78 IBM PureFlex System and IBM Flex System Products and Technology
Installing six 80 mm fan modules installed allows a further four nodes to be supported within
the chassis. The maximum therefore is eight as shown in Figure 4-22.
Figure 4-22 Six 80 mm fan modules allow for a maximum of eight nodes
To cool more than eight nodes, all fan modules must be installed as shown in Figure 4-23
Figure 4-23 Eight 80 mm fan modules support for 9 to 14 nodes
If there are insufficient fan modules for the number of nodes installed, the nodes might be
throttled.
4.7.2 Power supply population
The power supplies can be installed in either N+N or N+1 configuration. N+N means a fully
redundant configuration where there are duplicate power supplies for each supply needed for
full operation. N+1 means there is only one redundant power supply and all other supplies are
needed for full operation. To support a full chassis of Nodes, N (the number of power
supplies) must equal 3 for N+N operation. N must be greater than or equal to 3 for N+1
operation.
As the number of nodes in a chassis is expanded, more power supplies can be added as
required. This system allows cost effective scaling of power configurations.
Rear View
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If there is not enough DC power available to meet the load demand, the Chassis
Management Module automatically powers down devices to reduce the load demand.
Power policies
There are five power management policies that can be selected to dictate how the chassis is
protected in the case of potential power module or supply failures. These policies are
configured by using the Chassis Management Module graphical interface.
AC Power source redundancy
Power is allocated under the assumption that no throttling of the nodes is allowed if a
power supply fault occurs. This is an N+N configuration.
AC Power source redundancy with compute node throttling allowed
Power is allocated under the assumption that throttling of the nodes are allowed if a power
supply fault occurs. This is an N+N configuration.
Power Module Redundancy
Maximum input power is limited to one less than the number of power modules when more
than one power module is present. One power module can fail without affecting compute
note operation. Multiple power node failures can cause the chassis to power off. Some
compute nodes might not be able to power on if doing so would exceed the power policy
limit.
Power Module Redundancy with compute node throttling allowed
This can be described as oversubscription mode. Operation in this mode assumes that a
nodes load can be reduced, or throttled, to the continuous load rating within a specified
time. This process occurs following a loss of one or more power supplies. The Power
Supplies can exceed their continuous rating of 2500w for short periods. This is for an N+1
configuration.
Basic Power Management
This allows the total output power of all power supplies to be used. When operating in this
mode, there is no power redundancy. If a power supply fails, or an AC feed to one or more
supplies is lost, the entire chassis might shut down. There is no power throttling.
The chassis run in one of these power capping policies:
No Power Capping
Maximum input power is determined by the active power redundancy policy
Static Capping
This sets an overall chassis limit on the maximum input power. In a situation where
powering on a component would cause the limit to be exceeded, the component is
prevented from powering on.
80 IBM PureFlex System and IBM Flex System Products and Technology
Power supplies required in an N+N configuration
A total of six PSU can be installed and, in an N+N configuration, the options are either 2, 4, or
6 power supplies installed.
The chassis ships with Power supply bay 1 and 4 preinstalled. For N+N, this configuration
allows up to four nodes to be populated into the chassis before requiring any additional power
supplies. Figure 4-24 shows this configuration.
Figure 4-24 N+N with four nodes installed
For up to eight nodes with N+N configuration, install a further pair of power supplies in bays 2
and 5 as shown in Figure 4-25.
Figure 4-25 N+N power supply requirements with up to eight nodes installed
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