1. ALWAYSON AVAILABILITY GROUPS
Replicas, Listeners & Quorums, Oh My!
Kevin Howell
SQL Saturday #517
Philadelphia, June 2016

2. All about me Kevin Howell 3 Kids Cubmaster & Wrestling Coach & 1 Wife
15 Years Developer & DBA
Joined Microsoft® in March 2016
Website:
& 1 Wife

3. Agenda Basics WHY? Terminology Modes Requirements Versions Good Stuff
Environment Setup
Availability Group Setup
Failover Demo
Details, Details…
2016 Improvements
Keys to Success
Questions

4. WHY?

5. Why AGs? High Availability: Disaster Recovery:
Minimize disruption of service via hardware solution
Disaster Recovery:
Ability to reestablish services after an unplanned hardware outage
Shared Goal: Ensure Data Integrity is maintained

6. Why? Rolling Upgrades Passive Secondary Active Primary
Steps
Stop Synchronizing
Upgrade Secondary
Failover to Secondary
Upgrade Primary
Restart Synchronization
Failover to Initial Primary
Fail Over
2016
2014
2016
2014
Passive Secondary
Active Primary
Passive Secondary
Active Primary

7. Windows Server Failover Cluster
Terminology
Windows Server Failover Cluster
Instance 1
Instance 2
Window Server Failover Cluster Group of independent servers that work together to maintain availability of services
Listener
Virtual name to direct incoming database traffic to the primary replica or read-only secondary
Availability Group
Container for a set of databases that failover together
Primary Replica
Makes databases available for read/write connections and sends transaction logs to secondary replicas
Secondary Replica
Maintains a copy of availability databases. Serves as a failover target. Allows Read- Only access and Backups
Availability Group
Primary Replica
Secondary Replica
Listener

8. A STEp Further…
SQL 2016 supports 8 secondary replicas (up to 2 synchronous commit)

9. Just one more step…
Symmetrical Hardware, but not necessary

10. More terminology
Quoroum – collector of votes among nodes within the Availability Group to determine if state is healthy. Majority of votes wins
Witness (File Share or Disk) – needed in cases where there are an even number of nodes in Availability Group for tie-breaker

11. demo Quorum & Witness in Azure Lab
Windows Server VM (Failover Cluster Manager)

13. Availability group modes
Asynchronous Commit Mode:
Primary commits without waiting for secondary verification of a hardened log
Only Manual failovers are available with Asychronous
MINIMAL TRANSACTIONAL LATENCY, POSSIBLE LOSS OF DATA
Synchronous Commit Mode:
Prior to transaction commit, secondary must confirm the log has been hardened
Both Manual & Automatic failovers are available with Synchronous
COMMITTED TRANSACTIONS ARE FULLY PROTECTED, INCREASED TRANSACTAIONAL LATENCY

14. Requirements Window Server 2012 (For SQL 2016)
Windows Server 2008 (For SQL 2014 & 2012)
SQL Server Licenses
2016 Enterprise (Full Availability Groups)
2016 Standard (Basic Availability Groups)
2014 Enterprise
2012 Enterprise
Windows Server Failover Cluster

15. Availability group versions
SQL 2016 Enterprise
SQL 2016 Standard
SQL 2014
SQL 2012
Secondary Replicas 8 1 4
Synchronous Secondary Replicas 2
Automatic Failover Targets 3
N/A
AD Domain Required No
Yes
DTC Support
Group Managed Service Account
Direct Seeding of Replicas

16. Now the good stuff… DEMO
Azure Marketplace – Availability Group Cluster
Environment Setup
Availability Group Setup/Deployment
Availability Group Management
SSMS

17. SQL 2016 Improvements Log Transport Performance
Development focused on matching PCIE Class Storage
Streamlined Pipeline for Data Transport to Replicas
Load Balancing among Read-Only Secondaries
Read traffic spread across secondaries
Standard Edition Basic Availability Groups
Replacement for Database Mirroring
2 node AG (Primary + 1 Secondary), 1 Database

18. SQL 2016 Improvements
Domain Independent Availability Groups
Cross Domain/No Domain Options (think consolidation)
Database Level Failover Trigger (instead of Instance Level)
DTC Support with Availability Groups
3 Failover Available Replicas
Group Managed Service Accounts (gMSA)
Direct Seeding of Replicas (no backup onto secondaries)

19. Keys to success Plan out your topology & failover processes
Ensure infrastructure can support bandwidth for log transport
Determine your geo-replication sensitivity
Explore hybrid solution (on-prem/cloud)
Consider Read-only secondaries for your reporting purposes

20. Questions?

21. Contact information
Website:

22. Resources
group/
Availability-Groups-Enhancements
need-a-file-share-witness-or-no/
template-updated-with-internal-listeners-and-optimized-performance/