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

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.

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

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

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

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

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.

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.

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.

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

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

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

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.

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

SQL 2016 AlwaysOn Demo Setup VM1 VM2 VM3 VM4 Host Name SQLDC SACTO1 SACTO2 NEWYORK1 OS W2k16 Server W2K16 Server IP Address 192.168.60.1 192.168.60.2 192.168.60.3 192.168.60.4 Subnet Mask 255.255.255.0 Domain: SQLDemos.local Cluster Name: DemoCluster(192.168.60.5) Availability Group: DemoAG Listener: DemoListener – 192.168.60.10

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

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

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

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

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.

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

Distributed Availability Group in SQL 2016

Questions?