Always On FCI vs Always On Availability Groups

Question

What is the advantage of Always On Failover Clustering vs Always On Availability Groups?

Basic Always On Failover Clustering provides server level protection, (eg: 2 servers with 1 shared disk space; if server fails, it can utilize another server on the shared disk space).

Always On Availability Groups provides both disk storage DR and server-level HA Protection. It provides 2 servers with 2 shared space.

So what benefit functionally does Always On Failover Clustering have over Availability Groups? Looking at the chart comparison I see none. Seems Availability Groups is better.

We utilize SQL Server 2016 Enterprise. Thanks.

Reviewed documentation:

• Failover Clustering and Always On Availability Groups
• SQL AlwaysOn

Answer 1

What is the advantage of Always On Failover Clustering vs Always On Availability Groups?

The main advantages given 2012->2017 for an FCI is:

1. No instance level metadata or objects required to be synchronized
2. Databases can be in any recovery model
3. Only one copy of the databases is required (1x total disk space required)
4. Generally easier to troubleshoot as it isn't a distributed system

Seems Availability Groups is better, Looking at the chart comparison I see none

It depends on what you're protecting against and what infrastructure you have in order to protect it. Then it comes down to what people have the most experience supporting.

In Availability Groups, here are some common disadvantages:

1. Instance level metadata needs to be manually synchronized between participating nodes (Logins, Jobs, certain encryption keys, proxy accounts, etc.)
2. It's a distributed system and is generally harder to troubleshoot
3. Requires your networking be of the utmost quality and lowest latency (even in asynchronous mode)
4. Requires x*n amount of storage where n is the number of replicas in the availability group and x is the sum total of size for the participating databases.