What is Data Center Tiers?
Data centers are classified based on 'tiers'. Tiers represent the level of service - higher the tier, better will be the level of service.
There are four Tiers, the lowest being Tier I and the highest Tier IV. There could be another tier soon - Tier V - but it is too underdeveloped to be conceptualized in what's left for the decade. Data centers are classified into four tiers - Tier I, Tier II, Tier III, and Tier IV by The Uptime Institute depending on the site infrastructure performance.
Data center Tiers - Tier I
Tier I is what it began with. It is the simplest of data centers and mostly provisioned within the office or at a work desk, typically by assembling components on-site. Tier I may not even have a dedicated server cooling and the office AC might be its only lifeline. However, when procured by a hosting company, Tier I premises are provided with their own power and sometimes a dedicated cooling unit too, but are often without a backup. Without a backup, when the Main goes off, so do servers.
- Tier I data centers have single power and cooling distribution path with no redundant IT components, providing 99.671% availability.
Not many data centers that are left are still Tier I. Most have upgraded and some have shut down.
Data centers - Tier II
- Tier II data centers consist of a single power and cooling distribution path with redundant components, providing 99.741% availability.
Tier II has also been out-phased now but it was once all the hype. Tier I had too many problems than could be ignored. The network was highly unstable and underwent massive downtime, websites complained of slow loading speed. What's left of Tier I was plundered by frequent power outages that caused unbearably long data outages, which in some cases spanned days and in some cases weeks.
Some providers made arrangements to supply uninterrupted power to the data center, and that was all it took to make it Tier II. Not to forget, small arrangements like these can make a significant difference in a system teeming with faults, and so it did with Tier II. Tier II data centers became an instant hit.
Data centers Tier III
- Tier III data centers have two active power and cooling distribution paths with redundant components, providing 99.982% availability.
As time went by, Tier II became the norm. The technology did not change much in the following years. One breakthrough, however, happened.
Until then whenever the main power went off, someone within the data center had to manually turn on the cloud backup generator, which took several minutes to run at its full throttle. In the interim period when Main was off and the generator had not yet started delivering power, there would be a few minutes of blackout. During the blackout period, websites would go down temporarily and return back to the functioning state as soon as the backup power kicked in.
By the time Tier III was announced, hosting providers had found out the solution to this overbearing problem. In what we can call a very smart move, the power lines were so laid that both backup and Main lines were always alive. When the main power went off, the backup filled in and supplied power, and with main power available, the backup remained on standby.
Tier IV data centers
Tier IV datacenters are more or less like Tier III. They both have dual power and redundant systems. What makes Tier IV a 'Tier IV' is its capability to continue running, even when one of the components has failed. The fourth tier is completely redundant i.e. it has a backup for every component.
- Tier IV data centers are fully fault-tolerant with multiple power and cooling distribution paths, providing 99.995% availability.
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