--- canonical: "https://safekit.eviden.com/products/high-availability-software-for-application-clustering/high-availability-cluster-vs-fault-tolerant-system/" llms_index: "https://safekit.eviden.com/llms.txt" llms_section: "Key Concepts & Educational Content" topics: "HA Cluster vs. Fault Tolerant System: Choosing the Right Redundancy Strategy, SafeKit SANless HA Cluster: A Software Alternative to Fault Tolerant Hardware, What is the difference between high availability and fault tolerance?, Pros and cons of high availability and fault tolerance, 🔍 SafeKit High Availability Navigation Hub" --- # HA Cluster vs. Fault Tolerant System: Choosing the Right Redundancy Strategy ## SafeKit SANless HA Cluster: A Software Alternative to Fault Tolerant Hardware [🧑 Contact us](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/contact-us-for-safekit/) [🎁 SafeKit free trial](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/safekit-free-trial/) [🏅 Free certification](https://training.my.evidian.com/mod/page/view.php?id=712) [💰 Perpetual license cost](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/get-a-quote-safekit-en/) ## What is the difference between high availability and fault tolerance? ### Overview 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... The following comparative tables explain in detail the difference between a fault tolerant system and SafeKit, a software high availability cluster. ### What is high availability? 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. Hardware clusters are based on shared disks resulting in dependencies between servers and their connections to shared disk arrays. 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. ### What is fault tolerance? 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. Fault-tolerant systems only deal with hardware failures and not software failures, by far the most common reason for system downtime. ## Pros and cons of high availability and fault tolerance | | | | --- | --- | | **Software high availability cluster** Active active high availabilityActive active high availability | **Fault-tolerant system** Fault tolerance with lockstep CPUFault tolerance with lockstep CPU | | **Product** | | | [SafeKit on Windows and Linux](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/) | Fault tolerant products | | **Hardware / hypervisor** | | | 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 [server can be the failover server of the other one for multiple applications](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/active-active-cluster-real-time-replication/). | Dedicated hardware or dedicated hypervisor. The secondary server is dedicated to the execution of the same application synchronized at the instruction level. | | **Software failure** | | | Software failure supported with restart in another OS environment. | Software exception on both servers at the same time on the same OS. | | **Smooth upgrage/fix of application and OS** | | | Yes Smooth upgrade/fix of application and OS possible server by server. N and N+1 versions can coexist. | No Same application and OS image on both servers. | | **RTO/RPO** | | | The recovery time with SafeKit ([RTO](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/what-is-rpo-and-rto-with-examples/)) depends on the time to detect and to restart the application (about 1 minute). The data loss with SafeKit ([RPO](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/what-is-rpo-and-rto-with-examples/)) is zero as the replication is synchronous. | The recovery time (RTO) of a fault tolerant system is zero. The application is not restarted in case of failure and continue its execution on the secondary server. The data loss (RPO) is also zero. | | **Flexibility** | | | Can run on any type of server with standard Windows and Linux OS | Depends on specific hardware or on specific hypervisors | | **Suited for** | | | [Software editors which want to add a simple high availability option to their application](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/application-clustering-software/) | Environment where hardware failures is the main concern | ## 🔍 SafeKit High Availability Navigation Hub Explore SafeKit: Features, technical videos, documentation, and free trial | Resource Type | Description | Direct Link | | --- | --- | --- | | **Key Features** | Why Choose SafeKit for Simple and Cost-Effective High Availability? | [See Why Choose SafeKit for High Availability](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#why-choose-safekit-for-ha "Discover SafeKit features for simple and cost-effective high availability") | | **Use Cases** | Explore How SafeKit Ensures the High Availability of Critical Infrastructure | [See All Use Cases (OEM Software, Edge Servers, SCADA, and more)](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-use-cases "Explore SafeKit high availability use cases") | | **Deployment Model** | All-in-One SANless HA: Shared-Nothing Software Clustering | [See SafeKit All-in-One SANless HA](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#all-in-one-sanless-ha "Learn about all-in-one SANless high availability with shared-nothing software clustering") | | **HA Strategies** | SafeKit: Infrastructure (VM) vs. Application-Level High Availability | [See SafeKit HA & Redundancy: VM vs. Application Level](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-redundancy-choices "Compare VM-level redundancy with SafeKit application-level high availability strategies") | | **Technical Specifications** | Technical Limitations for SafeKit Clustering | [See SafeKit High Availability Limitations](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-limitations "Technical requirements and limitations for SafeKit application clustering") | | **Proof of Concept** | SafeKit: High Availability Configuration & Failover Demos | [See SafeKit Failover Tutorials](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-failover-tutorials "Step-by-step videos on SafeKit high availability, from installation to automated failover") | | **Architecture** | How the SafeKit Mirror Cluster works (Real-Time Replication & Failover) | [See SafeKit Mirror Cluster: Real-Time Replication & Failover](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-mirror-cluster "See technical architecture and failover mechanism of SafeKit Mirror Cluster") | | **Architecture** | How the SafeKit Farm Cluster works (Network Load Balancing & Failover) | [See SafeKit Farm Cluster: Network Load Balancing & Failover](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-farm-cluster "Technical overview of SafeKit Farm Cluster architecture with network load balancing") | | **Competitive Advantages** | Comparison: SafeKit vs. Traditional High Availability (HA) Clusters | [See SafeKit vs. Traditional HA Cluster Comparison](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-comparison "Detailed comparison of SafeKit software vs traditional hardware-based HA clusters") | | **Technical Resources** | SafeKit High Availability: Documentation, Downloads & Trial | [See SafeKit HA Free Trial & Technical Documentation](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-technical-resources "Access SafeKit free trial, technical documentation, and high availability white papers") | | **Pre-configured Solutions** | SafeKit Application Module Library: Ready-to-Use HA Solutions | [See SafeKit High Availability Application Modules](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-application-modules "Browse the library of pre-configured SafeKit modules for automated application failover") | [🧑 Contact us](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/contact-us-for-safekit/) [🎁 SafeKit free trial](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/safekit-free-trial/) [🏅 Free certification](https://training.my.evidian.com/mod/page/view.php?id=712) [💰 Perpetual license cost](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/get-a-quote-safekit-en/)