Always-on, Quorum and Direct seeding

When defining a Windows Failover Cluster to build an SQL Server Always On Availability Group over it, will we use this cluster option “Add all eligible storage to the cluster”? why?

No. We need to uncheck the Add all eligible storage to the cluster option.

This is due to the fact that Always On Availability Group feature works based on having dedicated storage for each replica without having shared storage between the replicas.

What are the quorum configuration modes that are available in Windows Failover Clustering?

• Node Majority Quorum configuration mode in the Windows Failover Cluster, with each cluster node, gives one Vote. This option fits a cluster with an odd number of nodes
• Node & Disk Majority Quorum configuration mode in the Windows Failover Cluster, with each cluster node, gives one vote, with an additional vote for the cluster quorum disk. This option fits the clusters with an even number of nodes
• Node & File Share Majority Quorum configuration mode in the Windows Failover Cluster, with each cluster node, gives one vote, with an additional vote for a shared file
• No Majority, where the status of the cluster depends completely on the availability of the Quorum disk

What is the difference between configuring the secondary replica as readable or read-intent only?

• The readable secondary allows read-only access to the secondary databases
• Read-Intent Only secondary replica allows the secondary server to serve the read-only workload ONLY, where the connection string of the application should explicitly mention the                  Application Intent=Readonly parameter

What is SQL Server Always On Availability Group Read-Only Routing List?

A new option introduced in SQL Server 2014 version, in which the read-only workload will be redirected to the first available secondary replica specified in a predefined routing list, taking into consideration that the application explicitly mentions the Application Intent=Readonly parameter.

What is the difference between the Direct Seeding and Full Backup and Log Backup initial synchronization processes in Always On Availability Group?

In the Full backup and log backup method, the initial synchronization between the primary and secondary replicas is performed by taking full and transaction log backups of the primary database to a predefined shared folder then restore it to the secondary replicas.

The Direct Seeding method, introduced in SQL Server 2016, the secondary databases will be initialized automatically using Microsoft SQL Server Virtual Device Interface (VDI) backup that is performed to the secondary replica over the network without the need for any network share.