With a standalone server web hosting, all web services run on one single machine which may become too much to handle for a single machine to handle.
One server has to cope with multiple web sites and thus this is a reason you sometimes find a web site inaccessible. Clustered hosting aims to alleviate this problem by sharing the burden of running website programs across several servers. It is a type of web hosting that spreads the load of hosting across multiple physical machines, increasing availability and decreasing the chances of one service affecting another. Since the websites are distributed across various servers, working on one website won't in any way affect another web site. Therefore it sort of protects one web site from the other. Sudden traffic surges will no longer cause your website to run slowly. With clustered hosting you have access to a cluster of web servers which means you also have access to a large variety of resources that could make your web site succeed. You don't even need to upgrade. Any extra power that may be needed will be drawn from a cluster of available services.
With a normal web hosting service, you are usually limited by how much bandwidth, disk space, processing speed, RAM, and other resources that have been allocated to your hosting account and all these hurdles are overcome when you go in for clustered hosting because you now have access to infinite amount of hardware. If you have problems of rebooting and upgrades, then clustered hosting has the ultimate solution. Web sites can be kept running on other servers in the cluster whilst the reboot or software upgrade is rolled out across individual servers by degrees.