High Density Data Center Monitoring - Verification and Auditing in the Data Centre
Data equipment presents a set of unique challenges to your heating and cooling installation. Older measurement methods and recommendations, such as Telcordia GR-63-CORE, were not designed with computer equipment in mind and modern high density blade servers and rack mount equipment is best monitored using a different approach. This document describes how to achieve accurate measurements for data racks of various sizes and complexity.
Accurate measurements require a high density of sensors. The publication ASHRAE Thermal Guidelines for Data Processing Environments, Second Edition 2009, contains specific advice and recommendations for data equipment.
What are the limits?
Modern data equipment will operate reliably over a wide range of temperatures and humidity. ASHRAE specifies that the Temperature should be between 18C and 27C, a higher limit than in many older specifications, and Humidity should be in the range 20 to 80% RH. Most datacentres have fairly consistent humidity levels, it is unusual to find big fluctuations. Temperature fluctuations by poor placement of equipment and inadequate or misdirected airflows are more common and can result in localised 'hot spots'.
Where to measure?
The locations of the measuring points will depend on the size of the rack to be measured, but in general you should arrange the sensors in a regular grid pattern. For racks with doors it is normal to operate them with the doors closed and if this is the case then measurements should be taken with the doors shut. All measurements should be taken for the air INTAKE side of the rack.
1. Small Racks, height 1U to 3U
If your servers take up 1U of space, locate sensors at the geometric centre of the rack and one each end spaced equally. The sensors should be 50mm (2in) from the equipment front. For racks of up to 3U in height locate the sensors in a line along the centre.
2. Medium Rack, height 4U to 6U
For a larger rack the basic principle is the same, though you will need more sensors. Again these are placed on the air intake side, 50mm (2in) from the equipment front.
3.Large racks, 7U and larger
As before the aim is to arrange the sensors in a regular grid pattern, on the air intake side, 50mm (2in) from the equipment front.
If you have a rack of 20 devices in a single vertical stack measure at the top centre, the middle centre and the bottom centre.
All readings should fall within the acceptable limits. If any are outside the range then further investigation should be undertaken to find the cause of the problem and resolve it. Some issues may be relatively simple to resolve, airflow may be redirected by using blanking plates or repositioning equipment, while more serious problems may require a redesign of the room layout.