Is There a GPU Limit For Motherboards (Not Related to Physical Slots)

Edit: Solution in post #4

I find this odd, so I have come to this conclusion; my motherboard only allows 3 active GPU's/video cards (which I could be wrong, but I don't think I am edit: I was SO wrong!  ).

My board, ASRock Z97 Extreme 4

I have 3 16X (length, not wired) slots, and 3 X1 slots (all PCIe).

My setup is as follows for the 16X's:

GT720, GT720, Adaptec1430SA.

I have the onboard outputting the console, and 2 VM's regularly running.

I have a 5450 that I cut down to be a 1X card (it met my die grinder!), card works fine in my other PC.

Doesn't come up in UnRaid BIOS doesn't list anything in the slot (ASRock has a system viewer that will list which slots have a card).

I have another GT720 and one of my 1X slots has the back removed from it (it met the fate of an old soldering iron).

The slot works fine, used with a 1X NIC for a long time.

This is also not recognized in unRAID nor in the BIOS.

The fan on this card is also not spinning!

I am not certain this card works, as I've never used it, but I'm pretty sure it does.

So............. Does anyone know if a MB can have a 3 GPU limit?

It would be the maximum amount for an SLI/Crossfire setup with most configurations.

The fact that the fan is not spinning and I know the slot works, combined with my modified 5450 not working in any 1X slot I have (and the fact it works fine in my main computer) makes me think this is the case.

I have a way to figure this out, by removing my 1430SA and adding in the GT720 to make sure it is not my hackery (I am doubting this, but worth a test).

If so I may be able to get 3 usable for VM's and disable the onboard GPU and then steal the output from the console.

However this still presents that 3 limit, and I actually had plans to eventually get to 4 discrete VM's that would preferably always be available and on.

It sounds like this may be the case (good Ol' mining people and their need for like 6 GPU's!).

I don't know if my board specifically has the issue, but some other have had issues with more than 3 cards initializing.

https://litecointalk.org/index.php?topic=728.0

I thought it could be power related (550W PSU) however I have noticed zero other issues, adding the 3rd just never works.

The GPU's I have are pretty light on power requirements, but I understand I am getting close to needing to up it.

Molex header on the MB is correctly attached (in case I am maxing out available power on the PCIe bus, as none of these GPU's take an external 12V power connector).

Edit: The lack of fan spinning on the GT720 is making me think about this more, as I doubt the MB has any control over this. I'm thinking the 1X slots on my motherboard do not supply enough current to run a GPU off of. I will either mod my 5450 with a molex connector (or GPU powered 12V header), or buy a powered 1X to 16X riser card (typically has a molex connector for power) to see if that solves the issue. I'm thinking it will, but will update as I figure it out.

I likely need to do this (short pin A1-B17 for 1X PCIe to work):

https://bitcointalk.org/index.php?topic=102547.msg1124000#msg1124000

https://bitcointalk.org/index.php?topic=36061.0

Will update if this resolves my issue.

This was simple enough to fix, but wouldn't have a clue without doing some research into it (thanks bitcointalk)!

If you didn't know this, PCIe spec allows cards to be used in various configurations/lanes. So a 16X card can be operated in 16X, or 8X, or 4X, or 1X mode.

The pins are wired to allow for this, you just need to "make it fit" or however you choose to do that.

For HD decoding for a HTPC, you don't need the bandwidth provided by the higher lane count, 1X is more than sufficient.

If you want to use a 16X card in a 1X slot, you have a couple of options.

1)Buy a proper 1X video card and pay the premium that they command (it's not THAT much more, options are however limited).

2)Buy a riser/extension card that goes from 16X to 1X, however you now need to mount the card somewhere else (as it is now higher than it should be)

3)Modify a 1X slot by removing the back of it to allow a larger card than the slot

4)Modify the card by cutting it down to fit into the 1X/4X slot you want to use (likely the least preferred option, once you cut the card you can't uncut it!).

If you choose options 2-4 your motherboard may require you to short out the "enable" pin for the card to be recognized.

In my understanding of this, a 16X card would have this wired further in the slot at some point in the 4X/8X/16X length of the slot.

If you cut the card, modify the slot, or buy a riser extension, this "enable" will not be made and the card may not be recognized.

Some MB's don't require shorting of the pin, so you may not have to perform this (this enable has something to do with hot plugging, look into it if you want to know more).

I had a combination of option 3 & 4, and neither card would be recognized. I also have a riser/extension (they are dirt cheap) however prefer to be able to mount the card in the normal way.

So if you do any of the above and the card doesn't come up as recognized in UnRAID (or more importantly in the BIOS if you have a way to check) you may need to short the enable pin.

This is pretty simple to do, and if completing this on the slot, a Cat5e solid piece of wire is a great gauge to use.

You can also short these pins on the card itself if you prefer, it really makes zero difference.

Short out pins A1 to B17 (See pic: 1st pin on longer left back part of slot, to 2nd to last pin on shorter right side of slot away from the back of the case), insert card, fixed!

I now have 4 available cards to use for VMs!

See pics, it may not be the prettiest thing, but solved my issues instantly.

@jonp this may not be something too many people choose to do, nor exactly "recommended", however it may be helpful to mention this trick somewhere (Wiki, guide, etc...) for people who may want to use a 1X slot for a card they have lying around. It is certainly a bit "hackish" however not everyone here is exactly running a business grade/commercial server with their UnRAID setup.

Hope this information helps someone.

Wow, an extremely interesting read. Just shows the ingenuity of people here on the forums. Thanks for info.

Wow, an extremely interesting read. Just shows the ingenuity of people here on the forums. Thanks for info.

Thanks!

It was frustrating, and I was determined... 

I use a low profile sff card with the 16x ->1x adapters and they fit and can be screwed down.

Hey bungee91,

do you think this might fix my issue?

http://lime-technology.com/forum/index.php?topic=39954.msg467996#msg467996

I wonder if this mod will cause issues when no graphics card is plugged in the PEG slot?

I just need the PCI card to work.

Hey bungee91,

do you think this might fix my issue?

http://lime-technology.com/forum/index.php?topic=39954.msg467996#msg467996

 

I wonder if this mod will cause issues when no graphics card is plugged in the PEG slot?

I just need the PCI card to work.

I have no clue what this may do without an actual card installed.. I suppose it wouldn't hurt to try, however I take no responsibility in that assessment. If you do attempt, report back with the outcome.