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I am trying to understand the PCI-E principles but I miss something. The reason why I need to understand that is because I working on a project that involve a lot of SATA HDD to be connected to one machine. Because the HDDs are heavy and occupy a lot of space I decided to divide the hosting machine in multiple slaves.
So in my idea one "master" that is equipped with a middle range processor and a mid class motherboard will host 16 HBA PCI-E boards. The "master" server machine have only a SATA SSD for OS and intended to use 4x 1to4 PCI-E riser (splitter) attached to PCI-E slots from motherboard, one riser with his own PCI-E slot.
On the "slave" side we have a computer M-ATX case equipped with 32 HDD, powered by a 650W gold PSU and the riser board with 4 slots of PCI-E equipped with 4 HBA boards. Slave is connected to the master with USB cable provided in the riser package. In theory each PCI-E from the master have 4x HBA cards, and those are connected to 32 SATA HDD.
The idea works until I connect the 4'th slave to 4'th PCI-E. So there is no problem with 3 PCI-E connected with 1to4 PCI-E and host 12 HBA boards (96 HDD). I read about the "lanes" that PCI-E use it, about how chipset and processor use them, but I think I have understood in the wrong way the principle.
I have tried to connect this slave to multiple "master" configurations, and I have used as a master the following configurations:

  • HP Z800 (equipped with dual processor x5675 that intel report it have 32 PCI-E lanes), motherboard used on this system use intel 5200 chipset that reports it can carry 72 PCI-E lanes)
  • HP Z600 (tested before Z800, almost the same config as Z800)
  • Z570 motherboard with Ryzen 5900X (AMD reports 32 PCI-E lanes for processor and 36x usable for AMD chipset Z570)
  • Entry level chipset H110 (6 PCI-E) and B450 (4 PCI-E) with Intel gen 4 and 6 processor.

    All of those configurations fail to boot up to the BIOS when I connect the 4'th slave. Master is powered and on HP six beeps keep report me an error "HP says to check the video card", on the rest of configurations master is power on but there is no signal from video card. I have changed the order of slaves, boards, added another riser between them, powered the risers from the same PSU as the master, more and more, but I believe the problem is a limitation that I don't understood it.

If someone can help me to understand what is happening here and why my setup is not working in this situation, I beg it to do it, because my mind is blowing after 20H of tries. I have attached a picture made in paint, maybe will help to understand the setup.
Thanks !
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