Energy usage is a focus for many at the moment. For IT, it seems to be a big focus - mainly
as organisations become more aware of how much energy is wasted in their data
centre facilities. However, it is likely
to be brought into even greater focus in the not so far distant future, as the
looming energy deficit starts to become more apparent.
A mix of short-sightedness and prevarication by politicians
means that the UK is now at a position where it is unlikely that it will be
able to meet all its consumers' energy needs in just a few years - the UK's energy
market overseer, Ofgem predicts that the UK's current energy generation
over-capacity of 14% could fall to 4% in just 3 years. The failure, or the need to take down for
even planned maintenance - of only one generation plant could lead to
insufficient power being available for all the country's needs.
Therefore, planned outages will be required to be put in
place - and the biggest energy users will be targeted where overall country
needs will not be adversely impacted.
So - steel and aluminium production is unlikely to be
hit. Retail may be asked to cut down on
lighting and heating. But the one place
where politicians can really point to is the use of IT - and how many organisations
could be asked to reduce their energy usage here - or risk having it cut off
for periods of time.
It is widely accepted that data centres are inefficient when
it comes to usage of energy - the average utilisation of a server is around
10-20% of cpu, and of storage around 30%.
Sure - a move to virtualisation can drive up these utilisation rates and
so lower the amount of equipment being used and so lower the energy being
needed - but is this the best way to address the overall need?
To take a bigger picture, it is necessary to look at the
whole data centre facility and its energy usage. There is a means of gaining a measure of the
overall energy efficiency of a facility through the use of power usage
effectiveness, PUE. This is a comparison
of the total amount of energy used by a facility divided by the amount that is
used to power the IT workloads - i.e. that used by servers, storage and network
equipment. The rest of the energy is
used in peripheral areas, such as lighting, cooling, and uninterruptable power
supplies (UPSs).
A theoretical perfect data centre should therefore have a
PUE of 1 - all the energy is used in powering IT workloads. However, in practice, the PUE for an
"average" facility is around 2.0 - for each Watt of power used for IT workloads,
another Watt is used for peripheral items.
So - only 50% of the facility's total energy is reaching the
servers, storage and networking equipment.
Running at 20% IT equipment utilisation means that at a rough estimate,
around 90% of a facility's total energy input is essentially going to
waste. Upping IT equipment utilisation
rates to 40% and getting rid of excess equipment could mean a saving 10% of a
data centre's energy usage - which is wonderful - but still only means that 20%
of a data centre's energy is being used for useful IT work.
However, the majority of data centres utilise UPSs to
support pretty much all the energy used across the facility. Unfortunately, many of these devices are
pretty old, and will be running at 94% efficiency or less. Modern UPSs run at 98% efficiency or
greater. But, is a 4% improvement in
energy efficiency at a UPS worth the bother when a 10% improvement at the
server and storage layers is possible?
Back to the maths. If
all the facility's energy goes through the UPS, then a 4% improvement across all
systems (servers, storage, networking, cooling, lighting) is a 4% savings in
energy bill - without having changed anything but the UPS. Now, introduce the virtualisation mentioned
above. The server utilisation rates are
upped from 20% to 40% as before, and the saving is 10% of the data centre's
energy bill. But, because we have
improved the overall data centre's energy usage as well, we get a greater
saving. Every time we improve the
equipment in the data centre - IT or support - then we gain that extra energy
efficiency as well.
Modern UPSs also provide a host of other capabilities - as
battery technology and battery management systems have improved, a
well-implemented UPS can help in bridging some breaks in energy provision
without the need for auxiliary generators to switch in. They can also better deal with low voltage
situations ("brown outs"), ensuring that an optimised energy feed gets to all
equipment.
Should Ofgem be right, there will be planned brown outs and
power cuts around the country within a few years. Organisations can help in many ways -
improving their data centres so that they are more energy efficient could put
this back by a few months. However,
ensuring that their data centre facilities have newer, more effective UPSs in
place can help in not only providing a far more energy efficient facility, but
also in dealing with the problems that an energy deficit could present.
Quocirca has written a report on the subject, which can be
downloaded for free here: http://quocirca.com/reports/773/powering-the-data-centre
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