Insufficient power and excessive heat are the two
biggest issues IT directors face when running a datacentre,
according to a survey of 112 users by analyst firm
Gartner.
Discussing his experience of deploying blade servers in a
datacentre, Owen Williams, head of IT at property firm Knight
Frank, said, "When installing blade servers, watch out for blade
cabinets, which draw more power than the older cabinets, and the
blades throw out a lot of heat - you may need to upgrade your air
conditioning."
He said this was because older racks draw cold air in from the
bottom and blow hot air out from the top. Blade racks, on the other
hand, draw air in from the front and blow it out of the back.
"You need grilled floor tiles in front of the racks to blow cold
air in the right location and you need to arrange your racks back
to back so that hot air from the back of each rack is drawn up and
chilled by your air conditioning units," Williams said. Such a
set-up avoids hot air from one rack being blown into the front of
the rack behind.
Gartner analyst Andy Butler said, "The chief cooling challenge of
blades so far has been the ability to cram the technology in such a
way that the density promises can be achieved."
He said suppliers routinely had to leave "fresh air" inside rack
configurations to allow enough space in the cabinet for the
technology to work reliably.
"I also see suppliers putting great effort into designing racks and
cabinets in a way that will pass the air through the blades and
fans more effectively," Butler added.
Even if it were possible to cram a full complement of blades into a
single rack, the power demands of such a configuration would be
significant, Butler said.
Tim Dougherty (pictured above with eServer Bladecenters), IBM
eServer Bladecenter worldwide manager, said IBM offers a thermal
design in its blade servers called calibrated vectored cooling. He
said this uses energy-efficient blowers that move air from the
front of the system to the back while protecting components inside
the server.
John King, enterprise server manager at Hewlett-Packard, said
raising the floor in datacentres could reduce heat by 20%.
King said a single rack of blade servers would need to be split
into two or more racks to overcome power distribution issues. This
reduces the amount of power required for each rack, but adds to
demands on space.
HP's System Insight Manager server management utility can be used
with servers running Intel Speedstep technology to reduce the speed
of the processor, which lowers power consumption and radiated heat.
"The next step is to control thermal dynamics automatically so the
processor can be slowed down based on temperature," said
King.
The company is also working with software partners to model the
thermal dynamics of datacentres, King added.
HP has seen growing interest among UK IT directors in the thermal
dynamics of blades and power consumption. In February, a group of
HP engineers presented papers on these topics at three seminars:
two in London and one in Manchester.
The impact of cooling demands on datacentre
design
Evidence is growing that datacentres are being over-designed for
electrical capacity, because of concerns about meeting the
incremental power and cooling demands of modern server equipment
(such as blade servers), according to Gartner.
The analyst firm said sufficient capacity should be delivered
relative to patch panels, conduits and intermediate distribution
feeds. Special attention should be focused on equipment densities
relative to initial and longer-term electrical power
capacities.
The company said the single greatest issue in the contemporary
datacentre is maintaining adequate cooling and air movement, given
the intense heat gain of modern blade server and direct-access
storage device equipment.
Modern blade servers can be packed into a single-rack enclosure,
resulting in power demands of 18 to 20 kilowatts per rack,
according to Gartner.
The primary issue with dense-packing the layout with
high-capacity servers is that, although it is efficient from a
space standpoint, it creates serious heat problems requiring
incremental cooling, as well as significant incremental electrical
costs.
As a general rule, Gartner advised users to plan for the
datacentre to scale from 50 watts to 100 watts per square foot (in
a raised floor area); increase capacity on a modular basis, and
assess the trade-offs between space and power in the total cost of
the new facility. It said users should also provide space between
racks for air circulation.
Gartner said electrical capacity ranging from 30 watts to 70
watts per square foot for computer equipment is typically required.
However, additional power is required for air conditioning,
humidification, lighting, and uninterruptible power supply and
transformer losses.
This additional demand could add one to one-and-a-half times
more wattage to the electrical load, depending on equipment spacing
and air-handling efficiencies.