Issues after installing 5th graphics card

[rgeorgy]

Hello,

I've managed to run 4 graphic cards so far with this setup.

- Motherboard: Asus Prime Z270-p
- 4 x GTX 1060 3G (ultimately need to install 6)
- RAM: 8 GB
- Intel pentium 1151
- EVGA SuperNOVA 1050 GS, 80+ GOLD 1050W
- Cards are connected via powered risers

Relevant software
- Ubunutu 17.04
- Latest Nvidia binary driver 281


I know that installing 4+ cards is usually problematic in Linux. I've been following the instructions in https://bitcointalk.org/index.php?topic=1917749.0 and they helped me install 4th card. However, the instructions are extremely indeterministic and don't have a clear order. They usually involve:

- Turn on/off Bios "Above 4G decoding".
- Change PCIE link speed to Gen 1, 2 or 3.
- Change DMI Max Link Speed to Gen1, 2, or 3.
- Add one card at a time.

Once I install 5th card into motherboard and turn on computer, I get one of the following issues:

- Ubuntu boots fine but "nvidia-settings" only shows 4 cards
- BIOS splash appears but black screen afterwards.
- No output signal at all.
- No BIOS splash appears. I just get the error:

Error: unknown filesystem.
grub rescue>

Random questions I have:

- Does it matter which card has HDMI plugged? Should I rely on the integrated intel gpu instead?
- When people say "install one card at a time, then install drivers", aren't drivers already installed?
- There are 6 PCI-E slots 1) PCI-E x16 (x16 mode), PCI-E x16 (max x4 mode) and 4*PCI-E x1. Do they differ in anyway? Is there supposed to be an inherently primary slot?

I realize I'm completely lost and can't make sense of what I'm seeing. But that's why I'm here! I'd really appreciate any debugging tips.

Thank you

[Rostyk1993]

I have the same problem but with Windows.
I can just run 5 cards. I tried everything to make work the 6th card. Next step maybe windows in UEFI mode. Or riser duplicator 1×2.

[Rmcdermott927]

Can you get a meter to see how much power your PC is drawing at the wall to rule out PSU issues?

[Rostyk1993]

corsair hx1200i