The main requirement for any datacenter, is it’s performance and fault-tolerance, which determines the level of its reliability. That resilience will be fundamental to the flawless operation of the services, provided by the datacenter. The next essential factor is the fast connection speed (bandwidth), and the professional support team. Let us review the levels of reliability:

Tier II class
This kind of datacenters have a standard level of redundancy of resources, used in the engineering equipment. In this case, there may be interruptions in the operation of the equipment. The essential condition for the flawless operation is the back-up resources of power supply and the raised floor, for the efficient cooling system. During repairs or service operations there may be a short interruption of a datacenter operation. This system does not have a full backup of resources, but there are some additional elements installed in the cooling systems and power supply. Regulated downtime for such datacenters is 22 hours per one year of trouble-free operation, reliability rate is 99.741%.

Tier III class
The technical equipment in the datacenter with level of reliability «Tier III» allows to perform repairs or technical service without interrupting of the service. Datacenters of this class have all characteristics of the Tier II class, as well as: 2 or more independent power supplies for uninterruptible operability of the equipment, multiple internet connection links, and reliable cooling system. It is important to take into account the fact that datacenters of this class are equipped with generators for continuous power supply in case of emergency. Regulated downtime for such datacenters is 1.6 hours per one year of trouble-free operation, reliability rate is 99.982%.

Tier IV class
The most reliable and fault-tolerant class of datacenters, is Tier IV class. Datacenters of this class have all characteristics of the Tier II class, as well as: redundant (duplicate) power supply of all components of the air cooling system, including chillers, ventilation systems, and air-conditioning systems. Any service operations, whether it's planned maintenance operations, as well as unplanned emergency repairs are performed without interrupting of the datacenter operations. Failures in the datacenter with a level of reliability Tier IV is possible only in case of activation of the fire-extinguishing system or emergency disconnection of all power supplies. Regulated downtime for such datacenters is 0.4 hours per one year of trouble-free operation, reliability rate is 99,995%.