Reference Material; What Is N+N And N+1 Psu Redundancy; N+N And N+1 Examples - Lenovo x3840 X6 Planning Manual

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Reference Material

What is N+N and N+1 PSU Redundancy

N+N PSU redundancy is where N is the minimum number of PSUs needed to keep the
system operational, plus N number of PSUs again for redundancy. Essentially, the
number of PSUs are double of what is necessary to keep the system operational.
N+N is needed when a system needs to be power source redundant (See example
diagrams in "Typical PDU Configurations" above).
N+1 PSU redundancy is where N is the minimum number of PSUs needed to keep the
system operational, plus one PSU for redundancy. N+1 is used when a system needs
only to tolerate a single PSU failure and stay operational (See example diagrams in
"Typical PDU Configurations" above). Think of N+1 as having one PSU as a hot
spare.

N+N and N+1 Examples

Notice in the N+1 diagrams below that there are two sources. Typically, N+1devices
would be connected to one power source since N+1devices do not derive any benefit
from two power sources. It is shown here with two power sources to demonstrate
this lack of benefit for N+1devices.
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