User's Manual

292 Power Management
The iDRAC provides the 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.
The 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. 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. Following Chassis Infrastructure, the
servers in an enclosure are powered up. Any attempt to set a System Input
Power Cap below the actual consumption 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 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.