---
title: "HA Cluster vs. Fault Tolerant System: Choosing the Right Redundancy Strategy"
description: "HA Cluster vs. Fault Tolerant System: Choosing the Right Redundancy Strategy What is the difference between high availability and fault tolerance?"
canonical: "https://safekit.eviden.com/best-practises/high-availability-cluster-vs-fault-tolerant-system/"
topics: "What is the difference between high availability and fault tolerance?, Pros and cons of high availability and fault tolerance, 🔍 SafeKit High Availability Navigation Hub"
category: "best-practises"
lang: "en"
---

<h1 id="ha-cluster-vs-fault-tolerant-system-choosing-the-right-redundancy-strategy">HA Cluster vs. Fault Tolerant System: Choosing the Right Redundancy Strategy</h1>
<h2 id="what-is-the-difference-between-high-availability-and-fault-tolerance">What is the difference between high availability and fault tolerance?</h2>
<h3 id="overview">Overview</h3>
<p>This article explores the pros and cons of a high availability cluster versus a fault tolerant system by looking at hardware constraints, software failures, RTO, RPO&hellip;</p>
<p>The following comparative tables explain in detail the difference between a fault tolerant system and SafeKit, a software high availability cluster.</p>
<h3 id="what-is-high-availability">What is high availability?</h3>
<p>A high availability cluster is based on two servers with restart of the critical application in the event of hardware or software failures. There are 2 types of clusters: hardware clusters and software clusters.</p>
<p>Hardware clusters are based on shared disks resulting in dependencies between servers and their connections to shared disk arrays.</p>
<p>Software clusters like SafeKit are based on real-time data replication and are hardware-agnostic: they can be deployed on physical or virtual servers or in the cloud.</p>
<h3 id="what-is-fault-tolerance">What is fault tolerance?</h3>
<p>A fault tolerant system relies on either specialized hardware or specialized hypervisor to detect a hardware failure and instantly switch to a redundant hardware component without application restart.</p>
<p>Fault-tolerant systems only deal with hardware failures and not software failures, by far the most common reason for system downtime.</p>
<h2 id="pros-and-cons-of-high-availability-and-fault-tolerance">Pros and cons of high availability and fault tolerance</h2>
<p>When protecting critical applications against failures, two main approaches exist: <strong>software high availability clustering</strong> and <strong>fault-tolerant systems</strong>. Each approach offers different trade-offs in terms of cost, flexibility, recovery time, and hardware requirements. Understanding these differences helps choose the right solution for your specific needs.</p>
<p><strong>Comparison of software high availability clustering vs fault-tolerant systems</strong></p>
<table>
<thead>
<tr>
<th>Criteria</th>
<th>Software high availability cluster</th>
<th>Fault-tolerant system</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>Product</strong></td>
<td><a href="/">SafeKit on Windows and Linux</a></td>
<td>Fault tolerant products</td>
</tr>
<tr>
<td><strong>Hardware / hypervisor</strong></td>
<td>No dedicated server, no dedicated hypervisor. Works with the standard and free hypervisor of Windows, Hyper-V, included in Windows kernel for servers and PCs. Works with the standard and free hypervisor KVM (Kernel-based Virtual Machine) integrated in mainline Linux kernel. Each <a href="/architectures/active-active-cluster-real-time-replication/">server can be the failover server of the other one for multiple applications</a>.</td>
<td>Dedicated hardware or dedicated hypervisor. The secondary server is dedicated to the execution of the same application synchronized at the instruction level.</td>
</tr>
<tr>
<td><strong>Software failure</strong></td>
<td>Software failure supported with restart in another OS environment.</td>
<td>Software exception on both servers at the same time on the same OS.</td>
</tr>
<tr>
<td><strong>Smooth upgrade/fix of application and OS</strong></td>
<td>Yes — Smooth upgrade/fix of application and OS possible server by server. N and N+1 versions can coexist.</td>
<td>No — Same application and OS image on both servers.</td>
</tr>
<tr>
<td><strong>RTO/RPO</strong></td>
<td>The recovery time with SafeKit (<a href="/best-practises/what-is-rpo-and-rto-with-examples/">RTO</a>) depends on the time to detect and to restart the application (about 1 minute). The data loss with SafeKit (<a href="/best-practises/what-is-rpo-and-rto-with-examples/">RPO</a>) is zero as the replication is synchronous.</td>
<td>The recovery time (RTO) of a fault tolerant system is zero. The application is not restarted in case of failure and continues its execution on the secondary server. The data loss (RPO) is also zero.</td>
</tr>
<tr>
<td><strong>Flexibility</strong></td>
<td>Can run on any type of server with standard Windows and Linux OS</td>
<td>Depends on specific hardware or on specific hypervisors</td>
</tr>
<tr>
<td><strong>Suited for</strong></td>
<td><a href="/use-cases/application-clustering-software/">Software editors which want to add a simple high availability option to their application</a></td>
<td>Environment where hardware failure is the main concern</td>
</tr>
</tbody>
</table>
<p><strong>In summary</strong> , software high availability with SafeKit provides a cost-effective, flexible solution that runs on standard hardware and supports rolling upgrades, with near-zero downtime (RTO ~1 minute) and zero data loss. Fault-tolerant systems offer instant failover (RTO = 0) but require dedicated hardware and lack flexibility for independent software updates.</p>
<h2 id="hub">🔍 SafeKit High Availability Navigation Hub</h2>
<p><strong>Explore SafeKit: Features, technical videos, documentation, and free trial</strong></p>
<table>
<thead>
<tr>
<th>Resource Type</th>
<th>Description</th>
<th>Direct Link</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>Key Features</strong></td>
<td>Why Choose SafeKit for Simple and Cost-Effective High Availability?</td>
<td><a href="/#why-choose-safekit-for-ha" title="Discover SafeKit features for simple and cost-effective high availability">See Why Choose SafeKit for High Availability</a></td>
</tr>
<tr>
<td><strong>Use Cases</strong></td>
<td>Explore How SafeKit Ensures the High Availability of Critical Infrastructure</td>
<td><a href="/#safekit-use-cases" title="Explore SafeKit high availability use cases">See All Use Cases (OEM Software, Edge Servers, SCADA, and more)</a></td>
</tr>
<tr>
<td><strong>Deployment Model</strong></td>
<td>All-in-One SANless HA: Shared-Nothing Software Clustering</td>
<td><a href="/#all-in-one-sanless-ha" title="Learn about all-in-one SANless high availability with shared-nothing software clustering">See SafeKit All-in-One SANless HA</a></td>
</tr>
<tr>
<td><strong>HA Strategies</strong></td>
<td>SafeKit: Infrastructure (VM) vs. Application-Level High Availability</td>
<td><a href="/#safekit-ha-redundancy-choices" title="Compare VM-level redundancy with SafeKit application-level high availability strategies">See SafeKit HA &amp; Redundancy: VM vs. Application Level</a></td>
</tr>
<tr>
<td><strong>Technical Specifications</strong></td>
<td>Technical Limitations for SafeKit Clustering</td>
<td><a href="/#safekit-ha-limitations" title="Technical requirements and limitations for SafeKit application clustering">See SafeKit High Availability Limitations</a></td>
</tr>
<tr>
<td><strong>Proof of Concept</strong></td>
<td>SafeKit: High Availability Configuration &amp; Failover Demos</td>
<td><a href="/#safekit-failover-tutorials" title="Step-by-step videos on SafeKit high availability, from installation to automated failover">See SafeKit Failover Tutorials</a></td>
</tr>
<tr>
<td><strong>Architecture</strong></td>
<td>How the SafeKit Mirror Cluster works (Real-Time Replication &amp; Failover)</td>
<td><a href="/#safekit-mirror-cluster" title="See technical architecture and failover mechanism of SafeKit Mirror Cluster">See SafeKit Mirror Cluster: Real-Time Replication &amp; Failover</a></td>
</tr>
<tr>
<td><strong>Architecture</strong></td>
<td>How the SafeKit Farm Cluster works (Network Load Balancing &amp; Failover)</td>
<td><a href="/#safekit-farm-cluster" title="Technical overview of SafeKit Farm Cluster architecture with network load balancing">See SafeKit Farm Cluster: Network Load Balancing &amp; Failover</a></td>
</tr>
<tr>
<td><strong>Competitive Advantages</strong></td>
<td>Comparison: SafeKit vs. Traditional High Availability (HA) Clusters</td>
<td><a href="/#safekit-ha-comparison" title="Detailed comparison of SafeKit software vs traditional hardware-based HA clusters">See SafeKit vs. Traditional HA Cluster Comparison</a></td>
</tr>
<tr>
<td><strong>Technical Resources</strong></td>
<td>SafeKit High Availability: Documentation, Downloads &amp; Trial</td>
<td><a href="/#safekit-ha-technical-resources" title="Access SafeKit free trial, technical documentation, and high availability white papers">See SafeKit HA Free Trial &amp; Technical Documentation</a></td>
</tr>
<tr>
<td><strong>Pre-configured Solutions</strong></td>
<td>SafeKit Application Module Library: Ready-to-Use HA Solutions</td>
<td><a href="/#safekit-ha-application-modules" title="Browse the library of pre-configured SafeKit modules for automated application failover">See SafeKit High Availability Application Modules</a></td>
</tr>
</tbody>
</table>
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