When using two FUP8X25S3HSDK in an Intel P4000M chassis, I know the two cages need to be joined together by a cable with one I2C in connected to the others I2C out.
Does it matter which cage, upper or lower is cabled to the motherboard? The motherboard in question is the Intel S2600CW.
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It's usually recommended to cable the lower one first nevertheless there should not be issues the other way around as long as the cables have enough length.
Intel Customer Support Technician