[CentOS] Temperature sensor

nate centos at linuxpowered.net
Fri Feb 26 19:02:39 UTC 2010


Dominik Zyla wrote:

> You have right. While you checking sensors from few machines, you can
> see the trend. Gotta think about changing the way of temperature  monitoring
> here.

Myself I wouldn't rely on internal equipment sensors to try to
extrapolate ambient temperature from their readings. Most equipment
will automatically spin their fans at faster RPMs as the temperature
goes up which can give false indications of ambient temperature.

I do monitor the temperature of network equipment, but also have
dedicated sensors for ambient readings. Already saved us some pain
once, opened up a new location in London last year and the ambient
temperature at our rack in the data center was 85+ degrees F. The
SLA requires temperature be from 64-78 degrees. Alarms were going off
in Nagios.

The facility claimed there was no issue, and opened up some more
air vents, which didn't help. They still didn't believe us so they
installed their own sensor in our rack. The next day the temperature
dropped by ~10 degrees, I guess they believed their own sensor..

http://portal.aphroland.org/~aphro/rack-temperature.png

People at my own company were questioning the accuracy of this
sensor(there was only one, I prefer 2 but they are cheap bastards),
but I was able to validate the increased temperature by comparing
the internal temp of the switches and load balancers were
significantly higher than other locations. Though even with the
ambient temperature dropping by 10+ degrees, the temperature of
the gear didn't move nearly as much.

The crazy part was I checked the temperature probes at my former
company(different/better data center) and the *exhaust* temperature
of the servers was lower than the *input* temperature from this
new data center. Exhaust temperature was around 78-80 degrees,
several degrees below the 85+.

It seems the facility in London further improved their cooling
in recent weeks as average temperature is down from 78 to about
70-72 now, and is much more stable, prior to the change we
were frequently spiking above 80 and averaging about 78.

Also having ambient temperature sensors can be advantageous in
the event you need to convince a facility they are running too
hot(or out of SLA), as a tech guy myself(as you can probably
see already) I am much less inclined to trust the results of
internal equipment sensors than a standalone external sensor
which can be put on the front of the rack.

nate




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