High Availability: How It Works and Why It’s Important

In today’s digital economy, where organizations increasingly rely on their IT infrastructure to deliver services 24/7/365, downtime is a nightmare. Recently, one of the Big Tech companies lost $100 million in revenue and drove millions of its users to its competitor due to a few hours of outage. For small and midsize businesses (SMBs) with limited budgets and resources, it gets worse. Prolonged downtime can be a death knell for SMBs, forcing them out of business.

One of the most efficient ways to mitigate the risk of downtime is by ensuring the high availability of your IT infrastructure and systems. While it is nearly impossible to do away with downtime completely, implementing the tenets of high availability will ensure that your network remains functional in the event of an outage or IT disruption.

What is high availability?

High availability (HA) is a process that eliminates the single points of failure to ensure that an IT application or system can operate at a high level, continuously, even if one of the IT components it depends on, such as a server, fails. TechTarget defines high availability as “the ability of a system to operate continuously without failing for a designated period of time. HA works to ensure a system meets an agreed-upon operational performance level.”

High availability is significant in many sectors where a service disruption of even a few minutes could drastically impact business outcomes, resulting in substantial financial and reputational consequences. On that front, high availability ensures that systems and applications function correctly for a continuous period when there’s an occasional failure like a server failure or a power outage.

What is an example of high availability?

High availability systems are leveraged in many industries where the processes must remain functional continuously. In the finance and banking sector, for instance, many benefits of high availability come into play, making 24/7/365 availability an absolute necessity for businesses in the domain. Any downtime in their services can have serious implications on their reputation and business. If a financial institution’s online banking system or point-of-sale (POS) system goes down during a high-volume period for example, it would be all over the news by the end of the day, tarnishing the institution’s reputation. Meanwhile, the failure to provide the service leads to unsatisfied customers and, in turn, customer churn.

Another similar use case can be found in the healthcare industry, where the continuous availability of electronic health records (EHR) is crucial in making the right treatment decisions in an operating room (OR). High availability is also critical for systems that provide life support or the distribution of medications since it ensures that patients receive the care they need.

High availability, represented as 99.999% uptime.

How do you measure high availability?

High availability is generally measured in a percentage system where a 100% system denotes a never-failing service that experiences no outage or zero downtime. However, since achieving 100% high availability with complex systems is rare, service availability typically falls between 99% and 100% uptime and is measured in 9s (three 9s:99.9%, four 9s:99.99%, etc.). For example, cloud computing leaders like Amazon, Google and Microsoft have set their cloud service level agreements (SLAs) at three nines, which is 99.9%.

There are several metrics involved in calculating this uptime availability, such as:

  • Mean time between failures (MTBF): The mean time between failures is the average time a system or application remains operational between two failures, which is typically measured in hours. TechTarget defines MTBF as “a measure of how reliable a hardware product or component is.” MTBF is a critical component in understanding the availability and reliability of a system. By estimating it, organizations can plan for contingencies that may occur.
  • Mean downtime (MDT): Mean downtime is the average time for which a system remains non-operational.
  • Recovery time objective (RTO): The recovery time objective is the amount of time that an organization can tolerate before which business systems and processes must be restored, in the event of a disaster or failure. In other words, RTO is the time an organization takes to recover after notification of a business disruption.
  • Recovery point objective (RPO): The recovery point objective defines the maximum amount of data that an organization can afford to lose without sustaining significant loss in the event of an outage.

How many nines is high availability?

Since it is nearly impossible to achieve 100% availability, a widely regarded yet difficult-to-achieve standard of availability for emergency response systems is five nines, which means 99.999% availability, translating into 5 minutes and 16 seconds of yearly downtime. Another generally agreed upon industry standard for high availability critical applications like ecommerce is four nines, which means 99.99% availability and translates to 52.60 minutes of downtime annually.

The following chart shows the impact various availability levels (or benchmarks) have on system downtime:

Availability Level Average Yearly Downtime Example
99% 87 hours, 40 minutes Conventional, on-prem server
99.5% 43 hours, 50 minutes Public cloud service
99.9% 8 hours, 46 minutes Public cloud service/ SaaS (Microsoft 365)
99.95% 4 hours, 23 minutes High availability cluster
99.99% 52 minutes, 36 seconds High-end business systems, data centers
99.995% 26 minutes, 18 seconds Virtual fault tolerance
99.999% 5 minutes, 16 seconds Continuous availability


What is the importance of high availability?

High availability is vital for organizations to ensure that their critical systems continue to function properly, even during an outage or disaster. Unplanned downtime will manifest in multiple ways, including lost productivity, data loss, tarnished brand image and customer churn, drastically impacting a business’s future. For organizations, particularly SMBs, that rely on their IT infrastructure, downtime often equates to a death knell.

What are the benefits of high availability?

However, the high availability of applications and systems brings a lot of advantages for businesses, such as:

Maximum flexibility

In today’s digital economy that necessitates 24/7/365 service delivery, high availability applications and systems are necessary. They ensure that your production site remains available and secure all the time.

Streamlined maintenance

Unplanned downtime from an outage or disaster is not the only type of downtime organizations could face. Hardware and software updates and upgrades can also lead to downtime, which the high availability approach can streamline and minimize. While their in-house systems are being modified, organizations can plan to restore their production server in the redundant site and run it there.

100% SLA

For Managed Service Providers (MSPs) that want to deliver high-quality service to their clients, high availability systems are a primary requisite. They help MSPs ensure that their clients’ networks never go down.

Data security

By constantly keeping your applications and systems up and running, you can also ensure that business-critical data is not unauthorizedly accessed or stolen.

Enhanced brand reputation and customer relationships

Frequent — or even rare — service unavailability can lead to unsatisfied customers and customer churn. By ensuring the all-time availability of your systems, you can improve your brand reputation and increase customer retention.

How does high availability work?

To implement a high-availability infrastructure, we must first identify and eliminate the single points of failure. While there’s always a risk of an unforeseen event that could cause a network to fail, the aim is to mitigate it as much as possible and design a high-availability infrastructure.

What are some components of high availability?

Several components support a high-availability IT architecture, including:


Hardware, software, applications and data are all made redundant in a high-availability cluster so that when an IT component — such as a server or database — fails, another component can jump in and perform the task.


Similar to redundancy, replication is also critical to achieving high availability. The nodes within a high-availability cluster must communicate and share information with each other so that any node can step in when the server or network device it supports fails.


Another critical component of a high-availability infrastructure is a failover site that is located off-premises. It enables switching network traffic to the failover system when the primary system fails.

Load balancing

Load balancing is also important in high-availability clusters to ensure that no one server gets overloaded with requests at any time. Load balancers route the traffic and monitor the health of servers, ensuring that your system remains available no matter how many server requests you receive.

What are the major principles to ensure high availability?

Let’s now look at five major principles to follow while designing high-availability systems:

Eliminate single points of failure

Single points of failure are IT components that would make the whole system cease to function when they fail. Imagine if a business only has a single server or a single database to support an application. The server or database failure would consequently cause the application to go down. That’s why doing away with single points of failure is essential.

Reliable crossover or failover

Redundancy and replication should also be carried out in high-availability infrastructure to ensure that a backup component is always there to take over a failed one. This enables the network to switch from one component or node to another with zero downtime and data loss.

Failure detection capability (self-healing) and resilience

The system should have in-built automation to ensure that it can handle failures on its own. It should automatically detect application-level failures as and when they happen, regardless of the causes.

Ensuring no data loss

In the event of an outage, the system must ensure that no data is lost.

Provide both manual and automated failover

During planned maintenance, the system should be able to manually failover and failback to minimize downtime. When failures are detected, it should be able to automatically failover to the host site.

How is high availability different from similar concepts?

High availability is often confused with other data/system availability concepts and terms.  It’s important to understand the differences between them and, in some cases, how they complement each other.

High availability vs. fault tolerance

While high availability and fault tolerance are both approaches aimed at delivering high levels of uptime and ensuring the continuity of the service, they achieve that goal differently. While the high-availability technique adopts a software-based approach to attain total redundancy (a high-availability cluster that locates a set of clusters together), fault tolerance instead has a hardware-based approach.

The fault-tolerant model employs multiple systems that operate in tandem to attain complete redundancy in hardware. The applications are mirrored identically and instructions are executed together so that in the event of a system failure, another system takes over with no loss in uptime. While a fault-tolerant approach protects your business from failing equipment, it may take longer to adapt to complex networks and systems. The method is also expensive and is not effective in the case of software failures.

High availability vs. disaster recovery

Although high availability and disaster recovery are related, their goals are different. High availability is a strategic approach to manage critical but more typical failures in the IT components of an infrastructure, which are relatively easy to restore. However, IT disaster recovery is a comprehensive process for overcoming major IT disasters that can sideline the entire IT infrastructure.

High availability vs. redundancy

While the core focus of the high-availability approach is to implement a failover architecture to failover in the case of a failure, redundancy aims to get rid of the points of software and hardware failure. Redundancy is, in fact, a key component of high-availability architecture.

High availability vs. backup

High availability and backup are two critical aspects that play a complementary role in bolstering an organization’s data protection strategy. To minimize downtime and maximize data availability during a crisis, you need to have the ability to restore data quickly from backup to your production systems. An automated backup solution that can quickly restore your business-critical data is thus essential to ensure the high availability of your systems.

Supplement high availability with backup and recovery

Today, SaaS applications have become a goldmine for most SMBs. The vast majority of their business-critical data goes into the SaaS applications like Microsoft 365, Google Workspace and Salesforce as individual emails, messages, shared files, calendars and so on. SaaS vendors like Microsoft, Google and Salesforce have data centers with state-of-the-art capabilities to ensure the security and integrity of their SaaS applications. However, they do not offer native SaaS backups, which puts the onus of protecting your SaaS data in your hands. You could thus experience significant data loss and downtime in the event of an outage or cyberattack.

We understand how important your SaaS data is for your business. That’s why Spanning presents a remarkably fast backup solution that is secure, affordable and easy to use. Spanning Backup for Microsoft 365, Google Workspace and Salesforce are purpose-built automated SaaS backup solutions that simplify your backup and recovery and give you 100% confidence in the swift recovery of your data. With cutting-edge features like automated daily backups and end-user self-service, you can save significant time, resources and money.

You are just one click away from enterprise-class SaaS data protection. Get a demo now to see for yourself the powerful capabilities of Spanning.

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