MP 1,1-5,1 AMAZING NEWS - 2.5 Width GPUs will never again interfere with SLOT 2

zedex

macrumors member
Oct 21, 2018
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Perth, WA
A picture paints a 1000 words..

RADEON RX 480 SINGLE SLOT PCIE (x4) Z1.JPG


First - turn your double-width bracket in to a single-slot (cost AUD 25)

RADEON RX 480 SINGLE SLOT PCIE (x4) Z2.JPG


This image shows that almost ALL 2.5 width cards can be cleanly installed in SLOT 4 (total clearance above a standard double-slot like the RX480 pictured is 15mm)

..with that said - just start to think about the possibilities for your cMP now that you have 32 lanes of NVME storage potential ready for installation in Slot 1 and Slot 2(!!)

RADEON RX 480 SINGLE SLOT PCIE (x4) Z3.JPG



Summary of the (less obvious) POSITIVES..
[1] GPU heat no longer affects thermally sensitive PCIe components installed immediately above it (like bifurcated NVMe HBA installations)
[2] Ready (now) for the creation of scratch disks that can comfortably handle SUSTAINED data read write speeds of 10-12 Gbps (2x squids or equivalent required).
[3] Optimal PCIe bandwidth saturation (for more information - see my drunken post on maximising PCIe lanes usage HERE: Mac Pro 2019 - PCIe Expansion Opportunities?

Summary of the (mostly obvious) NEGATIVES..
[1] This solution heavily restricts access to the SATA II Bays 3-4 (SATA extension cables MAY still be used in some cases - no access with a 2.5 width GPU)
[2] Many of the non-reference cards will have a completely unusable/inaccessible DVI port after the double-slot bracket is machined in half (to create the "no aesthetic compromise" single-slot bracket depicted in the first image).
[3] While all current generation GPUs typically use 4 lanes of bandwidth in 95% of use cases. Future graphics card bandwidth requirements will probably reach 200% lane saturation on a PCIe 2.0 (x4) slot by 2022.

I look forward to seeing some phenomenally powerful new configs based on the vast new options that fall out of the bottom of this approach -- PLEASE SHARE PICTURES and INSPIRE OTHER MEMBERS..!
 
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sailmac

macrumors 6502
Jan 15, 2008
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Hmm, this is interesting.

You mentioned this interferes with access to SATA bays 1-3. I'm thinking you meant bays 2-4? Because bay 1 is closest to the front of the machine.

I'm interested in visualizing just how much your GPU is encroaching on the SATA bays. You stated 15mm clearance above a standard 2-slot GPU (e.g. your RX 480) but seeing would be helpful. If you have time and it's not a hassle, please will you post additional photo(s) showing the insides but from further away so we can get the big picture?

Also, is the single-wide bracket you're using a re-creation patterned on the stock double-wide bracket, or is it the actual stock double-wide bracket simply cut in half by a machine shop? I'm guessing the latter and, if so, I'm surmising someone not interested in aesthetics could probably do this at home.

For reference-type GPUs with blowers I believe your method is something to think about. I anticipate limited space beneath the SATA bays may starve open-air cooler GPUs.
 

Pval

macrumors member
Jan 7, 2008
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Holland
GPUs don’t really need x16 slots, they only do primarily because the PCIE spec only allows x16 slots to go up to 75W.
Regarding performance, lower resolutions will be affected more. That’s because the GPU can process lower resolutions faster, thus you need to feed it scene data faster to fully utilize it, which will be hampered by the x4 slot.
 
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zedex

macrumors member
Oct 21, 2018
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Perth, WA
Hmm, this is interesting.

You mentioned this interferes with access to SATA bays 1-3. I'm thinking you meant bays 2-4? Because bay 1 is closest to the front of the machine.

I'm interested in visualizing just how much your GPU is encroaching on the SATA bays. You stated 15mm clearance above a standard 2-slot GPU (e.g. your RX 480) but seeing would be helpful. If you have time and it's not a hassle, please will you post additional photo(s) showing the insides but from further away so we can get the big picture?
Hi @sailmac - you are correct in respect of the SATA bays numbering - I'll go back and edit it in a moment..

I have uploaded 2 more photos to address your questions on headroom (between the case ceiling and the position of the RX-480) and access to the SATA bays..

RX480-SATA.JPG


In short - the SATA bays are clearly accessible (using the SATA extension cables pictured) but ONLY when the GPU is standard double width. By contrast - the SATA interface would NOT be accessible (BAYS 3-4) if you install a 2.5 width GPU.

RX480-15MM.JPG


I should add that the original bracket was taken to a metal workshop where they cut the bracket in half. I tested it first without the bracket - fully functional but aesthetically unsatisfying.
 

sailmac

macrumors 6502
Jan 15, 2008
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Thank you for taking time to post additional photos and giving those extra details!
 

Lenny_

macrumors newbie
Aug 28, 2018
28
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Europe
That is an interesting idea. I had no clue that slot 3 or 4 would be of any use for GPUs.
As I didn't use slot 4 so far ... I installed a 2nd GPU.

For comparison: here is the result, just one GPU in slot 1:
1GPU.png


...and here is the result with the 2nd GPU in slot 4:
2GPUs.png


That is much better than I expected it to be. Prior to this experiment I already thought I had maxed out my Mac Pro more or less to the limit. Now it's becoming a growling monster ;-)
 

zedex

macrumors member
Oct 21, 2018
98
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0
Perth, WA
Hey dude - really appreciate those benchmarks - particularly given that you have 2 high-end recent release GPUs to showcase the potential still to be tapped from this legendary piece of hardware. Looks like you're well on the way to maximising PCIe lane usage with that SSD7101 in the mix.

VERY VERY NICE!

Quick question - which macOS version/build did you run these tests on..?
 
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