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There was some unanswered questions about the difference between "Windows Server Failover Clustering" and "Always On Failover Cluster Instance".

From MS document:

A Windows Server Failover Clustering (WSFC) cluster is a group of independent servers that work together to increase the availability of applications and services. SQL Server 2017 takes advantage of WSFC services and capabilities to support Always On availability groups and SQL Server Failover Cluster Instances.

So we have 3 terms

  1. Windows Server Failover Clustering

  2. Always On availability groups

  3. SQL Server Failover Cluster Instances

Does that mean i have to combine 1 with 2 or 3? Or i can only use 1 only?

Because in my case (2 EC2 instance with SQL Server 2016 Standard), here's what i did

  • On first EC2, i installed Failover Clustering Manager role from Server Manager

  • Then i created cluster and add nodes

  • I did some other configurations including DNS, network, witness

  • Now when one node go off (by stop EC2), the other node go online

  • In SQL Management, i just configured Merge Replication between 2 SQL Server insides 2 EC2

In this case, i used only WSFC? The reason why i asked is because in FCI document, it stated:

Storage Contrary to the availability group, an FCI must use shared storage between all nodes of the FCI for database and log storage. The shared storage can be in the form of WSFC cluster disks, disks on a SAN, Storage Spaces Direct (S2D), or file shares on an SMB. This way, all nodes in the FCI have the same view of instance data whenever a failover occurs. This does mean, however, that the shared storage has the potential of being the single point of failure, and FCI depends on the underlying storage solution to ensure data protection.

But i noticed that i didn't have any shared storage.

@The "Are “Always On Failover Cluster Instances” and “SQL Server Failover Clustering” the same thing?" didn't explain it.

  • I read that one many times but didn't fully understand. My question was a little different? Combine 1 vs 3 is OK? – The One Dec 15 '17 at 7:18
  • Windows Server Failover Clustering (1.) is the basis for either Always On Availability Groups (2.) or Always On Failover Clustering Instances (3.). You need 1. as a prerequisite to build the other two options. Your other two options can then be either 2. or 3. or then both of them together. This results in the following options: 1. + 2. or 1. + 3. or then a combination of 1. + 2. + 3.. – John aka hot2use Dec 15 '17 at 13:45
  • @TheOne Yes. Always On Failover Cluster Instances and SQL Server Failover Clustering are the same. Note that when you use AGs, you need to install Windows Clustering feature (this is required). You can have AGs in a shared storage (FCI) or local storage (standalone SQL instance). Merge Replication is another HADR feature, you don't need WSFC or FCI for that. If you want db1 talking to db2 using Merge Replication in EC2 you can just setup standalone server for that (for simplicity sake). The Merge Replication is a nice feature in SQL but it is very tough to troubleshoot. – user37701 Dec 16 '17 at 4:19