Optimum power redundancy can mean different things depending on the external power configuration provided to the PDUs. Under the covers, each PSU contains two 1800W power trains. When both line cords are connected, the PSU can support the full 3600W, but if only a single line cord is functioning, the PSU will only support 1800W. Each PSU is connected to the midplane, so the two power trains within each PSU are shared, and the two PSUs in the enclosure are also shared. Think of this as having 4×1800W of total available power to the system. System power requirements can range from a low level (<1800W) to a high level (>2800W) depending on the configuration, and the PSUs will provide power as long as there is sufficient capacity to do so. So if the configuration requires less than 1800W, the system could technically lose up to three line cords and continue to run.
The client's external power configuration will also play a factor here, as there are multiple different power topologies. For example, a single-phase connection to two different PDUs - PDU A and PDU B - could be set up so that PDU A connects to PSU 1 and PDU B connects to PSU 2, similar to how an FS7300 works today. Alternatively, this configuration could split each PDU's power across both PSUs, so that A1 and B1 connect to PSU 1, and A2 and B2 connect to PSU 2. This split arrangement can provide additional redundancy. However, if both PDU A and PSU 1 were lost, the system would only have access to 1800W of total power, and if the system requires more than this, it would not remain online.
This can be further extended to three-phase PDUs, where each PDU has A, B, and C outputs, and each PDU line cord connects to a different phase - for example, A1/B1 to PSU 1 and B1/C1 to PSU 2. If two independent three-phase power subsystems are available, further redundancy can be achieved by connecting each PSU to independent phases from each source - for example, A1/B1 to PSU 1 and A2/B2 to PSU 2. There are multiple additional configuration examples beyond these.
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Brent Yardley
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Original Message:
Sent: 09/03/26 12:37 PM
From: Barry Smith
Subject: FS7600 correct PSU feed cabling
Although the though of connecting a power supply to both pdu will give you redundancy IBM does not recommend this for a couple of reasons
If both PSUs are connected to both power circuits and one power circuit fails, it's not possible to hot swap a PSU until power is restored
If there was a power surge from 1 of the pdu both power supplies could be affected both you will need to actually power the system down to replace .
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Barry Smith
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Original Message:
Sent: 09/03/26 10:28 AM
From: Uwe Schreiber
Subject: FS7600 correct PSU feed cabling
Hi Stuart,
by connecting both inlets of a PSU to a single PDU (e.g. PSU-1 => PDU-A and PSU-2 => PDU-B)
you can not survive losing a PDU and a PSU (e.g. PDU-A and PSU-2)
By connecting each PSU to both PDUs you cover that type of "double failure".
Most redundancy is provided by connecting the inlets of both PSUs to 4 different PDUs.
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Uwe Schreiber
System Engineer / Solution Architect
SVA System Vertrieb Alexander GmbH
Wiesbaden
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