1. High Availability/Disaster Recovery Solution
SQL 2016 AOAG’s
High Availability/Disaster Recovery Solution

2. Why do we need another solution?
The current High Availability and Disaster Recovery Solutions from Microsoft are scattered.
High Availability / Disaster Recovery Solutions:
Windows Failover Clustering (WSFC)
Database Mirroring (DBM)
Log Shipping
Database Replication is not a viable HA/DR solution.

3. SQL Failover Clustering (WSFC)
A failover cluster is a combination of two or more servers(nodes) connected to a shared storage.
Active
Node 1
Windows Cluster
Active
client
DataFiles
Shared Storage
App Server
Basic Functionality of a WSFC
Node 2

4. SQL Failover Clustering (WSFC) cont.
Active
Node 1
Windows Cluster
Active
client
DataFiles
Shared Storage
App Server
Node 2

5. SQL Failover Clustering Issues
Protects against hardware loss and not disk loss.
Passive node is not used thus not achieving maximum utilization of resources.
Can not read data/backup/etc from Non-Active node

6. Database Mirroring Primary DB Primary SQL Server Client App Server
Mirrored SQL Server
Mirrored DB
Primary DB

7. Database Mirroring Issues
Can have only one mirror. No multiple copies of data.
Mirrored database is not readable, though snapshots can be taken from the mirrored database.
Need to be setup per database.
Per database failover, no automatic failover of multiple databases.
No sql logins/jobs are replicated to the mirrored instance.
Either synchronous or asynchronous mirroring is supported but not both.

8. Log Shipping Issues Cannot have synchronized databases.
To be setup per database.
In case of failover, the connection string needs to change to point it to the failover server.
No logins/jobs are replicated to the mirrored instance.

9. What if we had all these features in a single solution?
Protects against hardware loss.
Protects against disk loss.
Multiple copies of replicated databases.
Readable mirrored databases thus maximizing resources.
Multiple database failover at once.
No need to change the connection string in case of failover, you can use the same abstract name.
Failover can occur across datacenters without extra effort.

10. Always On Availability Groups
Introducing…..
Always On Availability Groups

11. Modes of SQL2016 AlwaysOn
1. AlwaysOn Failover Clustering Instance(FCI). 2. AlwaysOn Availability Groups. Today we will discuss AlwaysOn Availability Groups.

12. SQL 2016 AOAG Requirements: Needs to have Windows failover cluster**.
Supported in Enterprise Edition Only (8 Nodes/2 Synchronous)
Install individual SQL servers on each machines, not cluster aware.
All servers should can be in a same/different windows cluster.**
Matching hardware not required.
Database should have Full Recovery model with at least one full successful backup.
All nodes must be in the same AD domain**.
**- Changed in SQL 2016 onwards

13. AlwaysOn Vocabulary
Availability Group (AG): A set of databases working together in a group.
Availability Replicas: A set of Mirrored databases in a availability group.
Availability Group Listener: Virtual network name.

14. Demo Architecture Local Data Center(Sacramento) DR Site SACTO1 SACTO2
Synchronous
DR Site
Client
App Server
Asynchronous
NEWYORK1

15. SQL 2016 AlwaysOn Demo Setup
VM1
VM2
VM3
VM4
Host Name
SQLDC
SACTO1
SACTO2
NEWYORK1 OS
W2k16 Server
W2K16 Server
IP Address
Subnet Mask
Domain: SQLDemos.local
Cluster Name: DemoCluster( )
Availability Group: DemoAG
Listener: DemoListener –

16. Demo Setup a Cluster Install SQL 2016. Install SSMS 17.0
Setup an AG, synchronous and asynchronous Replica.
Readable secondary
DBCC on secondary
Backup on secondary
Synchronous Failover
Asynchronous Failover
Listener
Read-only routing

17. SQL AlwaysOn Features
Combines the best features of mirroring and clustering
Can have up to 3 mirrored synchronous databases - automatic failover
Can have up to 7 mirrored asynchronous databases - manual failover
Can have read-only secondary databases
Can have one or more databases in an availability group so in case of a failover, all databases failover at once
SQL Logins can be failed over using contained databases

18. SQL AOAG features contd..
Backups can occur on the replica databases
DBCC commands can be run on secondary
Setup and Failover can be scripted using Windows PowerShell

19. Some disadvantages Needs Enterprise Edition of SQL
Needs Windows Cluster.
Need double the storage compared to WSFC as there is no shared storage.
If replica is used, you need to take care of extra licensing
System databases cannot be replicated- users(contained databases) and jobs are not part of replication
Differential backups are not supported on secondary

20. What is available for Standard Edition
Basic Availability Group(BAG)
Replaces database mirroring (Deprecated).
Only one database per BAG.
No readable secondary.
You are responsible for failing over multiple databases in case of failover.
Synchronous only.

21. Always On Availability Groups in SQL 2016
Failover can happen on database health
Distributed Transactions supported starting in SQL 2016
3 synchronous Replicas and possible failover targets.
Load balancing across readable secondary's.
Redo Rate improvement.
Distributed Availability Groups

22. Distributed Availability Group in SQL 2016

23. Questions?