used for Availability Groups) Now runs sp_server_diagnostics Two new parameters HealthCheckTimeout (Default 60 sec/Minimum 15 sec) Failover Condition Level
- 17. Flexible Failover Policies for Clusters Level Condition Description No automatic failover • Indicates that no failover or restart will be triggered 0 or restart automatically on any failure conditions. Failover or restart on 1 • SQL Server service is down. server down • SQL Server instance is not responsive (Resource DLL cannot Failover or restart on 2 receive data from sp_server_diagnostics within the server unresponsive HealthCheckTimeout settings). Failover or restart on • System stored procedure sp_server_diagnostics returns 3 (Default) critical server errors ‘system error’. (Critical errors > 20) Failover or restart on • System stored procedure sp_server_diagnostics returns 4 moderate server errors ‘resource error’. (Moderate errors > 17) Failover or restart on • System stored procedure sp_server_diagnostics returns 5 any qualified failure ‘query_processing error’. (Deadlock) conditions
- 18. Understanding Quorum There are a few slides on this topic, it’s a little confusing In a nutshell, you cluster has to be able to talk to itself to keep the cluster service up in running This applies to both SQL Server Failover Cluster Instances and AlwaysOn Availability Groups
- 19. Quorum Quorum is critical—contains master copy of the cluster’s configuration Serves as a tiebreaker if network communications between cluster nodes fail If Quorum fails—cluster is shut down until it’s restored
- 20. Quorum Models Node and Disk Majority (Default) Node Majority No Majority (Quorum Disk Only) Node and File Share Majority (Good for Geo Clusters)
- 21. Quorum Failure Tolerance Number of Nodes 2 3 4 5 6 7 Node Majority 0 1 1 2 2 3 Node and Disk/File Share Majority 1 2 2 3 3 4 • Assuming Disk is Up Calculation is: Cluster Up = RoundUp(Total # of Nodes/2) • Assuming Disk is Down Calculation is: ClusterUp = RoundUp (Total # of Nodes/2)-1
- 22. DR in SQL 2008 Mirroring Allowed automatic failover, but only one target Mirror target is unreadable Log Shipping Allowed multiple targets, but failover a manual process, requiring a connection string change Replication
- 25. AlwaysOn Requirements Windows Enterprise (Clustering is a requirement) SQL Server Enterprise Edition Windows Cluster No shared storage is required Quorum Disk Preferred
- 26. Flexible AG Failover Similar to how a failover clustered instance fails over Connects to instance every 30 seconds to perform health check Also, similar quorum model to Windows Failover Clustering
- 27. Allows for SAN Less HA/DR Thisisn’t a huge thing for SQL Server at big shops It may allow us to incorporate a level of DR into a virtual environment
- 28. Failover Modes Automatic failover Planned manual failover (without data loss) Forced manual failover (with possible data loss)
- 29. Failover Synchronous- Synchronous- Asynchronous- commit mode commit mode commit mode with manual- with automatic- failover mode failover mode Automatic No No Yes failover Manual failover No Yes Yes Forced failover Yes Yes No
- 30. Client Connections in This Model Availability Group Listener (Yes, SQL Server now has a listener) Works just like a failover clustering instance (single instance, single IP) Creates a VCO (AD Virtual Computer Object)
- 31. Contained Databases Isolate Database from Instance Currently only fully supported with SQL Logins No numbered procedures Eases database movement Allows for ease of migration to Azure Not quite baked out as of RC0
- 32. Read Only Replicas Can have up to 3 SQL Client 2012 will allow for this routing specifically Can take backups from read-only copys* Copy Only Backups (only full copy, does not affect primary log) Indexingmust be same on replicas Bad queries can affect status of replica
- 33. Considerations for Availability Groups All SQL servers (including the secondary in the DR site) in the same Windows domain All the databases must be in FULL recovery model The unit of failover (for local HA, as well as DR) is at the AG level, i.e., group of databases – not the instance Consider using Contained Database for containing logins for failover For jobs and other objects outside the database, simple customization needed No delayed apply on the secondary Removing log shipping means the regular log backup job is removed Need to re-establish periodic log backup (essential for truncating the log) New tools for monitoring and alerting AlwaysOn Dashboard System Center Operations Manager
- 35. Summary Lotsof Change in the HA/DR Space Licensing also changes—talk to your MS rep SQL Server Failover Clusters still a good HA option AlwaysOn Availability Groups add a lot more flexibility to DR
- 36. Contact Info @jdanton jdanton1@yahoo.com http://spkr8.com/s/19509
Editor's Notes
- Extended Events came out in SQL Server 2008, but very few people, myself included, paid much attention. Those who did found the implementation awkward and confusing. Only a few people persevered enough to discover just how powerful and amazing these things are. Which is why most anyone who wants to learn about extended events should plan on starting at one place, Jonathan Kehayias’ blog. Yeah, the Books Online help get you started, but Jonathan really makes it all take off.
- SQL Server clustering is the most obvious high availability solution that everyone knows about. However, mirroring between two SQL Servers (with a witness server) can also provide a level a both h/a and D/R. The other two options are a little bit more controversial and more complicated to setup. Both peer to peer replication and SQL Log Shipping can provide some measure of H/A, but there are caveats to this, and some data loss is possible. This is a little outside of the scope of this preso, so if you would like to know more detail around these topics, I highly recommend Paul Randal’s white paper on SQL HA and DR options. I’ll provide a link at the end of this presentation.
- DR Options—yes backup and recovery is your first line of defense in the event of a disaster. You should have extensive monitoring and notification around your backup process, and take regular transaction log backups, if you need point in time recovery.Mirroring is probably the best high availability option. With a witness server (a server that sits in between the two mirrors) you get automatic failover in the event of the failure of your primary instance goes down. Most applications that use Microsoft connections to your database can support mirroring. The only negative, is that unless you have enterprise edition, you are limited to synchronous mirroring, which can have a performance impact on your primary. Enterprise edition brings in asynchronous mirroring, which allows for greater flexibility and distance between sites with no performance impact.Log shipping and Replication—both of these will require manual intervention in the event of a failure. However, they are very mature technologies and can work over great distances. This is not a DR scenario, but I have an application which replicates from the US to Switzerland over a nominal network connection, running on SQL 2000, and I haven’t had to touch it in two years. (Knocks on wood).Lastly SAN replication—this is really cool technology, and can enable the concept of geo-distributed clusters (also covered in Paul’s white paper). This is pretty far out of scope for today’s presentation, but I’ll say this—while really cool, it’s really complex to setup, and really expensive. You need additional software from your SAN vendor, which is always pretty pricey, and the additional network bandwidth to transfer bits in real time over the network. When I was at Wyeth, we did this between Philadelphia and Pearl River NY for the SAP system that ran the business. But the cost made it prohibitive to do much else. Also, when it goes wrong, it can be ugly.
- Automatic failoverAutomatic failover is supported only when the current primary and one secondary replica are both configured with failover mode set to AUTOMATIC and the secondary replica currently synchronized. If the failover mode of either the primary or secondary replica is MANUAL, automatic failover cannot occur. Occurs only between a primary replica and a secondary replica that are configured for synchronous-commit mode and automatic failover mode when the secondary replica is in the SYNCHRONIZED state.Planned manual failover (without data loss)Planned manual failover, or manual failover, is useful for administrative purposes. It is supported only if both the primary replica and secondary replica are configured for synchronous-commit mode and the secondary replica is currently synchronized (in the SYNCHRONIZED state). A database administrator manually initiates a manual failover.Forced manual failover (with possible data loss)Intended only for disaster recovery, forced manual failover, or forced failover, is supported only when the synchronization health of the target availability replica either NOT_SYNCHRONIZING or SYNCHRONIZING. This is the only form of failover supported by in asynchronous-commit availability mode.Automatic failover setExists only when a pair of availability replicas (including the current primary replica) are configured for synchronous-commit mode with automatic failover, if any. An automatic failover set takes effect only if the secondary replica is currently SYNCHRONIZED with the primary replica. Synchronous-commit failover setExists only when a set of two or three availability replicas (including the current primary replica) are configured for synchronous-commit mode. A synchronous-commit failover set takes effect only if the secondary replicas are configured for manual failover mode and at least one secondary replica is currently SYNCHRONIZED with the primary replica. Entire failover setWithin a given availability group, the set of all availability replicas whose operational state is currently ONLINE, regardless of availability mode and of failover mode. The entire failover set becomes relevant when no secondary replica is currently SYNCHRONIZED with the primary replica.
- The amount of time that the database will be unavailable during a failover depends on the type of failover and its cause. For more information, see Estimate the Interruption of Service During Failover of an Availability Group (SQL Server). ImportantTo support client connections after failover, except for contained databases, logins and jobs defined on any of the former primary databases must be manually recreated on the new primary database. For more information, see Management of Logins and Jobs for the Databases of an Availability Group (SQL Server).
- A partially contained database is a contained database that allows the use of uncontained features. Partially contained databases do not allow the following actions or entities. Numbered proceduresSchema-bound objects that depend on built-in functions with collation changesBinding change resulting from collation changes, including references to objects, columns, symbols, or types.Replication, change data capture, and change tracking.Use the sys.dm_db_uncontained_entities and sys.sql_modules (Transact-SQL) view to return information about uncontained objects or features. By determining the containment status of the elements of your applications, you can discover what objects or features need to be replaced or altered for use in a fully contained database.