HP BladeSystem p-Class rack-centralized (3U) power solutions

enclosure and continues until the bottom right server blade in the bottom server blade enclosure is

powered up.

In a rack that contains many server blade enclosures, the sequencing process may cause a significant

time delay which could exceed 5 or 10 minutes before the last server blade powers up. However, this

is preferable to the alternative―the possibility that the main breakers trip due to the excessive load on

the AC infrastructure as all the server blade enclosures try to power up simultaneously.

The “Properly configure power zones” section under “Recommendations” in this paper describes

power zones in more detail.

How server blades power up

For a p-Class server blade to power on, the necessary power must be available from the rack-

centralized power subsystem. The iLO management processor on each server blade verifies with the

power management module that there is sufficient power before automatically powering on the server

blade.

Once iLO receives a power-on request, it reads the EEPROM on the server blade to determine the

maximum blade wattage that could be required by a fully configured server blade. The iLO

management device sends a request for that wattage amount to the enclosure management module in

the server blade enclosure, which then forwards the request to the power management module in the

power enclosure. If—without exceeding the maximum power load—sufficient power is available to

operate the additional server blade at its peak load and to meet redundancy requirements, then the

power subsystem signals that the server blade may power up. If there is not enough power available,

the iLO management device continues to retry the power-on request at 15-second intervals. After one

minute, iLO continues retrying the power-on request in 5-minute intervals to reduce traffic on the

communication bus.

After a server blade powers up, the ROM and iLO collect data about the actual server blade

hardware configuration. The data allows the power management module to adjust the power

allocation for that server blade to the actual maximum wattage required.

This increases the

remaining power available for other server blades to be installed.

NOTE: Power for disk drives is always reserved and is never

returned, even if no drives are installed, as a drive could always

be hot-plugged into the system while it is operating.

Because the initial request is made for maximum power rather than based on the actual configuration,

the server blade may not automatically power up even though there is sufficient power available.

Manual power on

Occasionally, an administrator may want to power on a server blade even when the power

management module indicates there is insufficient power—for example, when a non-redundant power

configuration is adequate. The iLO management device allows administrators to perform a power

override on the server blade in either of two ways: by pressing the server blade power button down

for at least 5 seconds or by selecting the manual override button from the iLO virtual power button.

The manual override must be used very carefully to avoid possible loss of service and data.

This functionality is not available for the HP ProLiant BL40p or the first generation HP ProLiant BL20p.