What are data center availability modes - Article 1

Data center availability modes defines the availability of physical infrastructure in case of any failure. It’s quite obvious that some machines may get damage/stop working unexpectedly due to some unexpected incidents. Have you ever thought what will be the impact when this happens to a data center? Well as a computer engineer I would say that I will never imaging it incident since the impact can be nothing but stopping an entire business or partial business that are run on data center. In some instances machine damages can’t be predicted or controlled completely by humans. The best thing that we can do to avoid down time is to minimize the maximum risk factor by having multiple backup plans. Here is what the importance of data center availability modes which are the general standards to avoid any down time.

We will discuss the general standards followed by various data centers to avoid the challenges that may happen to physical infrastructure.

·     Uptime Institute Tiers (I-IV)

·     EN 50600 Availability classes (1-4)

·     TIA 942-B Ratings (1-4)

·     10 Syska Hennessy Criticality Levels

·     ANSI/BICSI Classes (F0-F4)

·     Others: N, N+1, 2N, 2(N+1)

Based on any one of the above data center standards, your DC design and operation will vary. 

Uptime Institute Tiers (I-IV)

Uptime Institute is the IT industry’s most trusted and adopted global standard for the proper design, build and operation of data centers. They evaluate data center infrastructure based on certain criteria and DC availability will be certified as per that. The Tier Classification System provides the data center industry with a consistent method to compare typically unique, customized facilities based on expected site infrastructure performance, or uptime. 

Uptime institute tier levels are mainly evaluated for 3 categories of a data center facility and namely Tier Certification Design Documents (TCDD), Tier Certification Constructed Facility (TCCF), Tier Certification Operational Sustainability (TCOS). Below are the various data center standards categorized by Uptime institute. 

Tier 1: A Tier 1 data centre have no redundant capacity components (single uplink and servers). It has an expected uptime of 99.671% (28.8 hours of downtime annually).

Tier 2: A Tier 2 data centre has a single path for power and cooling and some redundant and backup components. It has an expected uptime of 99.741% (22 hours of downtime annually).

Tier 3: A Tier 3 data centre has multiple paths for power, cooling and systems in place to update and maintain it without taking it offline. It has an expected uptime of 99.982% (1.6 hours of downtime annually). These data centers provides N+1 fault tolerant providing at least 72-hour power outage protection. This is the most adapted Tier levels that you can see throughout the world.

Tier 4: A Tier 4 data centre is built to be completely fault tolerant and has redundancy for every component including uplinks, storage, chillers, HVAC systems, servers etc. Everything is dual-powered. These data centers are 2N+1 fully redundant infrastructure. It has an expected uptime of 99.995% (26.3 minutes of downtime annually).

Have you noticed the letter ‘N’which is indicating the redundancy capability of data centers. Ever wonder what does it mean? 

Nis simply the amount required for operation. It represents the capacity that you need to operate. There is no backup system so if the system fails, it fails and downtime is the ultimate result. If you have a flat tire and no spare, you have N.

N+1represents the amount required for operation plus a backup. It ensures system availability even in the event of a component failure. It is similar to the concept of a spare time on your car. When you get a flat, you have the ability to swap out the flat with a spare tire. This simply means that you could survive one flat tire.

2N+1means that you have two times the amount required for operation plus a backup. This means that you have a full size spare tire plus a temporary spare tire just in case. That means that you could incur two flat tires and still operate.

Typically the uptime institute certifications will look like below,

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