Fault Tolerance vs High Availability – Choose The Right Methodology For Systems & Application Availability

fault tolerance vs high availability

Businesses rely heavily on servers and infrastructure to keep applications connected and running smoothly. Visitors also expect these applications to work anytime and every time they access these apps.

However, unexpected outages and planned maintenance of critical application components and underlying hardware equipment can disrupt users’ access. This downtime decreases the quality of the user experience and results in adverse customer reactions and loss of reputation.

Table Of Content

  1. What is Redundancy?
  2. What is Fault Tolerance?
  3. Advantages of Fault Tolerance
    1. Zero Interruption
    2. No Loss of Data
  4. Disadvantages of Fault Tolerance
    1. Complex System Implementation
    2. Higher Costs
  5. What is High Availability?
  6. Advantages of High Availability
    1. Cost Savings
    2. Easily-Scalable
    3. Simple Load-Balancing Solutions
  7. Disadvantages of High Availability
    1. Service Hiccups
    2. Required Component Duplication
    3. Data Loss (Rare)
  8. Conclusion
  9. FAQs

There are two main ways to ensure critical applications and infrastructure availability to minimize interruptions due to errors, failures, and unexpected errors.

Fault-Tolerance (FT) and High Availability (HA). Utilizing either of these choices will help you minimize (or even eliminate) connectivity issues for the inter-connected system components.

The debate of Fault-Tolerance vs High-Availability has attained more significance these days when SaaS has become the dominant way of delivering software to many customers.

Let’s start with the definition of redundancy and then go into the details of Fault Tolerant and High Availability paradigms.

What is Redundancy?

Redundancy refers to having two (or more) servers with duplicate or mirrored data. Fault tolerance helps ensure that the core business operations stay connected and available online, whereas redundancy concerns the duplication of hardware and software resources. On the other hand, High Availability offers automatic failover in case of a failure, whereas redundancy involves minimizing points of hardware or software failures.

What is Fault Tolerance?

Fault tolerance is a form of redundancy that ensures visitors can access and utilize the system, even when one or more components becomes unavailable for any reason. In the fault tolerance vs high availability debate, fault tolerance allows users to use the application or view the webpages with limited functionality. Unlike high-availability systems, fault-tolerant systems don’t aim to keep all systems up and running with automatic failovers to other working nodes/components of the system.

Fault-tolerant systems are designed to withstand almost any type of failure since there is no crossover event. Instead, several redundant system components store copies of user requests and changes to data. As a result, if one component fails, the others can pick up the slack. This makes fault-tolerant systems the perfect solution for mission-critical applications that cannot allow or afford downtime.

A good example of a fault-tolerant system is a storage area network (SAN). A SAN is a scalable central network storage cluster for critical data that is fault-tolerant, thanks to low latency ethernet connections directly to the servers in the cluster. With a SAN, users can transfer data sequentially or in parallel without affecting the host server’s performance.

Advantages of Fault Tolerance

Now that you know about the idea of fault tolerance, we will look at the benefits of this idea. The list includes:

Zero Interruption

The main distinction between high availability and fault tolerance is that fault tolerance provides zero service interruption to all clients. This means that end-users can rely on the system to be up and running at all times. The provider can deliver services without interruptions, such as:

A fault-tolerant system is designed to continue operating even during a component failure. A backup component automatically takes over if a component fails, so there is no downtime or data loss. This is an important point in the debate of high availability vs fault tolerance because a highly available system is designed to prevent component failures from happening in the first place.

No Loss of Data

Fault-tolerant systems generally have lower data loss incidents because there is no component crossover. As a result, the system continues to accept, process, and write data during an incident.

Disadvantages of Fault Tolerance

The idea of Fault Tolerance systems does have some disadvantages, such as:

Complex System Implementation

By design, fault-tolerant systems have a complex design to manage users’ requests and traffic volume while duplicating information. It takes time and considerable effort to mirror information (and resources) from both hardware and software standpoints. As a result, designers often need to build subsystems to handle data and request mirroring and serving responses to the end-users.

In practical terms, this means parallel processing of user requests within a fault-tolerant system. Unfortunately, this complicated multi-node design has more opportunities for design failures that can eventually bring down the entire system.

This complexity is an important factor in the Fault-Tolerance vs High-Availability decision process.

Higher Costs

When it comes to cost, businesses must weigh the pros and cons of investing in a fault-tolerant system. While such systems have many advantages (such as providing security and connectivity during unexpected issues), they also come with higher setup and maintenance costs. In addition, the requirements for hardware and software components can get expensive, and you need to hire additional team members for system management.

So, when deciding whether to invest in a fault-tolerant system, businesses must decide if the benefits are worth the costs. Alternatively, if a few microseconds of connectivity issues during a crossover in a High Availability system is not a major issue, perhaps the business can do without the higher costs of a fault-tolerant setup.

What is High Availability?

High availability systems are created to have extended uptime by eliminating all possible points of failure that could cause mission-critical applications or websites to go offline during unfortunate events, such as an increase in traffic, malicious attacks, or hardware malfunction.

In simple words, redundancy is crucial in achieving high availability – you need one to have the other. This is achieved by implementing various levels of replication and failover capabilities into an infrastructure so that if one component fails, another one can immediately step in and take its place without any user-facing downtime.

The most interesting aspect of a High availability system is how a backup takes over automatically if a component fails. The process is software-based and uses a monitoring component to identify failures and initiate a transfer of traffic or resources to the backup component or machine. This ensures your services are always available and running smoothly.

Advantages of High Availability

Now that we have learned about High Availability, it’s time to discuss the advantages of the approach and the factors that play an important role in deciding high availability vs fault tolerance.

Cost Savings

The main advantage of high availability systems is that they are easier to design and implement. As a result, they cost less than fault-tolerant designs. High availability systems are simpler, which makes them easier to use and maintain.

Easily Scalable

Highly available solutions are also easily scalable – which is excellent news for infrastructure designers! The simplest way to introduce a highly available system is to use duplicate infrastructure, meaning the system’s capabilities can be increased without much investment in design. This speeds up the scaling of the system without requiring a lot of time and resources.

Simple Load-Balancing Solutions

Highly available systems are a great way to provide load-balancing without adding extra infrastructure. In this setup, traffic is split between multiple environments, which helps distribute the workload and manage traffic and requests in the event of a failure.

For example, half of your website traffic can go to server A while the other half goes to server B. This split reduces the load on each server and results in a smoother user experience.

Now, in case of a failure at either of the servers, the event is detected by the monitoring component, and the traffic and requests coming to the failing server are diverted to alternate resources. End-users often don’t feel any difference at the frontend when this happens.

Disadvantages of High Availability

In the fault tolerance vs high availability debate, you’ll find that the following pointers are quoted as the disadvantages of the HA systems.

Service Hiccups

A crossover event in a high availability system is when traffic is moved or redirected from failing systems to ones still operational. This process involves several factors, such as:

  • The software monitoring component that determines if there is a failure
  • Differentiating between failures and false positives (for example, when there is just heavy traffic or a lost packet)
  • The event that alerts the need to crossover to a healthy system

Even though the process is fast, users may experience a brief outage (no more than a few seconds) while the crossover occurs. However, this outage is much shorter (and less noticeable) than a complete interruption in service that would happen if there was no crossover event.

Required Component Duplication

High-availability systems are generally built by duplicating the components to protect against outages and failures.

Resource duplication has a cost, but it is generally lower than the potential loss in revenue that results from hours-long service outages.

The cost of duplication is like insurance: You regularly pay for the “just in case” event.

Data Loss (Rare)

The most detrimental factor during a service disruption is not the interruption of service but potential data loss. In most cases, the system resends users’ requests to secondary components in the changeover event. However, in systems with a very high data movement rate, there is a chance of loss during the changeover event.


Fault tolerance vs high availability is an ongoing discussion in systems architecture and services delivery. Both approaches are used to build systems that increase the reliability and availability of systems, scripts, and applications.

Fault tolerance focuses on the ability of a system to continue functioning normally in the event of component failure. In contrast, high availability focuses on the ability of a server to remain available and accessible to users with minimal downtime.

At RedSwitches, we consider both as essential aspects of a comprehensive services delivery and data protection strategy. We help our clients build systems that come with regular backups and disaster recovery solutions to protect data and ensure sustained service delivery during a failure.


1. What is Fault Tolerance?

Fault Tolerant computer systems aim to maintain business continuity and high availability. As a result, fault tolerance solutions frequently concentrate on sustained operations of mission-critical systems and applications.

2. How can I add Fault Tolerance to my current operations?

Fault-tolerant servers require low system overhead to ensure high availability and top performance. You can use industry-compliant servers you currently have to run fault-tolerant software.

3. What exactly is a High Available System?

High availability (HA) is the capacity of a cluster to continue executing an application. The application continues to function even when a server system failure would ordinarily render it unavailable.

4. What is the process by which the cluster provides high availability?

The cluster framework offers a highly available environment by implementing a failover process. This process is a sequence of operations that moves data, services, and resources from a failed node or zone to an operational node or area in the cluster.