Tier I, Tier II, Tier III or Tier IV Data Centers: What’s the Difference?

by Data Holdings

There is a great deal of confusion and misinformation regarding what constitutes data center tiers, how they differ from each other, and why it matters. This article will attempt to clear up that confusion and provide insight into what matters when selecting a data center for colocation or data center managed services.

The Uptime Institute first published criteria for data center tiers in the 1990s. The data center industry has matured significantly since then, but the same basic criteria hold true and have become the accepted industry standards.

A Tier IV data center is the pinnacle of the industry by being fully “fault tolerant.” This means that every system, be it mechanical or electrical, is backed up to a factor of three, described in industry terminology as 2N (Need x 2). In practical terms, if a first system fails, there is a backup, and then there is a second backup ready to assume the need if required. There are very few multi-tenant Tier IV data centers due to the extremely high cost of construction and maintenance.

Tier III data centers are described as being “concurrently maintainable,” or in industry terminology as N+1 (Need plus 1). The entire data center has redundant systems to allow for temporary disabling of all systems (mechanical and electrical) for maintenance or in case of failure. Relatively few data centers are truly of Tier III caliber. Most have redundancy in some systems, but not others. Some multi-tenant operators claim Tier III data center status, but in reality, are Tier II, perhaps with limited Tier III features.

Tier II data centers have some redundant infrastructure components. Some systems can be termed N+1 but not all. The majority of multi-tenant data centers fall into this category.

Tier I facilities have basic infrastructure with no redundancy and are rarely acceptable for hosting third-party applications.

Additionally, the industry (but not the Uptime Institute) recognizes a hybrid category of data centers, notably between a Tier III Data Center and a Tier IV. These facilities are Tier III+ with some Tier III (N+1) elements, and some Tier IV (2N) elements. The 2N elements typically focus on redundant utility power sources, generators and electrical delivery systems.

Significantly, there are common data center design shortcomings that contribute to gray areas where a facility claims to be a higher tier than it actually is, but probably restrict it back to a lower practical tier. Such omissions include:

  • Not building to a higher tier design. Some data centers are designed to be Tier III but for budgetary reasons construction falls short of the design.
  • Insufficient grounding. Proper grounding is essential to the uptime of applications and equipment performance, in addition to contributing to avoidable fire risk.
  • Utilizing a non-purpose-built facility. For example, an office building or a factory converted to be a data center simply does not have requisite physical design elements of a hardened facility.
  • A facility with windows on or near the data center floor, or a metal pan roof. Both factors contribute to significant risk in severe weather situations such as tornadoes or hurricanes.
  • An outdoor generator with inadequate fencing. If a fence is easily hurdled the generator is vulnerable to vandalism or malicious damage, endangering operations.
  • Ability to avoid security scrutiny upon entry to the building. Every aspect of a data center must be filmed and the data kept for a minimum of 90 days to abide by compliance requirements.

When choosing a data center, rather than listening to a sales person’s assurances and impressive literature, a strong indicator of operator integrity is the commitment to apply for and submit to SSAE16 SOC II, Type 2 audit. The SSAE16 audit is based on internal controls over financial reporting, a SOC II report evaluates an organization’s information systems that are relevant to security, availability, processing integrity, confidentiality or privacy, while the Type 2 classification denotes that such conditions have remained consistent for a period of at least 6 months.

If a facility operator does not submit to achieve such industry qualifications, which are very beneficial to their business, it is worth asking the question “why not?” At very least it would start an interesting conversation.

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