User's Manual

254 Power Management
The CMC grants the requested power to the blade server, and the allocated
wattage is subtracted from the available budget. Once the server is granted a
power request, the server's iDRAC software continuously monitors the actual
power consumption. Depending on the actual power requirements,
the iDRAC power envelope may change over time. iDRAC requests a
power step-up only if the servers are fully consuming the allocated power.
However, under heavy load the performance of the server’s processors may be
degraded to ensure power consumption stays below or if the user-configured
System Input Power Cap if the Cap has been lowered from the factory
default setting.
The PowerEdge M1000e enclosure can supply enough power for peak
performance of most server configurations, but many available server
configurations do not consume the maximum power that the enclosure can
supply. To help data centers provision power for their enclosures, the M1000e
allows you to specify a System Input Power Cap to ensure that the overall
chassis AC power draw stays under a given threshold. The CMC first ensures
enough power is available to run the fans, IO Modules, iKVM (if present),
and the CMC itself. This power allocation is called the Input Power
Allocated to Chassis Infrastructure. Once the servers in an enclosure are
powered up, any attempt to set a lower System Input Power Cap that would
require a server to power off to fulfill this requirement will fail.
If necessary for the total power budget to stay below the value of the
System Input Power Cap, the CMC will allocate servers a value less than
their maximum requested power. Servers are allocated power based on their
Server Priority setting, with priority 1 servers getting maximum power,
priority 2 servers getting power after priority 1 servers, and so on.
Lower priority servers may get less power than priority 1 servers based on
System Input Max Power Capacity and user-configured setting of
System Input Power Cap.
Configuration changes, such as an additional server in the chassis, may
require the System Input Power Cap to be increased. Power needs in a
modular enclosure also increase when thermal conditions change and the fans
are required to run at higher speed, which causes them to consume additional
power. Insertion of I/O modules and iKVM also increases the power needs of
the modular enclosure. A fairly small amount of power is consumed by servers
even when they are powered down to keep the management controller
powered up. Additional servers can be powered up in modular enclosure only