Erik Trimble wrote:
Neal Pollack wrote:
On 07/ 1/09 05:11 AM, Haudy Kazemi wrote:
Ian Collins wrote:
Or run your systems of DC and get as much backup as you have room
(and budget!) for batteries. I once visited a central exchange
with 48 hours of battery capacity...
The way Google handles UPSes is to have a small 12v battery
integrated with each PC power supply. When the machine is on, the
battery has its charged maintained. Not unlike a laptop in that it
has a built in battery backup, but using an inexpensive sealed lead
acid battery instead of lithium ion. Here is info along with photos
of the Google server internals:
http://news.cnet.com/8301-1001_3-10209580-92.html
http://willysr.blogspot.com/2009/04/googles-server-design.html
which is of course why people claim that google is less green than
detroit :-)
Each sealed lead-acid battery is good for about 2 years in those
power supplies.
Goodle uses more than 10,000 servers, many more.
Do the math. That's many many tons of lead and acid in the dump
every 24 months.....
Yes, but...
Lead acid batteries are one of (if not _the_) the most-recycled items
in the world. Something like 99.99% of all lead-acid batteries get
fully recycled.
Lead acid batteries are one of the most recycled items, both because it
makes economic sense and because it is a legal requirement. According
to Google's published results, they are also have some of the most power
efficient systems out there with 90%+ efficient 12v power supplies and
great Power Usage Efficiency (PUE) numbers:
http://www.greenm3.com/2009/04/insights-into-googles-pue-a-laptop-approach-to-power-supplies-and-ups-for-servers-achieves-999-efficient-ups-system.html
I'm not convinced by the argument that Google is less green than
Detroit, and from the smiley it appears this statement was meant as
tongue-in-cheek humor.
Personally, I don't like Google's solution. That's waaaay too many
small batteries in everything. I'd be more in favor of something like
a double marine battery every 2 racks. Lots more power, and those
things are far easier to recondition and reuse - and much less labor
intensive to install than 1 battery in 80+ servers.
With a good quality lead acid battery and appropriate charge management
system, the battery can last the business life of the server without
replacement (e.g. 4 years). In that case the batteries could be
considered 'hands off' and would be replaced as a single unit along with
the server. Google has talked about using commodity hardware vs.
traditional server equipment, and here it looks like they have
similar-to-commodity hardware optimized for efficiency via their
leveraging of purchasing power (i.e. custom power supplies and OEM
Gigabyte motherboards).
The experience people have with lead acid UPS batteries (and lithium
phone and laptop batteries for that matter) dying in 2 years is
primarily a function of poor quality batteries and/or poorly designed
chargers that trickle charge the batteries to death. (Margins on
official replacement batteries for UPSes, laptops and phones are high,
leaving room in the market for refilled batteries and third party
equivalents. There isn't much of an incentive to design in a good
charging system.) The electric vehicle community knows this well and
makes sure to use good charging and balancing systems to get their
batteries to last for hundreds to thousands of cycles over several years
(UPS systems don't need to cycle very often, but they do need deep cycle
discharge capability). Some DIY electric vehicle enthusiasts
successfully use batteries that in a former life served in UPSes but
were revived. More on lead acid charging and care:
Charging Basics: http://www.evdl.org/pages/hartcharge.html
Care Basics: http://www.evdl.org/pages/hartbatt.html
All this said, I certainly do agree that the proper thing to do is
move to full 12V DC inputs for all computers intended for data center
use. Eliminating the need for non-12V (i.e. get rid of all the stuff
that want 5V) on the internal components is really needed to make this
efficient; that way, all you need in the way of a power supply is
something that takes 48VDC input, and breaks up the leads into 12V
outputs. Really cheap, really efficient. Having a nice 48VDC bus for
the rack (like Telco) is much more energy efficient and far easier to
hook something like a small UPS to...
I think it will be hard for 48v in 12v out DC/DC converters to compete
in price and efficiency with a 240v AC input 12v DC out power supply
that is 90%+ efficient (a quick Google search for 'power supply 95%
efficient' finds models as well). 48v DC buses and batteries still need
to be fed from a power supply of their own. Google's approach seems
reasonable, assuming they have integrated a good battery
charger/maintainer and are running off 240v AC.
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