Ultra M.2 vs SLI/XcrossFire

Trainsmash

New member
Hi, I own a ASRock Z97 Extreme 6. I have been generously donated a Ultra M.2 (PCIe Gen3 x4) SSD, which I am awaiting to install. I am super excited to get this bad boy up and running.

However the point I would like to raise is a theoretical question I am not able to get my head around.
1) The M.2 in question uses the x16 PCIe lane and will drop the GPU to x8. I am not to fussed about this.

2) I have the opportunity to XrossFire my GPU (not a biggy for me yet).

So when you pair GPU it drops to 2 x8, but with the addition of the M.2, will it drop further (e.g x4) or will it happily truck along at 2x8.

Cheer Trainsmash
 
A single GPU as you have it will run at x16

A GPU and the M.2 drive would run at x8/x4

Two GPU's would run at x8/x8

Two GPU's and the M.2 drive when using slot M.2_1 would run at x8/x4/x4


Running a GPU with only 4 lanes will result in a noticeable performance drop, SLI has a minimum requirement of 8 lanes per card as well so technically that may not even work.

The optimal solution to run all 3 in my opinion would be to use the M.2 drive in slot M.2_2 although that will limit it to PCIE2.0 x2 from the Z97 chipset that shouldn't have a huge impact on performance.

JR
 
Ta JR.

Thanks for the answer. In my mind then, just to clarify the XF bit. Would it be possible to run two GPUs in the second and third full PCIe slots at 4x4 and simply sacrifice x16 slot to capitilise on SSD speed.
 
The M.2 uses a Maximum of 4x PCIE 3.0. Putting it in anything above will still only give it x4 speed. Deliberately dropping your GPU speeds below x8 you will see a marked performance drop. M.2 speeds on PCIE 2.0 will still have a speed increase over any SATA 6Gb/s SSD. You are better off having GPU's in the highest bandwidth configuration as possible rather than sacrificing that for an extra speed boost on your drive speed.
 
The performance drop all depends, tbh. I remember when I was using an Asrock 990FX Extreme3 board the slot layout was a bit squiffy and to stop my cards overheating I ended up running then X16 X4. 3DMark Firestrike showed the best score I'd ever seen, yet games were affected differently.

I can't see you specify which GPU you want to Xfire, so it's hard to say. If they are high end cards you may want to get a mobo with a PLX chip that will add more lanes, rather than going X4 X4.
 
Ta JR.

Thanks for the answer. In my mind then, just to clarify the XF bit. Would it be possible to run two GPUs in the second and third full PCIe slots at 4x4 and simply sacrifice x16 slot to capitilise on SSD speed.

Using the M.2 drive in slot M.2_1 would give you the highest SSD speed possible while compromising graphical performance. The 16 lanes from the CPU would be divided between all 3 PCIe devices leaving only x4 for one of the GPU's. With crossfire it would still work and yield better performance than a single card.

Using the M.2 drive in slot M.2_2 would let the drive utilize 2x PCIe lanes from the Z97 chipset instead of the CPU leaving x8/x8 for the graphics cards. PCIE2.0 x2 is still 1gb/s theoreticaly giving you a lot more bandwidth than SATA III.

Either approach will give you more graphical and storage performance than you have currently, personally I would say that using M.2_2 will give you more noticeable benefits.


The only configuration of hardware that wouldn't compromise either would be X79, X99 or Z170 as they have more PCIe lanes available either from the CPU directly or the chipset. However neither is worth the associated cost for that reason alone. Unless you've got two Fury X's and a V-nand NVMe drive I don't think anything will have a radical performance impact.

JR
 
Just to clarify:
MSI HD7950 OCs bought as a pair and seperated between a friend and myself to reduce cost. Friend has upgraded and happy to give the brother back. Hence the enquiry about XF.
SSD = Samsung SM951 M.2.

I ask because it all makes sense, I will buy a higher spec PSU for the XF setup. So far it is a trade off from ultimate performance, but XF seems worth it based on comments.

This is my first real post in the forums and I have to say you guys are awesome. Thanx
 
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