It’s a common question for anyone running servers – where should you put temperature and humidity sensors?
The first step is to decide if you want to monitor server temperature and humidity conditions within each of the individual racks or monitor the ambient room conditions. Both approaches will generate information that can be used to provide accurate insight into environmental conditions and warnings in the event of air conditioning failure. However, it’s worth remembering that the in-rack and in-room conditions can be very different.
In-rack sensor placement
In-house experiments conducted by Jacarta show the temperature within a single rack (in a non-temperature controlled environment) may vary by as much as 9.5°C, with the top of the rack being the hottest and the bottom the coolest. In instances like this, you may choose to place your temperature sensor at the top of the rack to provide a ‘worst case’ reading, or you could install the sensor in the middle to provide an average reading.
It’s also important to know how air moves throughout your rack. This will depend on your specific rack and cooling setup. Unless you specifically want to monitor the temperature of the cool air entering (or the warm air exiting) your racks, it is best practice to avoid direct airflow over temperature and humidity sensors. Direct airflow over the sensor chip can cause false readings for both the temperature and humidity and values tend to fluctuate more in these positions, causing false and/or frequent alarms.
To provide the highest level of protection, multiple sensors can be placed around a rack, with different alarm thresholds set for each location to provide you with a definitive map of in-rack conditions. In some instances, it may be beneficial to locate a sensor adjacent to hardware that is susceptible to temperature or humidity fluctuations.
In-room sensor placement
There is a similar range of considerations if you place the sensors outside the rack to measure in-room conditions. Again, it’s important to avoid direct airflow, and depending on the location, you may also need to avoid direct sunlight or other environmental factors, such as doors that are frequently opened and closed.
In these situations, it may be useful to trial different locations over set periods of time to see which locations provide you with a reliable and stable reading that is also sensitive enough to changing conditions in order to provide an alert should thresholds be breached.
Temperature and humidity thresholds
The thresholds you choose will depend on your setup. You may wish to follow recognised guidelines such as those provided by ASHRAE. ASHRAE recommends an operating temperature of 18-32°C and humidity of 40-60%, though other bodies recommend both smaller and larger operating ranges!
While these temperatures are, of course, optimal, they can be difficult to maintain in some circumstances. You could consider running your sensors in situ for a few days, note the typical peaks and troughs, and then set your thresholds around these.
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Article courtesy of Jacarta.
