High Availability vs. Disaster Recovery: What’s the Difference?

As organizations increasingly rely on technology to carry out their operations, it has become essential to ensure that IT systems remain available and functioning. With this heightened reliance and as more organizations modernize their IT infrastructure, global IT spending has grown significantly. And with this bolstered growth, more CIOs are choosing to invest additional budget toward initiatives, like high availability (HA) and disaster recovery (DR) systems, that aim to prevent and resolve potential IT system failures.

Although the two are related concepts that strive to improve resilience, they have clear differences in design, objectives, and goal measurements. Let’s explore high availability vs. disaster recovery and learn about their differences, infrastructure elements, and how they can work together.

What is High Availability and How Does it Work?

In computing, the term “high availability” is used to describe an IT system, service, or application that can be continuously operational, handle different workloads, and deliver quality performance with minimal (if any) downtime or interruption during:

• Scheduled outages
• Unexpected outages

HA serves as a failure response mechanism and uses a combination of industry best practices and techniques to eliminate single points of failure. HA is determined and measured by meeting specific uptime goals – but how are those generated? By calculating the high availability percentage, which is the metric IT teams use to measure the reliability, performance, and uptime of their organization’s systems and services. Often, this number is meant to serve as a baseline to set service level agreements (SLAs) between service providers and their customers, where the provider promises a minimum level of availability for the service.

Calculating a High Availability Percentage

This percentage is calculated by dividing the total time the system was available by the total time it was supposed to be available:

• Availability percentage = (Time supposed to be available – downtime) / time supposed to be available x 100%

For example, if a system was supposed to be available 24×7 (720 hours) in a month but experienced 30 minutes of downtime, then the availability percentage for that system would be calculated as follows:

• Availability percentage = (720 – .5) / 720 x 100% = 99.9%

Based on this calculation, the uptime for the service was 99.9%.

4 High Availability Elements and Techniques

Although there are numerous infrastructure elements and techniques that can be used to achieve high availability, here are some of the most common:

• Redundancy: HA IT infrastructure uses redundant components, like backup servers, power supplies, and network connections, to promote software, hardware, application, and data redundancy. The use of these elements ensures that if one piece fails, another can switch on and take over without affecting service availability.
• Replication and failover: Data replication and failover are critical elements to include when building highly available infrastructure. Replication allows IT leaders to continuously make copies of data from virtual machines (VMs) and keep them on a secondary database. If the primary server fails, failover kicks in which means the secondary server starts up and enables users to continue using the most up-to-date copy of their system.
• Load balancing: Load balancing is used to distribute traffic across multiple servers. The purpose? To prevent any one server from being overloaded, thus ensuring that service remains available if another server goes down.
• Monitoring: Monitoring tools can be used to detect issues before they become critical problems, allowing IT teams to act before service is interrupted.

What is Disaster Recovery and How Does it Work?

Disaster recovery is a detailed process that restores a company’s critical systems, infrastructure, services, and data after a natural disaster or other disruptive event, like a ransomware attack or general human error. Building a DR plan is extensive, and includes many components, such as: identifying all possible risks, preparing responses to potential scenarios, determining whether DR should be in the cloud or on-premises, procedures for protecting and recovering data and systems, among others.

Since each DR plan and its respective checklist, recovery time objectives (RTOs) and recovery point objectives (RPOs) are uniquely designed around the needs and capabilities of the company, the exact way DR works varies. In general, when a DR plan is activated, IT teams work to restore business systems and data to minimize downtime, prevent data loss, and get back to “business as usual” as quickly as possible. 

Disaster Recovery Infrastructure Elements

DR infrastructure elements are designed to ensure that an organization’s critical business systems and data can be safely restored quickly and efficiently in the event of a disaster. Since DR plans are multifaceted, the elements utilized within each plan can vary so it’s hard to pinpoint exact infrastructure components. However, a few common DR infrastructure elements are:

• Backup and recovery solutions
• Continuous data replication
• Redundant hardware, software, and networks
• Offsite data storage, usually in a third-party data center

What Makes High Availability Different from Disaster Recovery?

While HA and DR are related concepts that are often used in conjunction, they have distinctive purposes. HA focuses on minimizing downtime and maintaining the continuous availability of IT systems, services, and data. DR, on the other hand, revolves around utilizing a comprehensive plan to restore systems, services, and data after a disaster. HA is meant to prevent any downtime from happening in the first place while DR focuses on recovering from a disruption or failure that has already occurred.

3 High Availability and Disaster Recovery Differences

• Preventative vs. solution: HA is a preventative system whereas DR is a solution to a disaster.
• System design and organizational policies: HA is all about making sure IT systems are designed in a way that avoids system failure while DR’s purpose is to use tools, policies, and procedures to enable recovery after a disruptive event.
• Objectives and measures: The objective of HA systems is maintaining availability using high availability percentage metrics whereas DR systems depend on setting and meeting RTOs and RPOs.

3 High Availability and Disaster Recovery Similarities

• Ensure business continuity and fault tolerance: Both operate according to a main goal of ensuring business operations continue with minimal disruption if one or more components fail.
• Redundancy: Each system aims to eliminate points of failure to ensure redundancy.
• Risk mitigation: HA and DR involve preparing for and mitigating risks that can impact business services.

How Do High Availability and Disaster Recovery Work Together?

HA and DR are both important strategies that organizations use to ensure their business processes continue to function despite unexpected events. They reinforce each other, and play crucial roles in how IT teams:

• Navigate interruptions
• Maintain uptime
• Recover data

When paired, these two concepts are the key to creating a comprehensive approach to system availability and resilience. How? High availability elements can be used to reduce the need for disaster recovery, and disaster recovery can serve as a backup plan if high availability mechanisms fail.

How to limit the impact of disruptions

Developing a solid plan of how to maintain business continuity in the event of a disaster is a top priority for many CIOs in 2023, however, getting started can be tough. At TierPoint, our team is ready to help you prevent and limit the impact of potential disruptions to your data, applications, and infrastructure. Schedule a consultation with one of our experts to learn how Disaster Recovery as a Service (DRaaS) can minimize data loss, secure your mission-critical systems, and more.

In the meantime, download The Ultimate Guide to Running Your Business Through Uncertainty and Disruption to discover what you can do to overcome challenges around business continuity.