Explain: Tier 1 / Tier 2 / Tier 3 / Tier 4 Data Center

Q. What is data center tiers? What is tier 1 data center? Which tier / level is the best for maximum uptime?

A. Tier 1 to 4 data center is nothing but a standardized methodology used to define uptime of data center. This is useful for measuring:

a) Data center performance
b) Investment
c) ROI (return on investment)

Tier 4 data center considered as most robust and less prone to failures. Tier 4 is designed to host mission critical servers and computer systems, with fully redundant subsystems (cooling, power, network links, storage etc) and compartmentalized security zones controlled by biometric access controls methods. Naturally, the simplest is a Tier 1 data center used by small business or shops.

  • Tier 1 = Non-redundant capacity components (single uplink and servers).
  • Tier 2 = Tier 1 + Redundant capacity components.
  • Tier 3 = Tier 1 + Tier 2 + Dual-powered equipments and multiple uplinks.
  • 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.

Data Center Availability According To Tiers

The levels also describes the availability of data from the hardware at a location as follows:

  • Tier 1: Guaranteeing 99.671% availability.
  • Tier 2: Guaranteeing 99.741% availability.
  • Tier 3: Guaranteeing 99.982% availability.
  • Tier 4: Guaranteeing 99.995% availability.

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98 comments… add one
  • Scott Payton Sep 5, 2011 @ 16:58

    There are a few parts to this.
    First, let’s identify the standard. You mention both Tier III and Tier 3. First is designation for Tier under Uptime Institute. The second one (with Arabic number) is TIA-942 designation.
    I’m going to assume in this case, we are talking about Uptime Institute. Under Uptime Institute, you are asking “Dual Power Supply” inside or outside. The answer here, is both from a certain point, and probably more than just what your question is asking.
    Let me try to clarify.
    Tier III (or 3) in both cases is defined as “Concurrently Maintainable”. What that means in this case is, for your power system you must have the ability to remain under critical load (N) while performing maintenance (on your power or cooling systems). For power, that will mean you will likely have A and B power feed, which may or may not both be active at the same time. This will mean you will have at least N+1 UPS (usually on each feed, but there are other options, I’m just using this as an example) which would give your UPS (2)N+1 meaning you have N+1 on A and N+1 on B power feeds. Going back to the source however, this can be a little un-obvious. The reason being is for Tier III and IV sites, the generator set is considered the primary power plant. It is not necessary to have 2 (or even 1) utility power feed to meet the Tier objective, so long as the generator plant is properly setup and configured. I’ll skip that detail for now, as it’s going in the different direction to your question.
    So, from power source (Gen or Utility) you need redundant components (Switches, UPS, Batteries) and redundant pathways for power (At least one active, the other passive, though both active is also allowed), leading to your critical IT load, as well as to your Mechanical Load (though Mechanical Load does not have to be on the UPS for Tier III). The last “gotcha” in the Tier III power issue is dual corded IT equipment. The IT gear itself (Server, Switch, SAN, data circuit) must be dual corded, with one plugged to A feed and one to B feed. If only single cord (as some data circuit gear), then it has to be plugged to an ATS or STS in-rack that then has dual feed cord connection to A and B power feeds.
    TIA is not terribly different, as for the largest part they have borrowed an older Uptime Standard for Tier system which follows about 90% of the Uptime standard. Dual corded in TIA is also required. However, under the new TIA-942-2 standard, Utility Power Feeds for Tier III are designated as N+1 (Which would mean, you would need at least 2 in most cases, or more if any 1 utility feed was not enough power to carry the DC load). The rest of the power issues going forward from that point are the same as Uptime Institute.

    If you need more clarity around the engine generator plant let me know but that didn’t seem to be your question, and there are significant gaps in this space between the two standards.

    I know it’s a little convoluted, and I hope this helps.
    Best regards,
    Scott Payton ATS, CDCS

    • Ksomer Mar 5, 2012 @ 17:22

      Dear Scott ,
      would you please provide more clarity around the engine generator plant and whether to use single ATS for the load inside the Data Center (UPS+Cooling system , etc..) or its better to segregate the load e.g one ATS for UPS , another one for Cooling system>



    • Tom Mar 30, 2012 @ 3:54

      Your comment,
      “though Mechanical Load does not have to be on the UPS for Tier III”
      was the only portion of your response to Janice that left me confused about your understanding of mechanical loads (induced current) incorporated into a UPS design. Standard industry practice does not place mechanical loads on a UPS source. Maybe you meant to say that mechanical loads within Tier II and Tier III systems incorporate reduntant power supply as well. Static transfer switches can be utilized for this application or a more realistic and cost effective application is a manual transfer switch utilizing a kirk key configuration for safety.
      Further, single corded IT equipment normally does not get “pluged into” STS (static transfer switches) or ATS (automatic transfer switches) single cord components are normally plugged into power power strips that are typcially fed from mutiple power sources such as distribution units (PDU’s) or in some cases the STS is of small size and compatibility that it is located close enough to the load as possible providing power receptacles for small loads such as pc’s.
      Looking forward to your comments on switchgear, tie breaker configuration, control logic and sequencing and generator configuration.

  • Mohammed Smith Oct 11, 2011 @ 20:50

    Sir Scott,
    Kindly do the needful. Answer these brilliant questions of brilliance.

  • D NANDA Dec 28, 2011 @ 18:14

    who will be the certification body for Tier III & Tier IV , Any consultant / Expert can issue the certificate of Tier III & Tier IV
    what are the standards to follow for Tier III & Tier IV certification for data centre
    do you hv any checklist for that

    • Scott Payton Jan 16, 2012 @ 23:46

      Two issues here… There are two “standards” that utilize the term “Tier” as their rating system. Uptime Institute use Tier I – Tier IV (roman numeral) while TIA-942 utilizes Tier 1 – Tier 4 (Arabic numbers).
      There are no certifying bodies for TIA-942. Several companies may claim to do “TIA-942 certification” but this is meaningless. At best they can compare as-built to TIA criteria, and assess that it meets or does not meet in their opinion.
      For Uptime Institute, only Uptime Institute Professional Services can provide an official Certification. This is regardless of the Tier level, so they are the same body to certify a DC as Tier I as Tier III (or any other Tier level).
      Hope that helps.

      • Tarique Jun 6, 2013 @ 17:35

        Can any one help me ,how to contact with uptime for my Tier-III Data Center Certification

  • sun Jan 18, 2012 @ 19:07

    What kind of fiber termination method is using for TIR 3 datacetres.
    Please give me an idea

  • Scott Payton Jan 25, 2012 @ 4:08

    Tier III (or Tier 3) does not specify the type of fiber termination. It’s not part of the Tier standard. There are likely opinions on “best practice” for fiber termination in Tier standards.

    This whole thread seems to be way off topic of UNIX world… I would suggest visiting Tek-Tips (www.tek-tips.com) and join my moderated DC forum there (Data Center Discussion).
    Best regards,

  • BejoyN Feb 1, 2012 @ 15:13

    Hi Scott,

    We are in the process of setting up a data centre in Africa. We are hoping to achieve a Tier III status on this data centre as we will have redudant power supply (Power from the Electricity company Sub Station + 2 x Standby Generators + UPS’s to protect the racks and equipment hosted in the racks), Redundant Data Connectivity (Fibre connectivity + Satelllite for Failover) and Redundant Cooling within the data centre (two cooling units in case of failure). Now iv been reading so many articles online and has proven almost impossible to understand if this actually does meet the Tier III Standard or it will only meet a Tier II.

    I would also like to know how you actually get the certification done once your data centre is built? Is there a specific organisation that you need to contact and they do the assessment and certify accordingly?

    Lastly, regarding the cooling within the data centre. Many have indicated that water based chiller systems are more appropriate but others are dead against water based systems and suggest Gas based systems due to power efficiency especially in countries where the Lime content is high in the water.

    Would be great to get your feedback.



  • Scott Payton Feb 1, 2012 @ 17:44

    Since this thread about DC has gotten “out of hand” on a Unix site, can you please come to Tek-Tips (www.tek-tips.com) and ask these questions in the Data Center Discussion forum? I’m trying to corral all the information into one site, where others can benefit from it.
    Repost there, and I’ll answer all your questions.

  • Raghav Feb 8, 2012 @ 7:06

    Hi Kindly share me the cooling type used in DC.

  • Scott Payton Mar 6, 2012 @ 15:04

    Please direct all DC questions to the “Data Center Discussion” forum on the site http://www.tek-tips.com I’m no longer following this thread here. You can post anonymous on Tek-Tips, or create a login, please.

  • Tommy h Mar 19, 2012 @ 6:11

    Working on a RFP that requests data centers to be as per the Lanyon standard, can anyone advise where I could find more info or what this standard is?

  • Scott Payton Mar 30, 2012 @ 8:00

    The comment about mechanical loads on a UPS is specifically in reference to CRAC units connected to UPS to achieve Tier IV requirement for Continuous Cooling under TS:T. It is HIGHLY advised to provide mechanical load of this type with its own UPS, and not use the same UPS source as the IT gear.
    Regarding single corded equipment, if the rack is fed by multiple PDU which have STS at their sources (PDU also fed by two sources) then in-rack PTS (Point-of-Use Transfer Switch, which can be either STS or ATS) is not necessary. Otherwise, for Tier III and Tier IV under Uptime Institute standard, a localized (in-rack) PTS will suffice. It obviously can’t account for PSU failure in a single device, but at least provides power in the event of loss of a feed (A or B) source.
    Does that clarify?

  • Mark Austin Jul 31, 2012 @ 1:58

    Hi there, Can someone elaborate for me on what is meant by a “single uplink” (as given as part of the definition of a tier 1 data centre installation)? That would be much appreciated, cheers, M.A.

  • Abhijeet Oct 19, 2012 @ 5:10

    I just want to knw about tier 1 and is it belon to Server support and wht is basically the work in server support ? and is there chance of growing urself and how lon u grow in ur career ?

    • Scott Payton Oct 19, 2012 @ 17:56

      You should download the Tier Standard: Topology and Tier Standard: Operational Sustainability from the Uptime Institute web site. It will help you understand what is and is not contained in the Tier rating. Server support has 0 to do with Tier rating. There are many training programs you can enter to improve your DC design and practice capability. DCD, EPI, Uptime Institute, CNet all offer DC programs. Some of them are progressive, others expect you have a certain level of capability and background first.
      Best wishes,

  • Greg Lane Dec 30, 2012 @ 20:34

    Does anyone know a company that can use a project manager with five years of managing data center infrastructure? My experiences are in Tier 4 data centers from fiber optics connectivity to San & storage work. I am located in Atlanta GA.; however, I am open to travel.

  • Vipulkumar Jan 22, 2013 @ 13:12

    How to calculate cooling system requiremend in Data Center?

    • Teja May 27, 2014 @ 18:32

      Hi Vipul,

      here is the simple calculation for Data Center Cooling provisioning.

      1 KW = 3412 BTU (British Thermal Unit)
      for example: u have below racks in ur DC say,
      23 racks of 3 KW
      10 racks of 5 KW

      So total KW is how much, let us calculate here:
      23×3 = 69 KW
      10×5 = 50 KW
      Total is 119 KW.

      119kw x 3412 = 406028

      Now, required Tier will be 406028 / 12000 = 33.83 Ton

      Note: 1Ton = 12000 BTU

      Summary: U need 33.83 Ton of AC requirement for your Data Center.

      You can go for 17Ton x 3 No. (precision AC) here N+1 methodology you can opt.

      17 ton x 2 will be Live / production
      17 ton x 1 will be Redundant (Standby)


  • Chijioke Feb 4, 2013 @ 13:08

    Please what is the advantages of tier 3 data centre over tier 4

    • milica Jul 26, 2013 @ 15:55

      Tier 4 is better than Tier 3. Higher uptime.

      • Scott Payton Jul 27, 2013 @ 3:47

        Compared to what? This has to be put into business context. Return on investment and added complexity of Tier IV often put them at risk of either a) over capitalizing your DC, or b) resulting in MORE down time because complex systems are not thoroughly thought out and tested.

  • Jigar Mar 14, 2013 @ 3:58

    I am Networking guy, I want to know what type of devices has been used in google data center, those are cisco gear or juniper gear or what – (in Networking and security field).
    if someone can provide that info. – that would be greatly appreciated.
    Thanks in advance

  • sathish Feb 6, 2014 @ 10:53

    what is the PUE value for Tier 3 & 2 Data centers

  • hossein Feb 18, 2014 @ 5:40

    سرویس های مراکز داده بر حسب Tier چه هستند؟

    • Vijay Jun 4, 2015 @ 3:26

      No place for tribal language arabic in this forum

  • hossein Feb 18, 2014 @ 5:44

    What are the terms of service data centers Tiers?

    • Scott Payton Feb 18, 2014 @ 6:38

      Please post this question at http://www.tek-tips.com in the forum “Data Center Discussion”. I’m no longer making responses to this thread.

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