What are the specialty for Tier-III and Tier-IV Data center facilities?

Tier3 

1) All Tier1 and2 requirements.

2) Multiple independent distribution paths serving IT equipment. Generally, only one distribution path serves equipment at any given time.

3) All IT equipment is dual-powered and fully compatible within the topology of a site's architecture.

Tier4

1) All Tier1,2 and3 requirements.

2) The facility is fully fault-tolerant, through electrical, storage and distribution networks.

3) All cooling equipment is independently dual-powered, including HVAC systems.

4) There are2 power sources too i.e. power from2 different electrical service provider

TIER-III can work with 1 mda(main distribution area) inside data center and 1 outside but TIER-IV shall required both MDA should be outside of data center.

1.Tier 3 and 4 both will serve all requirements of Tier 1 and 2 requirements.

2.In Tier 3 datacentre, all equipment's should be dual powered, and redundant and should have distributed architecture.

3. Tier 4 datacentre should satisfy all Tier 3 datacentre requirement. In addition to that, it should have dual powered cooling systems like chillers, HVAC . Also site infrastructure should be fault tolerant and should have power storage of generation facility,

The prime difference between TIER III & TIER IV is the Uptime of the Facility by means of increasing the redundancy level of the Distribution (Mechanical & Electrical) & Critical Components (Mechanical & Electrical Equipment). TIER III talks about Concurrently Maintainable Facility & TIER IV talks about Fault Tolerant Facility.  

Tier3 

All Tier1 and2 requirements.Multiple independent distribution paths serving IT equipment. Generally, only one distribution path serves equipment at any given time.

Tier4

All Tier1,2 and3 requirements.The facility is fully fault-tolerant, through electrical, storage and distribution networks.All cooling equipment is independently dual-powered, including HVAC systems.

Tier 3 = Tier 1 + Tier 2 + Dual-powered equipment and multiple up-links.

Tier 4 = Tier 1 + Tier 2 + Tier 3 + all components are fully fault-tolerant including uplinks, storage, chillers, HVAC systems, servers etc. Everything is dual-powered.

Refer to TIA 942 standards for a better understanding on this.

Hi Tarique, 

I wrote a small article about datacenter tiers , hope that will full fill you ask please fine the link for the same "http://www.unixdcbees.com/datacentertiers/" .

Thanks & Regards,

Vijaybabu.A 

Tier III 

Tier III certified data centers are often referred to as three 9s. Most enterprises select Tier III data centers for their uptime and redundancy measures. There is a huge jump in the availability of a Tier III data center opposed to a Tier II data center. A Tier III facility has availability of 99.982% with only 1.6 hours of interruption a year. [2]

A Tier III data center has N+1 Redundancy. N+1 means that the facility has what is required to operate plus a backup. Redundancy can include items like power feeds, diverse network paths, UPS, and diesel generators.

Tier IV 

The Tier IV certification is currently the highest classification among data center facilities. In fact, Tier IV facilities are the equivalent of data centers used by the United States Government. They are highly secure, reliable, and redundant.

Tier IV is sometimes referred to as the four 9s. Tier IV data centers have an availability of 99.995% and 0.8 hours of interruption per year compared to 1.6 hours of interruption with a Tier III facility. That is half of the downtime represented by a Tier III data center.

Tier IV facilities hardly ever experience downtime and when they do it is only for a fraction of a second while failovers switch to alternative systems. There are Tier IV certified data centers that count the days and hours since their last interruption with some spanning years.

As far as redundancy, a Tier IV facility typically features 2N+1 Redundancy. The term 2N+1 means that the facility has two times what is required to operate plus a backup.

The word Tier is changed to Rating in Tia-942. For rating3 / tier3, components & paths have N+1 configuration with one active and one passive. and it is concurrently maintainable and can sustain one planned maintanance. 

However in tier4 / Rating4 both paths / components work in active-active mode and can sustain one fault at a time.