Figure 22. Pmbus Communication Channels - Dell PowerEdge M1000e Technical Manual

The system administrator can also set priorities for each server module. The priority works in
conjunction with the CMC power budgeting and iDRAC power monitoring to ensure that the lowest
priority blades are the first to enter any power optimization mode, should conditions warrant the
activation of this feature.
Power capping is set at the chassis level for our blade servers and not at the blade-server level, so
components like a processer or memory can throttle down when necessary on lower priority blade
servers. An allocation is taken out for a component (fans, I/O modules), the remainder is applied to
the blades, and then throttling is applied if required to get under the cap. If all the blades are set up
with the same priority, they start throttling down the processor, memory, and so on. A variety of
BIOS settings throttle the processor or not, depending on load.
If power consumption demands exceed available power, the enclosure throttles back the power
supplied to blades as prioritized in the CMC. The blades do not shut down; rather they slow down if
necessary; Dell designed the system this way on purpose, in response to customer feedback that
they did not want the blades to shut themselves down under any condition. I/O modules, on the
other hand, are shut down prior to permanent damage, as they are less tolerant to power variation
than the blade server hardware.
The M1000e is compliant with the PMBus Specification 1.1 using this power management standard
for status, measurement, and control. The M1000e power supplies continuously monitor AC input
current, voltage and power, enabling exposure of data to enterprise-level management tools, such
as Dell's OpenManage Power Center. Real-time power consumption is viewable per system.
For more information on Dell OpenManage Power Center, visit
Each power supply communicates information about itself through the PMBus (I2C bus):

Vendor part number

Revision serial number

Power capability
Each power supply performs the following functions:

Control for the main power regulator

Reports power-supply status across the PMBus
Input/Output Voltage/Current
—
AC power consumption
—
PowerEdge M1000e Technical Guide
47

Figure 22. PMBus communication channels

Dell OpenManage Power Center.