Know your data center monitoring system

You can't depend on a building system to run the data center. Implement a BMS and a DCIM tool to monitor and predict system changes, tighten security and more.

Data center monitoring systems are critical for managing a facility. Knowing whether you need a BMS or a DCIM system -- or both -- is half the battle.

Nearly every building today, new and old, has a building management or automation system (BMS or BAS) to monitor the major power, cooling and lighting systems. Building management systems are robust, comprised of standardized software platforms and communications protocols.

A BMS monitors and controls the total building infrastructure, primarily those systems that use the most energy. For example, the BMS senses temperatures on each floor -- sometimes in every room -- and adjusts the heating and cooling output as necessary.

The BMS usually monitors all the equipment in the central utility plant: chillers, air handlers, cooling towers, pumps, water temperatures and flow rates and power draws. Automation systems shut off lights at night, control window shades as the sun angle changes, and track and react to several other conditions. Regardless of control sophistication, the BMS' most important function is to raise alarms if something goes out of pre-set limits or fails.

Are these the same things we want from our DCIM?

There is no single standard of data center infrastructure management (DCIM); it can be as simple as a monitor on cabinet power strips, or as sophisticated as a granular, all-inclusive data center monitoring system.

The BMS is a facilities tool that also deals with systems, so why do we need a separate DCIM system as well? DCIM provides more detailed information than BMS, and helps the data center manager run the wide range of critical systems under their care.

DCIM and BMS are not mutually exclusive; they should be complimentary. Some equipment in the data center should be monitored by the BMS. When choosing a DCIM tool, ensure it can interface with the BMS.


There are three fundamental differences between BMS and DCIM.

BMS monitors major parameters of major systems, and raises alarms if something fails. Although you can see trends that portend a problem, predictive analysis is not BMS' purpose.

If the building air conditioning fails, it's uncomfortable, but if the data center air conditioning fails, it's catastrophic. That's one example of why DCIM provides trend information and the monitoring data to invoke preventive maintenance before something critical fails. Prediction requires the accumulation, storage and analysis of an enormous amount of data -- data that would overwhelm a BMS. Turning the mass of data from all the monitored devices into useful information can prevent a serious crash.

The BMS uses different connectivity protocols than IT. Most common to BMS are DeviceNet, XML, BACnet, LonWorks and Modbus, whereas IT uses mainly Internet Protocol (IP). Monitoring the data center with BMS would require the system to have a communications interface or adapter for every IP connection.

Data center devices handle large quantities of data points -- often the common binary number of 256. The cumulative input from every device in the facility would overwhelm a BMS in terms of both data point interfaces and data reduction and analysis tasks. DCIM software accumulates those thousands of pieces of information from IP-based data streams and distills them into usable information.

Only major alarms and primary data should be segmented by DCIM and re-transmitted to the BMS. The rest is of little use in running the building.

DCIM will do many things a BMS won't

DCIM is an evolving field, and not every DCIM product does all of these things, but these are the general areas DCIM handles and BMS products do not:

Electrical phase balancing: The output of every large uninterruptible power supply (UPS), as well as the branch circuit distribution to many data center cabinets, is three-phase. In order to realize maximum capacity from each circuit and the UPS, equalize the current draws on each phase.  All UPS systems -- and many power distribution units (ePDUs, iPDUs, CDUs, etc.) -- have built-in monitoring, but it's inefficient to run from cabinet-to-cabinet and device-to-device to balance power.

If the data center uses "smart" PDUs with IP-addressable interfaces, the data center monitoring system can track the power draws on each phase in each cabinet, as well as at each juncture in the power chain. Users can calculate a balanced scheme before making actual power changes in cabinets. The BMS looks only at the incoming power to the UPS, which is insufficient for this important and ongoing task.

Rack and cabinet temperature/humidity monitoring: The BMS monitors some representative point in the room and alarms if this point hits a significant out-of-range condition, but that's not enough for a good monitoring system in the data center. Temperatures vary significantly from the top to bottom of a cabinet and across the breadth of a facility. With higher inlet temperatures and denser cabinets becoming the norm, comprehensive temperature information matters when deciding where to install a new piece of equipment, or during an air conditioner maintenance or failure period. 

Most "smart" PDUs have temperature and humidity probe accessories to monitor critical points on cabinets and in the room via the same IP port that transmits power use. Even minimal DCIM packages can turn this additional data load into useful information.

Cabinet security: The building security system -- tied into the BMS or not -- observes data center entry and exit, but rarely anything else. It is becoming more common for data centers to house equipment from different owners, such as in colocation facilities, or to have cabinets with restricted access and equip those cabinets with cipher locks. Remote-monitored locks are available, and many can be connected through intelligent power strips. A DCIM tool can be configured to track security information so only the data center manager or other authorized parties access it.

Inventory control:  Some of the more robust DCIM software packages track IT hardware -- sometimes with the help of radio frequency identification tags. This is useful in a large facility where assets are regularly added, replaced and moved.

About the author: 
Robert McFarlane is a principal in charge of data center design at Shen Milsom and Wilke LLC, with more than 35 years of experience. An expert in data center power and cooling, he helped pioneer building cable design and is a corresponding member of ASHRAE TC9.9. McFarlane also teaches at Marist College's Institute for Data Center Professionals.

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