Users Guide

Power Supply Redundancy
When power supply redundancy is enabled, a PSU in the chassis is kept as a spare, ensuring that the failure of any one PSU
does not cause the servers or chassis to turn off. Power supply redundancy mode requires minimum two PSUs. Additional
PSUs, if present, are utilized to improve power efficiency of the system if DPSE is enabled. Subsequent failures after loss of
redundancy may cause the servers in the chassis to turn off.
Power Budgeting For Hardware Modules
CMC offers a power budgeting service that allows you to configure power budget, redundancy, and dynamic power for the
chassis.
The power management service enables optimization of power consumption and reallocation of power to different modules on
the basis of demand.
CMC maintains a power budget for the enclosure that reserves the necessary wattage for all installed servers and components.
CMC allocates power to the CMC infrastructure and the servers in the chassis. CMC infrastructure consists of components
in the chassis, such as fans, I/O module, and storage adapters, PCIe cards, physical disk, main board. The chassis may have
up to four servers that communicate to the chassis through an iDRAC. For more information, see the iDRAC User’s Guide at
dell.com/support/manuals.
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 turned on in an enclosure, the iDRAC software reestimates the power requirements and requests a subsequent
change in the power envelope.
CMC supplies the requested power to the server, and the allocated wattage is subtracted from the available budget. After the
server is granted a power request, the server's iDRAC software continuously monitors the actual power consumption. On the
basis of actual power requirements, the iDRAC power envelope may change over a period of time. iDRAC requests a power step
up if the servers are fully using the allocated power.
Under heavy load, the performance of the processors on the server may be degraded to ensure power consumption stays lower
than the user-configured System Input Power Cap.
The PowerEdge VRTX 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 datacenters allocate
power for their enclosures, the PowerEdge VRTX allows you to specify a System Input Power Cap to make sure that the overall
chassis AC power draw stays within a given threshold point. CMC first makes sure that enough power is available to run the
fans, I/O module, storage adapters, physical disk drive, main board, and CMC itself. This power allocation is called the Input
Power Allocated to Chassis Infrastructure. After Chassis infrastructure, the servers in an enclosure are turned on. Any attempt
to set a System Input Power Cap less than the “Power Burden” will not be successful. Power Burden is the sum of power
allocated to the infrastructure and the minimum power allocated for the powered servers.
NOTE: To use the Power Cap feature, you must have an Enterprise License.
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-one 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, shared HDDs, or PCIe cards 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 module and storage adapters,
PCIe cards, physical disk, main board; number, type, and configuration of PSUs also increase 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 the modular enclosure only if sufficient power is available. The System Input Power Cap
can be increased any time up to a maximum value of 5000 Watt to allow the power up of additional servers.
Changes in the modular enclosure that reduce the power allocation are:
● Server turned off
164
Managing and Monitoring Power