A Server Mirroring configuration requires 2 identical dedicated servers, one of which will be classified as the master server and the second will be the slave server. Whilst the master server will be the machine that does the bulk of the work and serves your websites, the slave server will be in constant synchronisation with the master server as to ensure that an identical copy of the contents of the master server is always available on the slave server. The purpose of Server Mirroring is to provide up to 100% guaranteed uptime by providing a failover-proof solution; if the master server ever fails then the tasks performed by the this server will automatically be taken over by the slave server with the transition between the two being seamless. Server Mirroring is a great way to compliment your Disaster Recovery (DR) arrangements or to introduce redundancy into your hosting infrastructure.

Benefits to your organisation of employing the Server Mirroring architecture include:

  • Your data will be constantly backed up onto your slave server, therefore meaning that in the event of the master server suffering downtime, your websites and applications will remain online without any data loss being incurred
  • Webhosting UK's Server Mirroring solution can be used to compliment any Disaster Recovery plan with disk-to-disk synchronisation being used constantly
  • A new level of redundancy can be introduced to your hosting infrastructure with server resources being used efficiently to create a highly reliable configuration.

Replication of Data

Webhosting UK utilises two primary technologies to keep the data between the master and slave servers in constant synchronisation: FAM and rSync. The servers used in the configuration need to be either of a same or similar specification so that there is no noticeable performance difference when the transition between the two takes place. When a file on the master server is updated, it flags itself and FAM is notified about this; rSync is then sent a request by FAM to copy the updated file to the slave server – as this process is completed very quickly, there is no noticeable impact on the availability of system resources.

Server Monitoring

Failover occurs when the slave server has to take over the roles of the responsibilities of the master server because the master server is unavailable; in this situation, all requests that would normally be sent to the master server are instead routed to the slave server. We put in place a monitoring script to ensure that there is no downtime incurred during the failover process. Once the slave server is aware that the master server is unavailable, it will automatically bind the secondary IP address (because this is the shared IP for websites) of the master to itself, along with any other dedicated IP addresses that are being used for individual websites and services. Once this process has completed, websites will then begin to be served from the slave server and because this changeover only takes a couple of seconds, there will be no noticeable downtime.


If any data loss has occurred on the master server then this can be easily restored from the slave server once the master server is back online. Whilst there is no need to investigate individual files because this is done by rSync, you will need to select the restoration target and the set of data that you wish to replicate on the master server. In any case you should aim to perform the replication process if the slave server has ever been put into use because once data has been changed on the slave server, the data on the two machines will fall out of synchronisation; it is important for the data on the two machines to remain consistent in order for Server Mirroring to be effective.

Webhosting UK offers a range of Enterprise-class server solutions to help boost your business's online presence. Whether you require a DR solution to ensure that you suffer neither data loss or downtime or a highly redundant dedicated server cluster for the hosting of popular web applications then our sales team will be able to assist you with finding a solution to your needs.

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