User's Manual

Carrier Grade Chassis Management Controller User’s Guide Addendum 11
CMC grants the requested power to the 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.
Under heavy load the performance of the server's processors may be degraded
to ensure power consumption stays below the user-configured System Input
Power Cap. 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 input power draw stays under a given threshold. CMC first ensures
enough power is available to run the fans, IO Modules, iKVM (if present),
and CMC itself. This power allocation is called the Input Power Allocated to
Chassis Infrastructure. Following Chassis Infrastructure, the servers in an
enclosure are powered up. Any attempt to set a System Input Power Cap
below the actual consumption fails.
If necessary for the total power budget to stay below the value of the System
Input Power Cap, CMC allocates servers a value less than their maximum
requested power. Servers are allocated power based on their Server Priority
setting, with higher priority 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 the 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.