ENERGY SAVINGS FROM
ENERGY STAR-QUALIFIED SERVERS
ENERGY STAR
7*
r Arc
f rep
ENE
ope
deli
II
A recent set of tests demonstrate that
replacing an older server with a new
ENERGY STAR-qualified model and modern
operating system will save energy
deliver more processing power in the bargain
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CONTENTS
ACKNOWLEDGEMENTS 1
OVERVIEW 2
ENERGY STAR SPECIFICATION 3
GOALS AND LIMITATIONS OF THE STUDY 3
TEST METHODOLOGY 3
TEST ENVIRONMENT 4
WORKLOADS 5
Baseline Workload 5
Web Fundamentals 5
FSCT 5
RESULTS 5
Baseline Workload 5
Web Fundamentals 8
FSCT 10
WHY NEWER HARDWARE AND OPERATING SYSTEMS ARE MORE ENERGY-EFFICIENT 12
Hardware 12
The Operating System 12
CONCLUSIONS 14
Expected Annual Savings 14
Savings Comparisons, Avoided Carbon Emissions 14
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ENERGY SAVINGS
from
ENERGY STAR-QUALIFIED
SERVERS
Prepared by
The Cadmus Group, Inc.
for
U.S. EPA ENERGY STAR®
August 2010
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ACKNOWLEDGEMENTS
A number of individuals made important contributions to this study. They include (in alphabetical order by
organization) Greg Davis and Scott Faasse from HP; Mark Aggar, Sean McGrane, Dan Reger, Bryan Weinstein, Bruce
Worthington, and Qi Zhang from Microsoft; Steve Ryan from the US EPA ENERGY STAR program, Mike Walker and
Eric Butterfield from Beacon Consultants Network Inc. (an ENERGY STAR technical support contractor), Robert
Huang from The Cadmus Group (an ENERGY STAR technical support contractor), and Tom Bolioli from Terra Novum
(an ENERGY STAR technical support contractor).
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OVERVIEW
Data centers use a lot of energy — nearly 3% of the electricity consumed in the United States, according to an
EPA report to Congress1. Because computer servers are at the core of data centers — and because the heat they
generate drives air conditioning costs —they are a prime target for energy-savings measures. Deploying more
energy-efficient servers is a very effective strategy for reducing energy consumption in the data center.
In tests conducted for this study, a newer ENERGY STAR-qualified server running a modern operating system
consistently used less power to deliver substantially better performance, compared to an older non-qualified
model running an older operating system.
?See http://www.energystar.g0v/i ndex.cfm?c=prod_development.server_efficiency_study
2
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ENERGY STAR SPECIFICATION
In May 2009, ENERGY STAR released its first energy
efficiency specification for computer servers. To earn
the ENERGY STAR, servers must offer the following
features:
+ Efficient power supplies that limit power conversion
losses and generate less waste heat, which
reduces the need for excess cooling where they are
housed;
+ Improved power quality, which provides building-
wide energy efficiency benefits;
+ Capabilities to measure real-time power use,
processor utilization, and air inlet temperature,
which improves manageability and lowers total cost
of ownership;
+ Advanced power management features and
efficient components to save energy across various
utilization levels, including idle;
+ A Power and Performance Data Sheetf or
purchasers that standardizes key information
on energy performance, features, and other
capabilities.
Microsoft graciously offered to host a metering study
at its Windows Server Performance Lab in Redmond,
Washington, and HP kindly donated server equipment for
the tests. Representatives from EPA, Microsoft, and HP
alike participated in the testing, from the initial operating
system installation process through the collection of test
results.
Before we describe that operating environment and
our test methodology, it is important to note that
a host of variables influence how much energy a
server consumes: server hardware, server software,
percentage of CPU utilization, input/output, and the
amount of storage access a given workload requires.
That said, it would have been too expensive and time-
consuming to conduct a study that looked at all of the
possible hardware, software, and workload variables.
As a result, the test team selected a typical three-
year-old server and a comparable new ENERGY
STAR-qualified server that might be considered as a
reasonable replacement. This scenario was intended
to mimic the type of decision faced by IT administrators
who are trying to save energy in their data center. The
team then set out to document energy consumption for
both servers over a wide range of workloads.
GOALS AND LIMITATIONS
OF THE STUDY
Today's servers deliver far more computing power
than models introduced just three to four years ago.
ENERGY STAR-qualified servers, however, provide that
additional computing performance using roughly 30%
less energy, according to EPA estimates. In late 2009,
EPA wanted to validate its original savings estimates
by measuring power consumed under various types of
workloads for two similar servers: one ENERGY STAR-
qualified, the other not. The goal was to realistically
measure how much electricity a new ENERGY STAR-
qualified model would save in a real-world operating
environment, compared to a typical three- to four-year-
old server.
TEST METHODOLOGY
The new ENERGY STAR-qualified server was the HP
ProLiant DL360 G6, using an out-of-the-box configuration
with a fresh operating system (OS) installation (Windows
Server 2008 R2). We compared this to an older HP
ProLiant DL360 G5 running Windows Server 2003 Service
Pack 2, which was not ENERGY STAR-qualified. The G5
was also set up with the out-of-the-box configuration
and a fresh OS installation.
Table 1 contains detailed specifications for the server
hardware provided by HP.
3
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TABLE 1: SERVER SPECIFICATIONS
SERVER
HP PROLIANT DL360 G5 ("OLD")
HP PROLIANT DL360 G6 ("NEW" ENERGY STAR-QUALIFIED)
OS
Windows Server 2003 SP2
Windows Server 2008 R2
Default Power
Management
HP Dynamic Power Saving Mode
HP Dynamic Power Saving Mode2 - OS Default Balanced
Power Policy
Hardware Available
to Public
June, 2006
March, 2009
Processor(s)
(2) Intel Xeon Dual-Core 5160
Processors (3.00 GHz)
(2) Intel Xeon Quad-Core X5560 Processors (2.80 GHz, HT
Enabled, Turbo Disabled by OS3)
Cache Memory
4MB Level 2 cache
8MB Level 3 cache
Memory
32 GB (8x4 GB) PC2-5300 Fully
Buffered DIMMs (DDR2-667)
32 GB (16x2 GB) PC3-10600R DIMMs (DDR3-1333)
Network Controller
Embedded Dual NC373i
Multifunction Gigabit NICs
(2) HP NC382i Dual Port Multifunction Gigabit NICs
Storage Controller
HP Smart Array P400 Controller
with 512MB BBWC, Smart Array
P800 controller
HP Smart Array P410i Controller with 512MB BBWC, Smart
Array P800 controller
Internal Drive
(2) 146GB SAS Disk drives
(2) 146GB SAS Disk drives
Optical Drive
IDE DVD-ROM/CDRW combo
Slim SATA DVD RW drive
Form Factor
Rack (1U)
Rack (1U)
Power Supply
(1) Hot Plug Fan and Power Supply
(Not Rated)
(1) 750W Hot Plug Power Supplies (80+ Gold certified)
Both servers were delivered by HP to the Microsoft Server Performance Lab and were racked "as-is"- no special
tuning was performed.
TEST ENVIRONMENT
The test environment was as follows:
+ Microsoft Windows Server Performance Lab
(climate-controlled server room, non-isolated hot/
cold aisles);
+ Standard rack (filled with active servers in hot/cold
isle configuration with no containment);
+ 1 Gigabit Ethernet and 10 Gigabit Ethernet (fibre
channel) network cards;
+ SAS arrays as external storage (for the Web
Fundamentals and FSCT workloads);
n
Processor Clocking Control (PCC). For additional information, see section entitled "Why Newer Hardware and Operating Systems
are More Energy-Efficient".
o
Turbo mode is disabled in Windows Server 2008 R2 balanced mode for the X5560 processor, but is enabled in balanced mode for newer Intel processors.
4 The manufacturer's data sheet claims that the accuracy of Watt readings (at23°C±5°C) is ± 0.2% of reading and ± 0.2% of range.
+ Instek GPM-8212R AC power meter (with RS232
communications cable)4;
+ Re-purposed servers acting as client machines (in
separate rack);
+ Controller running the workloads (that is, controlling
the clients) and interfacing with the power meter.
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WORKLOADS
We selected three workloads for our tests:
+ An industry-standard power and performance
workload (run as a baseline test)
+ Web Fundamentals
+ File Server Capacity Tool (FSCT)
BASELINE WORKLOAD
The baseline workload is an industry-standard,
CPU intensive benchmark used to compare power
and performance among different servers. It
measures power consumption for servers at different
performance levels —from 100 percent to idle in 10
percent segments — over a set period of time. The
graduated workload reflects the fact that processing
loads and power consumption vary substantially over
the course of days or weeks.
WEB FUNDAMENTALS
Web Fundamentals "Full Mix" is a web server
workload based on Microsoft.com usage patterns
and Microsoft IT proxy server traffic. Using the Web
Capacity Analysis Tool5 (WCAT 6.1) load generator, a
set of clients initiated by the controller generate HTTP
requests against the target web server. The workload
consists of requests for a combination of dynamic ASP.
NET pages and static files, some of which hit the file
cache. This test exercises the CPU, memory, disk, and
network, and is a good workload for performance and
scalability testing.
A limitation of this workload is that it consists mostly
of static file hosting and ASP Server Side Includes
(SSIs) in order to exercise the server side scripting
engine. There is no server side scripting beyond those
includes.
FSCT
The File Server Capacity Tool6 (FSCT) is a capacity
planning tool for Common Internet File System (CIFS),
Microsoft Server Message Block (SMB), and SMB2
file servers. The tool is also useful for identifying
performance bottlenecks for a file server workload.
FSCT results include the maximum number of users
for a file server configuration and throughput for that
configuration.
This benchmark performs a lot of hard disk access and
is very I/O intensive; it is generally unable to significantly
stress the CPU and memory before saturating the network
and/or disk I/O.
For this particular test, it was necessary to install
an additional 10 GB NIC and a higher performing
RAID controller in order to stress the G6 system. For
consistency's sake, these hardware items were added to
both the G5 and G6.
RESULTS
Under both workloads and the baseline benchmark,
the ENERGY STAR-qualified server, in combination with
Windows Server 2008 R2, provided significantly lower
energy consumption when performing the same number
of operations as the previous-generation hardware and
Windows Server release. Additionally, the ENERGY STAR-
qualified server consumed substantially less power overall
across all target loads in the Web Fundamentals and
baseline tests.
BASELINE WORKLOAD
Our results show significant across-the-board lower power
consumption at various loads on the ENERGY STAR-
qualified ProLiant G6 server with Windows Server 2008 R2.
On average, the G6with R2 consumed 26% less power than
the ProLiant G5 while handling the same target load. The
savings were larger for lower load levels.
The tables and graphs below detail the number of
transactions per second and the average power
consumption at each of the 10 target load levels tested.
On average, the ENERGY STAR-qualified G6 server with R2
delivered performance-to-power ratios 271% higher than
the non-qualified G5. Power-to-performance ratio is the
ratio of useful work (transactions per second) performed
per unit of power (watts) consumed by the system.
The G6 server with R2 delivered consistently lower power
usage over the older G5—as much as 36% less at the 10%
target load level and 54% less at idle. At the 50% target
load level, the G6 consumed 24% less power than the G5.
5 Ava il a bl e at http://www. i i s. nel/c omm u nity/d ef a u It. a s px?ta bi d=34&g =6&i=1467.
6 Ava il a bl e at http://www. mi c ro soft, c om/d ow nl oa d s/d eta i I s. a s px?d i s pi ayl a ng=e n&Fa mi ly ID=b20d b7f 1 -15f d - 40a e-9f3a -514968c65643.
5
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TABLE 2: DATA FROM BASELINE WORKLOAD
Load
Level
G5
Performance
G5 Avg.
Power
(Watts)
G5 Power
Efficiency
(Performance/
Watts)
G6
Performance
(Transactions/
Second)
G6Avg.
Power
(Watts)
G6 Power
Efficiency
(Performance/
Watts)
Difference
In Power
Consumed7
Difference
In Power
Efficiency8
100%
147,566
346
427
420,092
307
1369
11%
221%
90%
133,887
337
397
380,126
288
1321
15%
233%
80%
119,010
326
365
338,164
270
1255
17%
244%
70%
105,509
316
334
297,926
253
1177
20%
252%
60%
90,402
304
297
254,409
236
1078
22%
263%
50%
73,434
291
253
210,826
220
959
24%
279%
40%
60,175
281
214
169,079
206
822
27%
284%
30%
45,230
273
166
127,026
194
655
29%
295%
20%
30,248
267
113
85,272
183
466
31%
312%
10%
15,143
262
57.9
41,820
167
250
36%
332%
0%
(Active Idle)
0
256
0
0
119
0
54%
-
Averages:
26%
271%
FIGURE 1: BASELINE WORKLOAD - G5 POWER
AND POWER EFFICIENCY AT LOAD LEVEL
FIGURE 2: BASELINE WORKLOAD - G6 POWER AND
POWER EFFICIENCY AT LOAD LEVEL
Baseline Workload: G5
Baseline Workload: G6
/
Load Laval
I Power Efficiency (Performance/Watts)
•Average Power (Watts)
/
Load Laval
I Power Efficiency (Performance/Watts)
•Average Power (Watts)
^ Expressed as a percentage of G5 Average Power (Watts)
Expressed as a percentage of G5 Power Efficiency (Performance/Watts)
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FIGURE 3: BASELINE WORKLOAD - POWER
COMPARISON AT LOAD LEVEL
FIGURE 4: BASELINE WORKLOAD - THROUGHPUT
COMPARISON AT LOAD LEVEL
Baseline Workload: Power at Load Level
r 250
^ ^ ^ ^ ^ ^ ^ ^
Load Lavs!
Baseline Workload: Throughput at Load Level
450,000
_ 400,000
1 350,000
| 300,000
250,000
•| 200,000
I 150,000
I 100,000
- 50,000
0
vfc® ^ ^ ^ ^ ^ ^ ^
I Level
¦G5
»G6
•G5
•G6
FIGURE 5: BASELINE WORKLOAD - POWER
COMPARISON AT THROUGHPUT LEVEL
FIGURE 6: BASELINE WORKLOAD - POWER
EFFICIENCY COMPARISON AT LOAD LEVEL
Baseline Workload: Power at Throughput
100,000 200,000 300,000 400,000 500,000
Throughput
Baseline Workload: Power Efficiency at Load Level
1,600
_ 1,400
sl 1-200
11 1-000
£ I BOO
II 600
£ f 400
~ 200
0
f ^ ^ ^ ^ ^ ^ ^ <** <#«>*
I Laval
FIGURE 7: BASELINE WORKLOAD - POWER EFFICIENCY
COMPARISON AT THROUGHPUT LEVEL
Baseline Workload: Power Efficiency at Throughput
100,000 200,000 300,000 400,000 500,000
Throughput
(T ra msaction s/Se e and)
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WEB FUNDAMENTALS
Over the 10 target load levels tested, the ENERGY STAR-qualified ProLiant G6 with Windows Server 2008 R2 used an
average of 28% less power than the non-qualified ProLiant G5 server. In addition, the G6's performance-to-power
ratio was, on average, 330% higher than the non-qualified G5.
The G6 with R2 consistently consumed less power than the G5 across all target loads. At 10% target load, it
consumed 33% less power than the G5; at 50% target load, the G6 used 25% less power than the G5.
TABLE 3: DATA FROM WEB FUNDAMENTALS WORKLOAD
Load
Level
G5
Performance
(Responses/
Second)
G5 Avg.
Power
(Watts)
G5 Power
Efficiency
(Performance/
Watts)
G6
Performance
(Responses/
Second)
G6 Avg.
Power
(Watts)
G6 Power
Efficiency
(Performance/
Watts)
Difference
in Power
Consumed9
Difference
in Power
Efficiency1®
100%
21,959
324
68
69,978
264
265
18%
291%
90%
19,752
318
62
62,918
253
249
20%
300%
80%
17,552
312
56
55,910
236
237
24%
320%
70%
15,360
292
53
48,921
221
221
24%
320%
60%
13,163
277
48
41,922
211
199
24%
319%
50%
10,969
274
40
34,923
205
170
25%
326%
40%
8,777
271
32
27,936
197
142
27%
338%
30%
6,584
268
25
20,935
188
111
30%
352%
20%
4,390
264
17
13,962
182
77
31%
363%
10%
2,196
261
8
6,985
175
40
33%
375%
0%
0
256
0
0
119
0
54%
-
Averages:
28%
330%
FIGURE 8: WEB FUNDAMENTALS WORKLOAD - G5
POWER AND POWER EFFICIENCY AT LOAD LEVEL
FIGURE 9: WEB FUNDAMENTALS WORKLOAD - G6
POWER AND POWER EFFICIENCY AT LOAD LEVEL
Web Fundamentals: G5
Web Fundamentals: 66
Load Leval
Power Efficiency (Performance/Watts)
^^¦Average Power (Watts)
f
300
250
200
150
100
50
0
n
1
, 1
jl
r
I
4
¦ 1
i
ill
II
i
I
l
i
300
250 |
200 %
150
100
50
0
Load (LevaI
Power Efficiency (Performance/Watts)
verage Power (Watts)
Expressed as a percentage of G5 Average Power (Watts)
10
Expressed as a percentage of G5 Power Efficiency (Performance/Watts)
-------
FIGURE 10: WEB FUNDAMENTALS WORKLOAD -
POWER COMPARISON AT LOAD LEVEL
FIGURE 11: WEB FUNDAMENTALS WORKLOAD -
THROUGHPUT COMPARISON AT LOAD LEVEL
Web Fundamentals: Power at Load Level
Web Fundamentals: Throughput at Load Level
¦» 300
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Load Level
i 70,000
I 60,000
| 50,000
I 40,000
i 30,000
1 20,000
I 10,000
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Load Level
FIGURE 12: WEB FUNDAMENTALS WORKLOAD -
POWER COMPARISON AT THROUGHPUT LEVEL
Web Fundamentals: Power at Throughput
300
20,000 40,000 60,000
Throughput tRsqussts/S®cortid)
80,000
>Gb
-G6
FIGURE 13: WEB FUNDAMENTALS WORKLOAD -
POWER EFFICIENCY COMPARISON AT LOAD LEVEL
Web Fundamentals: Power Efficiency at Load Level
300
- 250
i
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
»G5 G6
FIGURE 14: WEB FUNDAMENTALS WORKLOAD - POWER
EFFICIENCY COMPARISON AT THROUGHPUT LEVEL
Web Fundamentals: Power Efficiency at Throughput
300
s 250
¦ p
| 200
| 150
| 100
CB
50
20,000 40,000 60,000
Throughput SRsqussWSasand!
80,000
•G5
»G6
-------
FSCT
In this workload, the ProLiant G5 was able to reliably serve 2800 users with a load of 256 operations per second
before the server reached its limits. The ENERGY STAR-qualified ProLiant G6with R2 was able to more than triple
this with 9443 users and 881 operations per second before reaching its limits. Despite this tripling of performance the
G6 with R2 was able to serve 881 operations per second using less energy than the idle power of the G5.
Note that the G6's CPU was barely stressed during this test. This was a function of the nature of the workload (as
mentioned previously), additional processor cores, and hyper threading.
TABLE 4: DATA FROM FSCT WORKLOAD - G5
Users
Overload11
Throughput
(Operations/
Second)
Average Power
CPU Utilization
(4 Logical
Processors)
Power Efficiency
(Throughput/
Watts)
560
0%
51
276
3.70%
0.18
1,120
0%
102
279.7
10.30%
0.36
1,680
0%
154
284.2
16.40%
0.54
2,240
0%
205
295.4
31.30%
0.69
2,800
1%
256
317.8
62.00%
0.81
All higher levels had excessive overload
TABLE 5: DATA FROM FSCT WORKLOAD - G6
Users
Overload
Throughput
(Operations/
Second)
Average Power
CPU Utilization
(16 Logical
Processors)
Power Efficiency
(Throughput/Watts)
560
0%
51
175
0.70%
0.29
1,547
0%
142
185
1.50%
0.77
2,534
0%
232
190.1
2.70%
1.22
3,521
0%
323
193.8
4.00%
1.67
4,508
0%
414
196.7
5.50%
2.1
5,495
0%
504
198.7
7.20%
2.54
6,482
0%
595
200.1
8.60%
2.97
7,469
0%
688
201.8
9.70%
3.41
8,456
0%
784
203.9
12.70%
3.85
9,443
1%
881
209.6
17.30%
4.2
All higher levels had excessive overload
Overload is a condition in which a system can't handle requests fast enough and starts dropping them. The number represents the percentage of
requests with no valid response.
-------
FIGURE 15: FSCT WORKLOAD - POWER
COMPARISON AT THROUGHPUT LEVEL
FIGURE 16: FSCT WORKLOAD - CPU UTILIZATION
COMPARISON AT THROUGHPUT LEVEL
FSCT: Power at Throughput
FSCT: CPU Utilization at Throughput
!
350
300
250
200
150
100
50
200 400 600
Throughput (Opsrattas/SeeiandS
800
1000
•G5
¦G6
200 400 600 800
Throughput (Opsrations/Sacond}
1000
•G5
¦G6
FIGURE 17: FSCT WORKLOAD - NUMBER OF
USERS COMPARISON AT THROUGHPUT LEVEL
FIGURE 18: FSCT WORKLOAD - POWER EFFICIENCY
COMPARISON AT THROUGHPUT LEVEL
FSCT: Power Efficiency at Throughput
0 200 400 600 800 1000
FSCT: Number of Users at Throughput
10000
8000
1000
»G5
¦G6
~G5
»G6
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WHY NEWER HARDWARE
AND OPERATING
SYSTEMS ARE MORE
ENERGY-EFFICIENT
HARDWARE
HP cites a number of reasons why its latest servers offer
improved power efficiency over previous generations:
common slot power supplies that are redundant, better
DC voltage regulators, Intel Xeon 5500 processors that
consume less power, and less power needed to operate
cooling fans.
HP ProLiant G6 servers make use of the company's
common slot power supply design that can be used
interchangeably across multiple platforms. According
to HP, these are more efficient at all power loads than
previous generations of HP power supplies. Common slot
power supplies allow planners to select a power supply
that will operate close to its maximum efficiency for the
planned server power load. For example, a 750-watt
power supply would be the optimal choice for a server
that has an average power load of 350 watts, since it
would be 92% efficient at that load, according to the
company. A 1200-watt power supply installed in that
same server configuration would only operate at 88%
efficiency.
Although in this test a single power supply was used,
redundant power supplies increase reliability. However,
in the past this could result in lower power efficiency. For
example, in G5 servers, both redundant power supplies
are online simultaneously; this lowers the amount of
power drawn from each supply, but has the potential to
decrease the power efficiency of each one. A feature of
the High Efficiency Mode (HEM) option on DL G6 servers
is that one of the redundant power supplies can be kept
in a standby state; this increases efficiency by allowing
the remaining supply to support the full power load. The
additional power supply is brought online only if the
primary supply fails.
The improved DC voltage regulators in the G6 servers
convert the 12-volt DC from the power supply into the
5-volt, 3-volt, and other feeds used by the various system
components. This results in an 8-point gain in DC power
efficiency over previous generations of servers,
according to the company.
Many ProLiant G6 servers use the Intel Xeon 5500
series processors, which have Intel's Intelligent Power
Technology. This is a set of features that can be used
to lower power consumption of the processor and
related subsystems when they are not fully utilized.
Most ProLiant servers also include the HP Power
Regulator Dynamic Power Savings mode feature,
which automatically optimizes processor power
consumption based on server activity. Power
Regulator is implemented in the system firmware and
directly monitors the instruction load of the server
processor(s) to determine the level of system activity.
Power Regulator uses this information to continuously
adjust the performance states, or p-states, of the
processor(s) to match processor power consumption
to the current workload without noticeably impacting
overall system performance.
The power management mode used in our G6 tests
combines the capabilities of HP Power Regulator with
the Balanced Power Policy in Windows Server 2008
R2. This is achieved using an interface that Microsoft
and HP jointly created called Processor Clocking
Control (PCC). The operating system calculates the
future performance requirements of each of the
processor cores on the system and communicates
these requirements to the DL 360 G6 using the PCC
interface. HP Power Regulator manages the power
controls on the processors and other components on
the system to deliver the requested performance level
for each core. PCC enables the hardware and software
to work together to delivery optimal power efficiency
for the workload running on the server.12
Additionally, ProLiant G6 servers can use up to 32
sensors to map the temperature profile inside the
server. Instead of using a fixed fan speed curve, a
proprietary feedback algorithm adjusts individual
fan speeds to maintain specific temperatures. This
prevents overcooling and lowers the overall power
consumption of the fans.
THE OPERATING SYSTEM
Windows Server 2008 R2 offers a number of power
control features as well as an optional "Enhanced
IP
Details of the PCC interface can be found at http://www.acpica.org/documentation/related_documents.php.
12
-------
Power Management" qualification program for
servers. For starters, it includes three in-box power
policies: Power Saver, Balanced (default) and
High Performance. The default Balanced policy
continuously alters the power states of the processors
in the system in response to the utilization level of the
workload. This ensures that processor power usage
maps to the needs of the workload, with minimal
impact to workload performance.
R2 achieves additional power savings by combining
processor power state control with a feature that
consolidates work onto a smaller number of processor
cores when workload utilization is low. This feature
is referred to as Core Parking. Processor cores that
aren't doing any work are placed into a deep sleep
state. This feature effectively scales the number
of processor cores in active use. Other features
such as Timer Coalescing and Intelligent Timer Tick
Distribution (or Tick Skipping), extend the time that
processor cores stay in deep sleep states by avoiding
waking cores unnecessarily.
The balanced power policy delivers power efficiency
out of the box. For workloads that prioritize lowest
latency and highest performance levels over power
efficiency, the High Performance power policy can be
used.
Although not featured in this study, these power
efficiency improvements apply to Hyper-V, offering a
significant reduction in platform interrupt activity and
enabling power savings and greater scalability for
virtual machines (VMs).
As described above, support for the new power
management interface called Processor Clocking
Control (PCC) was introduced in Windows Server
2008 R2. The operating system and platform use the
PCC interface to coordinate on power management.
Windows Server 2008 R2 uses the PCC interface to
pass future processor performance requirements to
the hardware, as a percentage of maximum frequency.
The hardware is in direct control of the processor
power states in this mode of operation and is
responsible for delivering the requested performance.
This enables both the OS and the platform to innovate
and add value in their respective domains which
results in improved power efficiency for the server.
This is the power management mode used for the
G6 testing detailed in this paper and is the default
configuration for new G6 servers with Windows Server
2008 R2.
Although not leveraged in this study, Windows Server
2008 R2 supports the new Power Meter and Budget
firmware (ACPI) interface that is included in the ACPI
4.0 specification. The interface can be used by Windows
Server to discover power monitoring and budgeting
hardware on the platform and to access power
consumption and power budget information.
Windows Server 2008 R2 exposes power information
to remote management software using WMI (Windows
Management Interface), which adheres to the DMTF
Power Supply Profile v1.01. This interface can be used
by developers to build software that can remotely
access power meter and budget information and modify
Windows Power Policy across groups of servers. System
Center Operations Manager 2007 R2 uses this interface
to provide centralized power management.
The Windows Server 2008 R2 server hardware logo
program includes an optional Additional Qualification
(AQ) called "Enhanced Power Management". This
qualification indicates that a server supports the
following features:
+ Power metering and budgeting hardware
+ Power Meter and Budget firmware (ACPI) interface
+ Enabling Windows power management
Hardware with this AQ will take full advantage of the
power management features in Windows Server 2008
R2, and will natively support the new SCOM 2007 R2
power management features. The HP DL360 G6 server
referenced in this paper is qualified for the Enhanced
Power Management AQ.
Although not leveraged in this study, remote power
metering capabilities are required for ENERGY STAR
compliance and provide datacenter administrators with
a valuable window into the power consumption and
cooling trends of servers in situ.
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CONCLUSIONS
Without doubt, server performance has increased over
the past 3 years. However, better performance does
not account for all -- or even the bulk of -- the energy
efficiency improvements we documented. Instead,
server hardware and software makers -- including
HP, Intel, and Microsoft -- have worked just as hard to
reduce platform power consumption, especially at lower
utilization levels. These tests suggest they have had
much success.
EXPECTED ANNUAL SAVINGS
Our findings imply that, at the average US commercial
rate for electricity of 10 cents per kilowatt hour (kWh),
the energy savings from a single ENERGY STAR-qualified
server could range from $60 (at 50% utilization) to $120 (at
idle) annually, or$240-$480 over the useful life of a server
(4 years).
In addition to using less energy themselves, ENERGY
STAR-qualified servers substantially reduce cooling
loads in data centers. A general rule of thumb suggests
that one watt saved by a server has the added benefit of
saving one to two watts of cooling power. This yields a
total savings of between $480 and $1,440 over the useful
lifetime of a server.
It's important to note that these power savings come
with a substantial increase in performance—at 50%
utilization, for example, the newer, more energy-efficient
server handles over three times the workload, thereby
reducing the number of systems needed to support the
same load.
SAVINGS COMPARISONS, AVOIDED CARBON
EMISSIONS
Because saving energy lowers demand on the nation's
power grid, it results in the generation of less electricity
and thus prevents pollution, too. Our data suggests that
a single ENERGY STAR-qualified server saves enough
electricity to avert nearly Y2 to 1 ton of carbon dioxide
emissions, based on the assumptions stated above.
Accounting for cooling savings makes it a total of 1 to 3
tons of carbon dioxide abated.
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v>EPA
United States
Environmental Protection
Agency
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