The Quality of Service (QoS) and the Service Level Agreement (SLA) must be outlined with the website or online service’s users. For example, there is no reason to host the service in a high-availability data center (Tier IV) if the users are prepared to accept an availability of equal to or under 99% for a non-critical service. With equal energy efficiency, the more data center hosting the website or online service is available, the larger its overall environmental footprint. This is primarily because everything is mirrored and active, with dual-powered electricity and dual-powered cooling systems, etc.
Despite their hundreds of millions of users, the giants of the internet do not offer Tier IV high availability. Data is mirrored on at least one other server in another data center. If a server goes down, the user is automatically diverted to the backup server. This action takes a few seconds, which is perfectly acceptable and almost unnoticeable for the end user.