What are data center availability modes- Article 3

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10 Syska Hennessy Criticality Levels

ENR has ranked Syska Hennessy Group as one of the world’s top five in data-center engineering design for the last ten years. Syska’s Critical- ity Level concept is comparable in parts to data center “tier” levels used in the industry. These criticality or tier levels differentiate expected availability and reliability between sites that are designed, constructed, commissioned, maintained, and operated at different budget and priority levels. Whereas many earlier published tier classifications focused on power to the critical load, Syska’s Criticality Levels address everything that is important for availability of a critical facility. The best way to understand these 10 levels of standard is to compare with the uptime institutes tier levels. Let us understand that as below when comparing,

Syska Criticality	Uptime institute	Estimated % of availability	Expected Annual down time.
C1	Tier 1	98	20–40 hours
C2	Tier 2	99	10–25 hours
C3	Tier 3	99.9	1-15 hours
C4	Tier 4	99.99	0.25–1 hours
C5		99.999	1–20 minutes
C6		99.9999	1–15 hours
C7		99.99999
C8		99.999999
C9		99.9999999
C10		99.99999999

If you would like to understand more about Syska Hennessy standards read through here

PS: ENR specified on above notes is denoted for Engineering News-Record which is an American weekly magazine that provides news, analysis, data and opinion for the construction industry worldwide.

ANSI/BICSI Classes (F0-F4)

BICSI 002-2019 (Building Industry Consulting Service International) standard is written to be used as a standard for Data Centre Design and Implementation. Written by industry professionals from all major disciplines, this standard not only lists what a data center requires, but also provides ample recommendations on the best methods of implementing a design to fulfill your specific needs. These standards are used in conjunction with other multiple standards or publications such as ,

– TIA: 942, 568C, 569B,

– ISO/IEC:11801, 24764

– CENELEC: EN 50173, 50174

– NFPA: 70 (NEC®), 75

– ASHRAE: Datacom and Data Centre

– IEEE: 493, 1100 (Gold and Emerald Books) – EN 50600

There are 5 availability classes defined as per BICSI 002-2019 and those can be defined as below,

Availability Class 0 :The objective of Class 0 is to support the basic requirements of the IT functions without supplementary equipment. Capital cost avoidance is the major driver. There is a high risk of downtime because of planned and unplanned events.

Availability Class 1 :The objective of Class 1 is to support the basic requirements of the IT functions. There is a high risk of downtime because of planned and unplanned events. However, in Class 1 data centers, remedial maintenance can be performed during nonscheduled hours.

Availability Class 2 : The objective of Class 2 is to provide a level of reliability higher than that defined in Class 1 to reduce the risk of downtime because of component failure. In Class 2 data centers, there is a moderate risk of downtime as a result of planned and unplanned events. Maintenance activities can typically be performed during unscheduled hours.

Availability Class 3 : The objective of Class 3 is to provide additional reliability and maintainability to reduce the risk of downtime because of natural disasters, human-driven disasters, planned maintenance, and repair activities. Maintenance and repair activities will typically need to be performed during full production time with no opportunity for curtailed operations.

Availability Class 4 : The objective of Class 4 is to eliminate downtime through the application of all tactics to provide continuous operation regardless of planned or unplanned activities. All recognizable single points of failure are eliminated.

Below table is the simple representation of these fictional availability classes,

If you would like to understand more about BICSI Classesread through here 

Others: N, N+1, 2N, 2(N+1)

After all, the above are international standards that can be followed to achieve the highest redundancy and reliability for a data center infrastructure. These standard certifications are the proof to our clients that the facility achievements that you are following. The periodic auditing from certification authority will make sure that your facilities are most efficient on a frequent interval too. But what is the case when you want to  have your own small data centers that doesn’t required someone else surety for your facility? You have literally a small scale data center? Yes you can have this(the least case scenario that it will be followed on these days). 

All that you need is to have your own physical infrastructure(mainly power, cooling and connectivity)  that can be defined in terms of N, N+1, 2N, 2N+1, 2(N+1).

Concept is same as the things that we discussed in uptime institute Tier levels.

Nis simply the amount required for operation. For instance, a data center server may require one power supply operating at specific power ratings to keep the server running at optimal availability conditions.

N+Xrefers to a redundant system that contains X number of spare components to act as an independent backup when the appropriate component fails to operate as intended. N+1means that only one backup component is available to complementing the N original component(s). N+2means that two backup components are available to ensure additional resilience.

2Nmeans that you have two times the amount required for operation. You have two units of equal size, capabilities, and capacity. 2N+1means that you have two times the amount required for operation plus a backup.

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