What is FCI and HA?

Question

I read some articles, but what's the difference between FCI and HA?

It is really confused, when and where to use that? Could you describe them with simple words?

Answer 1

Hi charmax001,

FCI is a switch between nodes. When one node fails, all resources come online at the other node.

AG has one primary replica and multiple secondary replicas. Data changes on the primary replica are synchronized to the secondary replica.

FCI is based on shared memory. AG are not required to bese on Shared Disk, but can also be stored on Local Disk.

When the primary replica fails, the secondary replica becomes primary.

Check it out here: https://www.starwindsoftware.com/blog/always-on-availability-groups-vs-failover-cluster

Regards，

Zoe Hui

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Answer 2

Hi charmax001

Thanks for your question.

FCI stands for Failover Cluster Instance, and HA stands for High Availability. These are two concepts related to ensuring the availability and reliability of SQL Server databases.

FCI stands for Failover Cluster Instance, which is a feature of SQL Server that provides high availability by clustering multiple servers together to act as a single instance. This means that if one server fails, another server in the cluster can take over and provide continued service.

HA stands for High Availability, which is a broader term that refers to any solution that provides continuous availability of a service or application. In the context of SQL Server, HA can be achieved through various methods, including FCI, Always On Availability Groups, and database mirroring.

Please watch the YouTube Video https://youtu.be/mN18npFVFmE  from timeline 1:23 which explain about FCI (What is Failover cluster) and also Talks about availability group from timeline 4:28.

Also sharing you the Microsoft community blog about "An overview of High Availability and Disaster Recovery solutions available for SQL Server"

https://techcommunity.microsoft.com/t5/core-infrastructure-and-security/an-overview-of-high-availability-and-disaster-recovery-solutions/ba-p/370479

Let us know if you have any additional questions on those lines.

Thank you!

Answer 3

Hey,

As mentioned, SQL FCI provides High Availability for your SQL instances. It requires multiple servers and shared storage to be configured. Check for more information: https://learn.microsoft.com/en-us/sql/sql-server/failover-clusters/windows/always-on-failover-cluster-instances-sql-server?view=sql-server-ver16

For shared storage, separate SAN or software-defined storage can be used. StarWind VSAN is a nice example of shared storage. It can replicate storage between the nodes for SQL FCI. https://www.starwindsoftware.com/starwind-virtual-san

There are also other options to achieve HA for SQL databases such as Always On Availability groups, replication, mirroring or log shipping. Might help: https://www.geeksforgeeks.org/high-availability-ha-in-sql-server/

Cheers,     
Alex Bykovskyi     
StarWind Software     
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