Tuesday Aug 21, 2007
Truly being Eco is about looking at the right things and highlighting
them in a way so you can make real judgments that really make a difference.
A fellow Sun employee gave me a great analogy, if you want to save
power switch off the light! Obvious. But too often we try to
use fancy technology to save energy when proper policy is more important.
If you leave incandescent lights on all day, switching to CFL
(compact florescent lights = better technology) can save energy.
but if you "switch it off during the daylight hours" (better policy) you
can save a lot more.
How does this apply to datacenters? Everyone needs to change
their policies to operate servers at not an insane 20-30% utilisation
but to 50% or more.
There are all kinds of virtualisation technologies that can be used
if for some reason you can't simply drive up the load. Take two
servers at 25% and consolidate them on to one server running at 50%
utilization and "turn the other one off".
There are lots of virtualisation technologies VMware, Xen, Solaris 10 Zones,... Another thing to consider is that Solaris 10 zones have no overhead for CPU, IO, and network. Overheads reduced performance but they also require one to burn more CPU watts. But use whatever technology suits your needs.
...more on using fancy datacenter power saving technology tomorrow...
Friday Nov 17, 2006
The Total Tyranny of low utilization datacenters
In this blog and other blogs I've commented on, Woodcrest supporters always
want to say their servers are better at low utilisation. This is
totally the wrong way to go! They first claim typical datacenters are
running at low utilisations, example: Xen claims typical datacenters are at 15%.
Horrible, HORRIBLE.
So why shouldn't use just add all kinds of techniques to power at lower
utilisations, clearly that is the best way to save money? Right? Wrong.
Lets take a simple example of a 400 watt server(@ 100%) that saves 20 watts for
each 10% reduction in utilisation. Will show this in a table below and
compare equivalent work done compared to 100% so you can see the hyperbolic nature of the curve. Of course I'm only looking at one server so there
is some discretisation but when you have a datacenter it will quickly
approach these numbers.
| %Utilisation |
100% |
90% |
80% |
70% |
60% |
50% |
40% |
30% |
20% |
10% |
0% |
| Watts-at-Util |
400 |
380 |
360 |
340 |
320 |
300 |
280 |
260 |
240 |
220 |
220 |
| watts/work |
400 |
422 |
450 |
486 |
533 |
600 |
700 |
867 |
1200 |
2200 |
inf. |
Now that I've got you shocked, let's look at a more typical example.
Lets compare 5 servers running at 10% utilisation (that is 220 watts
each or 1100 watts for the 5 of them). A single server running at
50% utilisation only uses 300 watts! The 10% case
almost require 3.7 times more power! OUCH!
Bottom line: It is far too easy to be fooled to think you are saving
money if power-saving features at low utilisation is your answer.
By the by, a significant number of Sun's large servers run at over
80% utilisation using Solaris, of course.
Here is an example from 2004 of someone on different products who likely understands this math.
As reported in
Computerworld:
"Dennis Callahan, CIO at The Guardian Life Insurance Company of America in New York, server utilization has shot up to nearly 50% in the past 18 months, with a goal in coming years of nearly 70%.
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