User's Manual

294 Power Management
iDRAC provides CMC with its power envelope requirements before powering
up the server. The power envelope consists of the maximum and minimum
power requirements necessary to keep the server operating. iDRAC’s initial
estimate is based on its initial understanding of components in the server.
After operation commences and further components are discovered, iDRAC
may increase or decrease its initial power requirements.
When a server is powered-up in an enclosure, the iDRAC software re-estimates
the power requirements and requests a subsequent change in the power
envelope.
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 AC 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.