require cooling and humidity control, whichmay dictateits location within the building.Also consider whether the UPS can be forced to trickle-charge its batteries rather than to charge them as quickly as it can. A UPS fast- charging batteries, puts a huge load on the rest of the power system, which may bring the power down.With trickle-charging, amuch lower additional loadis placed on the rest of the power system.
Generators have to be carefullymaintained, testedmonthly, and periodi- cally refueled.Otherwise, they will not work on the few occasions when they are needed, and you will have wasted yourmoney.
If a data center has a generator, the HVAC systemalsomust be on pro- tected power.Otherwise, the systems will overheat.
Case Study: A Failing HVAC System
A small start-up biotechnology company of about 50 people was building its first data center, having just moved into a large building where it was planning to stay in for at least 10 years. The company did not have a senior SA on staff. The facilities man- ager didn’t realize how much heat a data center can generate and decided to save some money on the HVAC system by getting a less powerful one than recommended by the data center contractors. Instead, the company went with the unit recom- mended by the HVAC salesperson, who apparently was not familiar with data center planning.
A few years later, the data center was full of equipment, and the HVAC system was failing every few months. Each time this happened, the SAs shut down the less essential machines, got huge buckets of ice (which the labs had lots of) and fans, and tried to keep the most critical parts of the data center running for the rest of the day. The SAs then shut everything off overnight. Over the following 2 or 3 weeks, a multitude of hardware failures, mostly disks, occurred. Then things would even out for a while until the next HVAC failure. The HVAC engineers told the SAs the problem was that the unit was unable to keep up with the amount of heat the room was generating.
The problem persisted until additional cooling capacity was installed.
Heat sensors distributed around the data center and connected to the monitoring systemare useful for detecting hot spots.A quick, cheap alterna- tiveis to move digital thermometers that record the high and low tempera- tures around the room.If you are good atjudging temperatures, you can also check for hot spots with your hand.Hot spots with no airflow are particu- larly problematic because they will get hotter faster.When there are known hot spots, the problemcan be addressed bymoving equipment or altering the HVAC system.If hot spots go unnoticed, they can be the source of equipment failure.Some hardware vendors provide a way to monitor the temperature at one or more points inside their equipment. If this feature is provided, it should be used because doing so can provide better coverage than deploying heat sensors.
HVAC systems often fail silently and sometimes return to service without anyone noticing.Because HVAC failures cause hardware to failmore quickly, it is important to notice when the HVAC system fails.If an HVAC system itself does not provide amonitoringmechanismthat can automatically alert the helpdesk systems, the network-monitoring systems should be configured tomonitor heat sensors.
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