Understanding Fail Over Clustering: 6 Important Aspects

on Clustering, Data Recovery, Data Replication, Microsoft • May 19th, 2022 • Write for Hevo

Companies which rely on online transactions can not allow server crashes as it will hamper their data records and affect their business adversely.  Therefore, such companies seek methods to develop a full proof mechanism that can keep their data safe even in the case of server crashes. Fail Over CLustring is one such mechanism.

Fail Over Clustering is a mechanism that works on a set of computer servers that collaborate to ensure either High Availability (HA) or Continuous Availability (CA) for server applications. This mechanism ensures that even if one server goes down, another cluster node can undertake its workload without causing any interruptions.

This article will introduce Fail Over Clustering and list its key features. It will further discuss the importance of this mechanism and define its various types. The article will also explain the 2 key processes involved in the working of this clustering. Read along to learn the applications and limitations of Fail Over Clustering!

Table of Contents

What is Fail Over Clustering?

Fail Over Clustering: Data Clustering Logo
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Fail Over Clustering is a mechanism that provides scalability and availability to your server workloads. Many popular server applications like Microsoft Exchange Server, Microsoft SQL Server, Hyper-V, etc. rely on the Fail Over Clustering for their data’s safekeeping. Failover Clusters are available both in the physical and virtual forms and you choose the type of cluster according to your server application’s needs. 

The key objective of Fail Over Clustering is to offer CA (Continuous Availability) or HA (Higher Availability)  services for your online running applications. The clusters that guarantee CA are also known as  FT (Fault Tolerant) clusters because they empower users to work on applications without witnessing any timeouts due to a server crash. HA clusters on the other hand can suffer from a brief service interruption. However, they will support your system to recover automatically without suffering from any data loss.

Key Features of Fail Over Clustering

The following features make Fail Over Clustering a must-have mechanism:

  • Scalability: Since Fail Over Clustering operates on a group of clusters that work together to prevent server failure, you can easily scale this mechanism by adding new clusters to the group. 
  • Stability: The Clustered Servers are known as nodes and are connected via physical cables. Now, even if one or more nodes fail due to external circumstances, the remaining nodes can provide service in place of the filed nodes using the Fail Over Clustering mechanism.
  • Real-time Monitoring: The Cluster nodes are kept under constant monitoring to keep track of their functioning. Whenever a cluster fails to perform, it is either restarted or shifted to another node. 
  • Cluster Shared Volume (CSV): This Fail Over Clustering functionality offers a consistent and distributed namespace that nodes can utilize to work with shared storage. This feature is critical in ensuring minimum disruptions for your server applications.

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Importance of Fail-Over Clustering

The Fail Over Clustering mechanism empowers you to perform patching & maintenance work on the passive nodes without shutting down your database. This way you can prevent downtime issues and can also repair failed servers without causing any delay. Moreover, in cases of a hardware error, this mechanism ensures that the database is stopped to safeguard the active nodes.

You can also experience automated data recovery in case of failure using Fail Over Clustering. This will lessen your dependency on the IT team and will allow your servers to recover in less time. Furthermore, this mechanism provides you with high SQL Cluster availability coupled with minimum downtime. Fail Over Clustering’s automatic failover feature also ensures that your database is always up and working even in face of failure occurring on the hardware level. Using this technique can simplify server management and recovery for your online mechanism.

Types of Fail Over Clusters

In the recent decade, there have been major developments in the field of Fail Over Clustering and many companies provide their own version of clustering solutions. Some of the most popular clustering types are:  

VMWare Fail Over Clusters

The VMWare Fail Over Clustering is a popular mechanism to manage failures of virtual servers. It offers several tools for VM clusters and provides a continuous availability model that accurately replicates a VMware virtual machine. Moreover, VMware’s vSphere HA offers high availability services for your VMs by resting a pool of VMs and their hosts. Since the tool does not depend on any external component, it has a low risk of failure. 

Windows Server Fail Over Cluster (WSFC)

The WFSC mechanism allows you to generate Hyper-V failover servers. This technique gained high popularity among Windows users between 2016 and 2019. WSFC supports cluster monitoring and automatically provides the required failover mechanism. To manage a situation of server failure, WFSC either shifts the clusters to separate node or try restarting them.  Furthermore, its Cluster Shared Volume (CSV) technology provides a distributed namespace to utilize shared memory among multiple nodes.

SQL Server Fail Over Clusters

This Microsoft product, launched in SQL Server 2017, contains powerful HA solutions that leverage WSFC technology. Under this, SQL Server components are considered WSFC cluster resources. They are further integrated with other resources dependent on WSFC. This way, WSFC has the control to identify and communicate the commands to restart an SQL Server instance or to shift such instances to a different node.

Red Hat Linux Fail Over Clusters

The Red Hat Enterprise Linux (RHEL) has designed its technique to manage failovers. Under this Failover Clustering users can easily build HA failover clusters using the Add-Ons and Red Hat Global File System. Moreover, it provides ample support for single clusters that span multiple sites. Such multi-site clusters operate on a Storage Area Network (SAN) based data replication which benefits from Red Hat’s Fail Over Clustering.

Key Processes Involved in Fail Over Clustering

Fail Over Clustering: Before and After
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The Fail Over Clustering consists of the following 2 key processes:

High Availability Fail Over Clusters

A High Availability (HA) Cluster contains a group of independent servers that work by sharing resources & data across the system. This implies every node in the Fail Over mechanism can access the shared storage. Such High Availability Clusters also deploy a monitoring connection that can track the “heartbeat” (health) of the other servers. 

Using the heartbeat mechanism in a simple two-node configuration, the first node can easily recognize the failure of another node. In this scenario, the first node marks itself as active and marks the other node as passive entities. Similarly, for every cluster, the node pairings constantly monitor the health of their pair node and ensure that at least one node is active in every cluster at all times.

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Continuous Availability Fail Over Clusters

In contrast to the High Availability model, the CA (Continuous Availability) mechanism works with clusters that have multiple systems sharing a single copy of the Operating System. This implies commands issued by anyone system are also implemented on the other systems automatically.

The CA Fail Over Clustering requires everyone in the company to use formatted computers. This is necessary to ensure that an updated copy of the OS exists on each computer.

Applications of Failover Clustering

Fail Over Clustering is a robust mechanism which can facilitate the following real-time applications:

  • Ensures Availability of Critical Applications: Online Transaction-based systems require 100 per cent data availability at all times to ensure lossless transactions. Therefore, Fail Over Clustering is highly useful in applications in which online transactions are a key part. For instance, Ticket reservations, stock trading, ATMs, etc., all can benefit from Fail Over Clustering.
  • Disaster Recovery: Disaster Recovery is a key application for Fail Over Clustering. Microsoft also provides storage for saving your replicated data that can provide data recovery in case of a disaster. Furthermore, companies can use the Fail Over mechanism to replicate and store data at various locations so that even if a location is affected by any physical disaster, the remaining replicas are safe.
  • Database Replication: Database providers often provide you with Fail Over Clustering-based database replication features. For instance, MySQL Cluster offers a heartbeat mechanism that can detect failure occurring in other nodes instantly.

Limitations of Fail Over Clustering

Fail Over Clustering comes along with the following limitations;

  • The Fail Over Clustering setup for Windows is complex and requires you to manage multiple networks and network cards simultaneously. Therefore it is not easy for a beginner to deploy this mechanism.
  • There is a need to have a stronger integration between Windows Failover clustering & Hyper-V. Until such integration is developed, you will need to make changes in both of these tools to perform Fail Over Clustering smoothly.
  • This mechanism does not have any web portal that can allow you to modify its cluster settings. You need to manually log into a remote desktop using a VIP address and navigate to the Cluster Manager option.

Conclusion

The article introduced you to Fail Over Clustering and explained its key features. It also explained the importance and sub-processes involved in this mechanism. The article further elaborated on the types, main applications and limitations of using the Fail Over Clustering. 

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