Problem with dual mining rig Sapphire 580RX Nitro+ Different hash rates! Help

[mealmighty]

Hi i have two identical Sapphire 580 RX Nitro + 8GB with Samsung memory in a rig with Asus Prime Z270-P Mobo
I have flashed their bioses with an optimised one and each one of them individually gets 30.8 Mh/s but when both are together one always underperforms and drops to 22Mh/s.

http://prntscr.com/hubno5  <--- screenshot

I tried troubleshooting this by switching the connectors and raisers to each card and also switching their positions on the mobo but each of them in any combination individually gets the max rate but when both together one drops hash rates from 30.8 to 22!

Any idea what could be the problem? I plan on getting 4 more of those and i am afraid if i dont know whats causing this i am about to be in big trouble when i have to run 6 of them and get several of them underperforming.

Regards,
Atanas

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[mealmighty]

Forgot to mention that i am running on a Windows 10 Home edition.

[leonix007]

I tried troubleshooting this by switching the connectors and raisers to each card and also switching their positions on the mobo but each of them in any combination individually gets the max rate but when both together one drops hash rates from 30.8 to 22!

isolate one by one, First use the riser with low hashrate on main PCI-e, install one GPU, if it has no prob, install the second GPU if still drops hashrate, check if OC settings has been took effect to both GPU's, I am not sure with overdrive tool, but in MSI AB it has an option that a separate settings could be applied to each GPU even its identical.

[mealmighty]

isolate one by one, First use the riser with low hashrate on main PCI-e, install one GPU, if it has no prob, install the second GPU if still drops hashrate, check if OC settings has been took effect to both GPU's, I am not sure with overdrive tool, but in MSI AB it has an option that a separate settings could be applied to each GPU even its identical.

I tried that and individually each card gets 30.8MH/s but when paired together one of them gets 22MH/s
The fault is not in the raisers. The OC settings has not changed on either card.

From GPU-Z i see that each card clock and memory settings are the same but on the underperforming card that hashes with the lower rate i see that Memory Controller Load is at only 75% where on the one that hashes at max speed it is at 100%

What is preventing the second card from reaching its max memory load?

[Njeroe]

Hi i have two identical Sapphire 580 RX Nitro + 8GB with Samsung memory in a rig with Asus Prime Z270-P Mobo
I have flashed their bioses with an optimised one and each one of them individually gets 30.8 Mh/s but when both are together one always underperforms and drops to 22Mh/s.

http://prntscr.com/hubno5  <--- screenshot

I tried troubleshooting this by switching the connectors and raisers to each card and also switching their positions on the mobo but each of them in any combination individually gets the max rate but when both together one drops hash rates from 30.8 to 22!

Any idea what could be the problem? I plan on getting 4 more of those and i am afraid if i dont know whats causing this i am about to be in big trouble when i have to run 6 of them and get several of them underperforming.

Regards,
Atanas

Have you disabled CrossfireX for them? that could cause hashrate drop for 2 GPUs...