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Key Differences Between Fault Tolerance And High Availability

Dec 28, 2022 | Cybersecurity

Businesses rely heavily on their IT infrastructure to conduct day-to-day operations. Even a brief outage event of less than a minute can have devastating consequences, including service interruption and data loss, making it essential to minimize downtime whenever possible.

In the IT industry, it’s vital to consider strategies from both a hardware and software perspective. The two most common strategies for consistent uptime are fault tolerance and high availability, both of which rely on redundancy to protect against software or hardware issues to varying degrees.

Fault Tolerance And High Availability: What Are The Differences?

While both options serve the same purpose — to ensure minimal disruption to normal operations during outages — the best method will depend largely on your business situation. Some organizations require zero downtime, while others can get away with having some business functions operate less optimally during short outages.

What is high availability?

High availability is a strategy that maintains approximately 99.999% uptime for mission-critical applications as possible. It does this by having a secondary system that takes over when a single point in the primary system fails.

The key to any high availability system is load balancing, which ensures that the system can detect failures and divert traffic to one or more components when necessary. In normal operation, a load-balanced system will share traffic across multiple regions. However, the balancer can detect failing systems, such as hardware failures, and divert the workload to a healthy system as soon as failure occurs.

High availability combines software and hardware to create a seamless transition between multiple environments, resulting in close to 100% uptime for critical systems.

High availability systems address software failures by creating a pool of virtual machines and resources within a cluster. These multiple availability zones mean that if the load balancer detects a failure through software monitoring in one availability zone, it can immediately switch to a working availability zone, resulting in no perceptible loss of function.

The same principle applies to hardware — all systems have redundant components for power, cooling, computing, storage, and specialized hardware. These replicated physical components ensure that in the event of a hardware failure, the system is ready with backup servers to ensure close to zero interruption.

The benefits of high availability

High availability strategies offer several advantages that make them worth the investment. These include:

  • Cost savings: While any system that requires duplicated industry-standard hardware and software is expensive, high availability is more affordable than a fault-tolerant system. The lower complexity of HA simplifies maintenance and reduces initial and operating costs.
  • Scalability: HA systems scale well with existing infrastructure, as there is no need for additional design or development — all you need to do is duplicate your current system.

The drawbacks of high availability

No system is perfect, and the same is true for HA. Here are some potential downsides to consider when choosing this redundancy strategy:

  • Service disruption: HA systems undergo a crossover event during a failure. This crossover can take some time, resulting in a short outage that may impact user experience and business operations. However, load balancers and modern sensors reduce this crossover to almost undetectable timeframes.
  • Loss of data integrity: A potentially more detrimental factor for HA systems is the chance for data deletion. The potential for data loss occurs during the crossover event when the primary system goes down before the secondary system kicks in. In most cases, HA systems have safeguards in place, but these are not 100% guaranteed to work during all failure events.

What is fault tolerance?

Fault tolerant systems work similarly to high-availability options but promise almost no downtime for all system users. Fault tolerance depends on having multiple redundant systems that process mirrored data simultaneously. Since all processes occur on all systems, the failure of one system doesn’t produce the minimal downtime that occurs in a high-availability environment. Instead, a fault-tolerant environment delivers a seamless experience even if a whole system cluster fails.

While fault tolerance may be overkill for a simple disaster recovery strategy, it’s essential for some companies, including those that offer cybersecurity services in the Bay Area, that depend on constant uptime.

The benefits of a fault tolerant system

While it’s difficult to achieve fault tolerance, the benefits are essential for companies such as cloud services that lose reputation, money, and customers during service disruption. Benefits of fault tolerance include:

  • No data loss: HA crossovers introduce the potential for data corruption or loss. Since fault tolerance relies on multiple redundant systems operating simultaneously, they do not experience the crossover between a primary and secondary system.
  • No interruptions: Fault tolerance delivers a seamless user experience regardless of system downtime. IT departments can implement potentially disruptive activities — data migrations, software patches, hardware replacements — without interrupting vital business operations.

The drawbacks of a fault tolerant system

While fault tolerance is the ideal tool for maintaining 100% uptime for users, it does have several drawbacks that may make it unsuitable for certain business applications. These drawbacks include the following:

  • Complexity: Fault tolerance relies on multiple systems handling the same information simultaneously. Some applications cannot handle mirrored duplicate data or process simultaneous read/write requests on multiple platforms, resulting in many points of potential concern. Designing and implementing a fault-tolerance system requires extensive planning, development, and constant monitoring and evaluation.
  • Infrastructure costs: Unless you’re a data center that already has multiple systems in place, the cost of running a fault-tolerant system can outweigh the benefits it offers.

Which Is Better For You?

Fault tolerance and high availability systems are ideal for disaster recovery and ensuring business operations remain stable during planned and unexpected outages.

When choosing between one of the two systems, you must consider your needs and resources. High availability may have crossover downtime, but it is significantly more affordable and easier to implement than fault tolerance. However, fault tolerance may be essential and worth the added expense if your business has to guarantee essential services.

Whether you want to know the benefits of managed IT services or need more advice on disaster recovery, we at Renascence Consulting are ready to help. Call us at (510) 552-6896 to schedule a consultation today.

Our History


With over 20 years of industry experience under his belt, the company's CEO possesses a degree in Computer Science and a number of certifications, including MCSE, MCSA, A+ and Network+. From an early age, computers were always a part of his life; dating back to the days of the Apple II. Since that time, he served as everything from system administrator to IT business director within well-established companies, before deciding that consulting was his passion. Leveraging years of technical recruiting, he personally handpicked a select group of specialists proficient in Linux, customized web applications and databases, telephony and cross-platform devices, to ultimately bring your organization to the next level.