Software High Availability Cluster vs Fault-Tolerant System

Evidian SafeKit

Comparison between a software high availability cluster vs a fault-tolerant system

The deployment of a software high availabiliy cluster as implemented by SafeKit is much more flexible than a fault tolerant system. The following table explains why.

Flexibility of a software high availability cluster vs a fault tolerant system

Software high availability cluster

SafeKit high availability vs fault-tolerance

Fault-tolerant system

Système tolérant aux fautes


SafeKit on Windows and Linux

Fault tolerant products


No dedicated server.

Each server can be the failover server of the other one for multiple applications.

Dedicated hardware.

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


Smooth upgrade/fix of application and OS possible server by server.

N and N+1 versions can coexist.


Same application and OS image on both servers.


The recovery time with SafeKit (RTO) depends on the time to detect and to restart the application (about 1 minute).

The data loss with SafeKit (RPO) 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.


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

Environment where hardware failures is the main concern

Example of a software high availability cluster with Microsoft SQL Server

SafeKit Modules for Plug&Play High Availability Solutions

Demonstrations of SafeKit High Availability Software

SafeKit Webinar

This webinar presents in 10 minutes Evidian SafeKit.

In this webinar, you will understand:

  • mirror and farm clusters
  • cost savings against hardware clustering solutions
  • best use cases
  • the integration process for a new application

Microsoft SQL Server Cluster

This video shows a mirror module configuration with synchronous real-time replication and failover.

The file replication and the failover are configured for Microsoft SQL Server but it works in the same manner for other databases.

Free trial here

Apache Cluster

This video shows a farm module configuration with load balancing and failover.

The load balancing and the failover are configured for Apache but it works in the same manner for other web services.

Free trial here

Hyper-V Cluster

This video shows a Hyper-V cluster with full replications of virtual machines.

Virtual machines can run on both Hyper-V servers and they are restarted in case of failure.

Free trial here