HP ProLiant DL140 - G2 Server Reference manual

Critical factors in intra-rack power distribution planning
for high-density systems
technology brief, 2nd edition
Abstract.............................................................................................................................................. 2
Introduction......................................................................................................................................... 2
Key factors of power distribution in high-density racks.............................................................................. 3
Power level and phase...................................................................................................................... 3
Connector types............................................................................................................................... 4
Power consumption .......................................................................................................................... 5
Space issues.................................................................................................................................... 6
Segmented power distribution ........................................................................................................... 7
Redundant power distribution ............................................................................................................ 8
Power circuit monitoring ................................................................................................................... 9
Other considerations ........................................................................................................................ 9
Sample power distribution solutions ..................................................................................................... 10
Rack configurations for distributing power to HP ProLiant c-Class servers .............................................. 10
Rack configurations for distributing power to HP ProLiant DL servers..................................................... 12
Conclusion........................................................................................................................................ 13
For more information.......................................................................................................................... 13
Call to action .................................................................................................................................... 13

Abstract
As server densities per rack increase, the power densities for those racks increase as well. This paper
identifies critical factors that infrastructure designers and system administrators must consider to plan
safe and efficient power distribution systems for high-density racks.
Introduction
Power distribution in the data center is changing with the continued increase in server density per
rack. The processing power housed in a row of racks a few years ago has been compressed into the
space of one rack or less. While the space needed for a given amount of processing has been
reduced, the power requirements have been consolidated—and they are growing.
Early methods of distributing power within a rack (intra-rack power) are simply inadequate for
meeting the increasing power requirements for racks of high-density equipment. Intra-rack power
distribution technology is evolving to provide the levels of power required by racks of high-density
servers.
Accurately determining the power distribution needs for a rack of high-density servers requires
considering the following factors:
•Voltage level provided by the facility
•Type of power connectors to be used
•Estimated power consumption
•Power redundancy
•System expansion
•Serviceability
Failure to account for these factors can result in unscheduled downtime from equipment damage or
overloads, increased costs, and safety issues. This paper explains the significance of these and other
factors in planning for high-density computing.
2

Key factors of power distribution in high-density racks
Power distribution units (PDUs) are highly recommended for high-density systems that place heavy
loading demands on the facility alternating current (AC) power bus. PDUs allow IT infrastructure
designers to:
•Use segmented circuits to improve serviceability and enable sequential startup
•Achieve balanced loading between dual power buses
•Support redundant operation of equipment with redundant power supplies
A variety of PDU types are available to meet different needs. Key considerations for choosing an
appropriate PDU include:
•Level and phase of power to be distributed
•Connector type
•Estimated power consumption of active components in the rack
•Physical space available for PDU mounting
•Special requirements or features such as circuit monitoring
Power level and phase
PDUs are designed to distribute a specific amount of current at either a low-line (100 – 127 VAC) or
high-line (200 – 240 VAC) voltage range, depending on which level is supplied to the rack. Most HP
server equipment features auto-sensing input circuitry that automatically detects and adjusts to the
input voltage range.
High-line voltage is the favored choice for electrical equipment requiring high power consumption. As
determined by Ohm’s law [voltage (E) x current (I) = power (W)], higher voltage allows power
supplies to produce the necessary power with less AC current. For example, a power supply that is
required to produce 400 watts of power for a server will need to draw 3.3 amperes if operated with
120 VAC. The same power supply operating at 208VAC only requires 1.9 amperes to produce
400 watts—over a 30 percent reduction of AC current. High-line operation is generally more
economical because it allows power supplies to create less heat (thereby reducing the cooling
requirements). High-line voltage also can enhance reliability by extending equipment meantime-
between-failure (MBF) periods. Note that some power supplies require high-line voltage to operate at
maximum potential.
High-line voltage (208 VAC in North America, 200 VAC in Japan, 220 VAC elsewhere) is becoming
commonly available in data centers. High-line voltage can be distributed as single or three-phase
power. With single-phase power, voltage reaches its maximum and minimum 120 times a second (at
60 Hz). Three-phase power uses three cycles 120 degrees out of phase to provide a more constant
voltage to the load (Figure 1). The efficiency of three-phase power allows the use of smaller circuit
sizes (smaller-gauge conductors) to distribute the same amount of AC power.
Figure 1. Comparison of single- and three-Phase AC
Single-Phase AC
Three-Phase AC
3

Connector types
Local and national electrical codes specify the types of connectors that should be used when
interfacing with facility AC feeds. The location of the facility and the level, amount, and phase of the
AC power available determine the type of connector to use. PDUs are designed to distribute power at
a specific range and current. PDUs are provided with power cords of appropriate sizes and plug
types for the geographic region where they will be used. Table 1 shows profiles of the most common
connectors for different regions. Some regions may require connectors not shown in Table 1. Some
facilities may require PDU power cords without connectors for hard-wired (terminal) installations.
Table 1.AC power connectors (rack-to-facility interface)
Geographic region
or country Low-line High-line
North America & Japan NEMA 5-15
NEMA 5-20
NEMA L5-30
NEMA 6-15
NEMA L6-20
IEC 309 2 phase [1]
IEC 309 3 phase [1]
Europe n/a
Shuko
United Kingdom n/a BS1363
[1] Becoming more common in other regions.
For more information on AC power connector types refer to the HP technology brief “Selecting power
cords and jumper cables for use with HP ProLiant servers” at the following URL:
http://h18004.www1.hp.com/products/servers/technology/whitepapers/datacenter.html
4

Power consumption
The type (low-line or high-line) and amount of power (in VA) required by the equipment in a rack
largely determines the type of PDU(s) to use. HP provides online power calculators for making
accurate power consumption estimates for most ProLiant servers. Each calculator (Figure 2) allows the
IT infrastructure designer to predetermine the power requirements for a server chassis according to
configuration parameters entered into the calculator. With accurate estimates of power requirements
for individual server chassis, infrastructure designers can easily calculate power consumption for a
fully-configured rack.
A catalog of HP Power Calculators is available for downloading at the following URL:
http://h71028.www7.hp.com/enterprise/cache/80364-0-0-0-121.aspx?jumpid=reg_R1002_USEN
Figure 2. HP Online Power Calculator (partial screen)
The HP Online Power Calculator also provides estimates of current draw, watts consumed, and inrush
current. These are factors to consider when choosing PDUs. The HP Online Power Calculator also
provides a BTUs/hr calculation for planning the cooling requirements of an installation.
5

Space issues
The 1U and blade server form factors allow for high-density installations that can occupy 100 percent
of the front U space in a rack. This leaves only rear U or side (“zero U”) space for mounting power
distribution components. HP has designed components to address space issues that are becoming
more acute in today’s high-density systems. HP modular power distribution components include a
control core module that offers flexible mounting options as illustrated in Figure 3.
Figure 3. Modular PDU mounting methods
Control Core
Control Core Extension Strip
Extension Strip
1U (Horizontal)
Front or Rear Rack Mountin
g
0U (Vertical)
Side Rack Mountin
g
HP Monitored PDUs are self-contained in an extension strip form factor and designed to mount
vertically in the same manner as the extension strips shown in Figure 3.
Note that some server systems may occupy most of a standard-sized rack space. They leave little
room for power components or cables. These systems may require a rack extension kit (Figure 4) to
accommodate cables and PDUs and to allow access to field-serviceable components. Two optional
rack extensions kits, a 42U kit and a 36U kit, are available for the HP 10000 series equipment racks.
Figure 4. Rack extension kit
Rack Extension Kit
To
p
View
Side View
6

Segmented power distribution
In high-density systems where a single rack can support hundreds of users at a time, the power
infrastructure should be designed so that a single system failure will have minimal effect on overall
operations. Segmenting servers into groups for power distribution reduces the chance for unscheduled
downtime resulting from overload or maintenance conditions that might otherwise shut down
everything else in the rack. Segmenting servers into two or more groups also facilitates proper cable
management and serviceability.
Segmenting can reduce the amount of inrush current associated with servers by allowing IT
administrators to sequentially power up server groups. Circuits can be segmented by using a modular
system of control cores and extension strips (Figure 5A) or by using monitored PDUs that individually
support multiple load segments (Figure 5B). In either case, a circuit breaker is associated with each
load segment (LS).
Figure 5. Segmented power distribution
VAC in
p
ut
LS2
Ext.
Strip
LS1
Ext.
Strip
A
. Segmenting with
HP Modular PDU com
p
onents
PDU
PS A
PS B
HP ProLiant
servers
1 thru 8
PS A
PS B
HP ProLiant
servers
9 thru 16
To other
extension strips
Control Core
PS A PS B
HP ProLiant
servers
9 thru 16
PS A PS B
HP ProLiant
servers
17 thru 24
VAC in
p
ut
B. Segmenting with an
HP Monitored PDU com
p
onent
PS A PS B
HP ProLiant
servers
1 thru 8
LS1
LS2
LS3
7

Redundant power distribution
Redundant power systems require two power distribution circuits, one for each power bus. Redundant
operation requires configuring servers with redundant power supplies, each capable of supporting the
full load of a server, if necessary. For redundant operation, the PDU or PDUs for each bus should be
configured to handle less than half of their rated capacity for normal operation so that they can
handle the full load of the system if one bus fails. The example shown in Figure 6 is based on an HP
ProLiant server with a current draw of 1.9A operating with 208 VAC common to North America and
Japan. The PDU for each bus feed must handle the full rack load (in this case, 32A) if one bus fails. In
Figure 6, multi-segment 40A PDUs satisfy this requirement with adequate headroom.
Figure 6. Redundant power distribution
Normal o
p
eration
(
see note below
)
40A
PDU
16 A
Bus A
208 VAC
(
see text below
)
40A
PDU
16 A
32A
Redundant operation
(
Bus A failure
)
PS A
PS B
HP ProLiant
servers
1 thru 8
PS A
PS B
HP ProLiant
servers
9 thru 16
Bus B
208 VAC
(
see text below
)
However, if the system in Figure 6 were operating in a 230 VAC environment, 32A PDUs could be
used. The current draw of the same ProLiant server operating 230 VAC will be 1.7A each, resulting
in a PDU current load of 13.6 A for normal operation and 27.3 A for all16 servers in redundant
operation.
NOTE:
Depending on the server system employed, the actual load
on redundant buses during normal operation may not be
evenly divided.
8

Power circuit monitoring
Enterprise data systems can be maintained efficiently with minimum manpower by employing
components that continuously monitor current loading on power circuits. Monitored systems make it
easier to balance power distribution circuits, to gauge expansion capabilities, and to avoid
unscheduled downtime resulting from circuit overloading or equipment damage.
Monitored PDUs from HP include an integrated display panel that provides:
•Real-time measurement of current load on each load segment
•Out-of-range voltage indication (10 to 20 percent under-voltage or over-voltage condition)
•Load warning alarms for each load segment (load detection of 80 to 102 percent rated capacity)
•Overload warning for each load segment (load detection of 102 percent or greater than rated
capacity)
For maximum convenience, HP monitored PDUs can accept an optional PDU Management Module.
This module enables IT administrators to monitor one or a pair of HP Monitored PDUs over a network.
The HP PDU Management Module can be accessed through the built-in web interface or the text-
based serial/Telnet interface. The HP PDU Management Module can also be integrated with SNMP
management software such as HP Systems Insight Manger (SIM) that can receive and log SNMP traps
(alerts) to manage alarm conditions.
Other considerations
An effective power distribution solution for a high-density rack involves much more than meeting the
power requirement needs of rack-mounted components. Factors including cable routing, air flow, and
cooling can also become critical in high-density systems. For more information on these and other
related subjects, refer to the HP technology papers web site at the following URL:
http://h18004.www1.hp.com/products/servers/technology/whitepapers/index.html
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Sample power distribution solutions
This section includes examples for implementing power distribution methods for various rack
configurations. These configurations are examples only. Numerous configurations may be appropriate
depending on factors mentioned earlier such as:
•Server power consumption
•Server configuration (number of processors, hard drives, expansion cards, etc.)
•Server utilization
•Redundant/non-redundant requirements
NOTE:
These sample configurations do not take into account
battery backup (UPS) considerations.
Rack configurations for distributing power to HP BladeSystem c-Class
servers
This section describes power distribution configurations based on the HP BladeSystem c-Class system
using the HP BladeSystem c7000 Enclosure and modular or monitored PDUs (Figure 7). The HP
BladeSystem c7000 Enclosure uses auto-ranging power supplies and supports redundant power
supply configurations. Up to four BladeSystem c7000 enclosures can be installed in a standard 42U
rack.
Figure 7. HP ProLiant c-Class system and power distribution components
Modular PDU
Monitored PDU
HP c7000 Enclosure
with server blades
Table 2 shows the suggested PDU configurations when using one to four HP BladeSystem c7000
enclosures in a standard rack.
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Table 2. Power distribution configurations for using one to four HP BladeSystem c7000 enclosures in
a standard rack
No. of
c7000
enclosures
Input
Feed
Recommended HP
PDU with AC input plug type
No. of
PDUs
Reqd. [1]
1Ф
output
current
per PDU
Total 1Ф
output
current
available
[3]
Total output
power
available
1Ф
208VAC
Modular, 252663-D75
w/CS8265 50A non-NEMA
2 40 80 A 16.6 kW
1
1Ф
220VAC
Modular, 252663-B34
IEC309 60A 3-wire blue
2 40 80 A 17.6 kW
1Ф
208VAC
Modular, 252663-D75
w/CS8265 50A non-NEMA
4 40 160 A 33.3 kW
1Ф
220VAC
Modular, 252663-B34
IEC309 60A 3-wire blue
4 40 160 A 35.2 kW
3Ф∆
208VAC
Monitored, AF916A
w/IEC309 60A 4-wire blue
2 84 168 A 35.0 kW
2
3ФY
220VAC
Monitored, AF917A
w/IEC309 32A 5-wire red
2 96 192 A 42.2 kW
1Ф
208VAC
Modular, 252663-D75
w/CS8265 50A non-NEMA
6 40 240 A 50.0 kW
1Ф
220VAC
Modular, 252663-B34
w/IEC309 60A 3-wire blue
6 40 240 A 52.8 kW
3Ф∆
208VAC
Monitored, AF916A [2]
w/IEC309 60A 4-wire blue
2 84 168 A 35.0 kW
3ФY
220VAC
Monitored, AF917A [2]
w/IEC309 32A 5-wire red
2 96 192 A 42.2 kW
3
3ФY
220VAC
Monitored, AF917A [2]
w/IEC309 32A 5-wire red
4 96 384 A 84.5 kW
1Ф
208VAC
Modular, 252663-D75
w/CS8265 50A non-NEMA
8 40 320 A 67.0 kW
1Ф
220VAC
Modular, 252663-B34
w/IEC309 60A 3-wire blue
8 40 320 A 70.4 kW
3Ф∆
208VAC
Monitored, AF916A [2]
w/IEC309 60A 4-wire blue
2 84 168 A 35.0 kW
4
3ФY
220VAC
Monitored, AF917A [2]
w/IEC309 32A 5-wire red
4 96 384 A 84.5 kW
[1] The number of required PDUs coincides with number of facility AC feeds. For PDU choices, access the online
PDU matrix through the URL provided in the “For more information” section.
[2] Configuration requires optional 600mm rack extension kit (P/N AF058A).
[3] Redundant operation requires double this amount of Total 1Фoutput current.
Products and part numbers discussed in this document are subject to change without notice. For the
latest product and part numbers, access the URL provided in the “For more information” section.
11

Rack configurations for distributing power to HP ProLiant DL servers
This section describes power distribution configurations for a high-density server system based on HP
ProLiant DL 360 G5 servers. The ProLiant DL 360 G5 is a 1U server that uses an auto-ranging power
supply and supports power redundancy when used in the 1 + 1 power supply configuration option.
These configurations use monitored PDUs and fixed cord extension bars (Figure 8).
Figure 8. HP ProLiant DL360 G5 system and power distribution components
HP ProLiant DL360 G5 server
Monitored PDU
Fixed cord
Extension Bar
Table 3 shows the difference in power requirements of the ProLiant DL360 G5 server when it is used
in two different scenarios. In one scenario, the server is configured and utilized to about half its
potential. In the other scenario, the server is nearly at maximum configuration and estimated to run at
a relatively high (70 percent) state of use. Both configurations employ redundant power (two supplies
per system) and use high-line voltage. The maximum configuration operates off three-phase power.
Although a standard 42U rack can physically accommodate 42 ProLiant DL360 G5 servers, it is
advisable to leave space for server expansion, power distribution components such as PDUs and
UPSs, keyboard/video/mouse (KVM) equipment, and/or networking components.
Table 3. HP ProLiant DL360 G5 server power distribution configurations
No. of
servers
in rack
System configuration
(each server)
Total VA
required
Total
current
draw
No./type
of outlets
required Recommended PDU
30 One 2.0-GHz processor,
2 GB memory, one PCI-E
card, two 36 GB hard
drives, system utilization
estimated at 40%
8.5 kVA 36 A 60/C13 1Ф208VAC:
Monitored PDU AF506A (x2)
or monitored PDU AF505A
1Ф220VAC:
Monitored PDU AF508A (x2)
30 Two 3.0-GHz
processors, 16 GB
memory, two PCI-E
cards, four 146-GB SAS
hard drives, system
utilization estimated at
70%
14.5 kVA 60 A 60/C13 3Ф208VAC:
Monitored PDU AF916A
and
fixed cord extension bar
351655-B21 (x5)
3Ф220VAC:
Monitored PDU AF509A (x2)
Products and part numbers discussed in this document are subject to change without notice. Refer to
the URL provided in the “For more information” section for the latest available products and part
numbers
Total VA and current requirements were determined using the HP Power Calculator Utility available at
the following URL:
http://h30099.www3.hp.com/configurator/calc/Power%20Calculator%20Catalog.xls
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Conclusion
High-density server systems that draw significant amounts of facility power require careful
consideration to ensure that safety, availability, and manageability are not compromised. The variety
of power distribution products available from HP allows an almost unlimited number of power
distribution configurations to satisfy those goals.
NOTE:
Products and part numbers discussed in this document are
subject to change without notice. Refer to the URL provided
in the “For more information” section for the latest available
products and part numbers.
For more information
For additional information, refer to the resources listed below.
Resource Hyperlink
HP power distribution products http://h18004.www1.hp.com/products/servers/prol
iantstorage/power-protection/pdu.html
HP PDU comparison chart http://h18004.www1.hp.com/products/servers/prol
iantstorage/power-protection/power-
distribution/powermonitoring/index.html
HP Industry Standard Servers
technology papers http://h18004.www1.hp.com/products/servers/tec
hnology/whitepapers/index.html.
HP remote management technology http://h18013.www1.hp.com/products/servers/managem
ent/remotemgmt.html?jumpid=hpr_R1002_USEN
Call to action
Send comments about this paper to [email protected].
© 2007 Hewlett-Packard Development Company, L.P. The information contained herein is
subject to change without notice. The only warranties for HP products and services are set forth
in the express warranty statements accompanying such products and services. Nothing herein
should be construed as constituting an additional warranty. HP shall not be liable for technical
or editorial errors or omissions contained herein.
TC070503TB, May 2007
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