Ultra-Dense Server Deployment in Racks

Compaq Ultra-Dense Server Deployment in Compaq Racks 15
128H-0400A-WWEN
As stated earlier, the power supply is designed to support future processor and hard drive upgrades. When
installing 42 servers, the number of PDUs to be installed will depend on the support for the input current
requirement. Carefully de-rating the input power may very well satisfy deployment needs and also reduce
the number of PDUs per rack. Reducing the number of PDUs has a direct impact on the deployment time
and maintenance of an installation.
The remainder of this section explains the input power relationships to input current and thermal
dissipation to aid customers in de-rating the input power.
2.2.1. Input Current and Thermal Dissipation Calculations
The input power is the key in deriving the input current and thermal dissipation. For a given input power,
the input current will vary depending on the input voltage level.
The relationship among the current, the voltage and the power for the power supply input is as follows:
For example,
Input Current = 100W /110V = 0.91A
Input Current = 100W /208V = 0.48A
The input power of a server depends on the operational state of the system. For example, during the initial
power up, a server consumes more power due to the hard disk drives spin-ups. It should be noted that in
ProLiant DL360, the two hard disk drives spin-up one after the other. Therefore, the peak input power
requirement changes significantly when the first drive is added, but not as much when the second drive is
added. After the power up, the input power varies depending on the operating system and the application
software running on the server. During standby, only the auxiliary portion of the power supply is
consuming power to support operations of a very limited part of the system, for example, the Remote
Insight Lights-Out Edition option, NICs, and so on.
The thermal dissipation can be calculated from the input power as follows:
For example,
Thermal Dissipation = 100W * 3.41 = 341 BTUs/hour
Thermal Dissipation = 292W * 3.41 = 996 BTUs/hour
The easiest way to calculate the thermal dissipation for the entire rack is to add the input power
requirements for all the servers and other units populated in a rack, and then multiply the total input power
by 3.41.
Section 2.2.3 explains more on how adding or removing of an optional subsystem component affects the
input power and thermal calculations.
Input Current = Input Power / Input Voltage
Thermal Dissipation = Input Power * 3.41