Data Center Tier Levels

Your enterprise's old data center has reached the end of the road, and the whole kit and caboodle is moving to a colocation provider. What should you be looking for in the data center, and just how much uptime comes from within?

A lot of the work measuring data center reliability has been done for you. The Uptime Institute's simple data center Tier levels describe what should be provided in terms of overall availability by the particular technical design of a facility.

There are four Uptime Tiers. Each Tier must meet or exceed the capabilities of the previous Tier. Tier I is the simplest and least highly available, and Tier IV is the most complex and most available.

Tier I: Single non-redundant power distribution paths serve IT equipment with non-redundant capacity components, leading to an availability target of 99.671% uptime. Capacity components include items such as uninterruptable power supply, cooling systems and auxiliary generators. Any capacity component failure will result in downtime for a Tier I data center, as will scheduled maintenance.

Tier II: A redundant site infrastructure with redundant capacity components leads to an availability target of 99.741% uptime. The failure of any capacity component can be manually operated by switching over to a redundant item with a short period of downtime, and scheduled maintenance still requires downtime.

Tier III: Multiple independent distribution paths serve IT equipment; there are at least dual power supplies for all IT equipment and the availability target is 99.982% uptime. Planned maintenance can be carried out without downtime. However, a capacity component failure still requires manual switching to a redundant component, which will result in downtime.

Tier IV: All cooling equipment is dual-powered and a completely fault-tolerant architecture leads to an availability target of 99.995% uptime. Planned maintenance and capacity component outages trigger automated switching to redundant components. Downtime should not occur.

In most cases, costs reflect Tiering -- Tier I should be the cheapest, and Tier IV should be the most expensive. But a well-implemented, well-run Tier III or IV facility could have costs that are comparable to a badly run lower-Tier facility.

Watch out for colocation vendors who say their facility is Tier III- or Tier IV-"compliant"; this is meaningless. Quocirca has even seen instances of facility owners saying they are Tier III+ or Tier 3.5. If they want to use the Tier nomenclature, then they should have become certified by the institute.