Question Thoughts on bifurcating RTX 4090 bandwidth due to PCIe 5.0 SSD?

[HungryHamster]

I'm trying to decide whether it's worth it to get a Samsung 990 pro PCIe 5.0 SSD considering it will steal lanes from my RTX 4090. I was told the following:

"The only way to get a Gen 5 SSD on a LGA 1700 CPU is to steal lanes from the GPU. In order to get a Gen 5 slot, it would have to bifurcate the PCIe slot the GPU is using, reducing it down to 8 lanes and using those 8 lanes to go to an M.2 slot.”

And there's a nice article that shows some differences in scaling performance here: https://www.techpowerup.com/review/nvidia-geforce-rtx-4090-pci-express-scaling/

tldr: While for old games the difference is pretty much negligible, for newer, modern DX 12 games you might lose 5-10 FPS if you bifurcate the PCIe 5.0 slot.

My current thinking is that it’s still going to be a while before PCIe 5.0 SSDs are useful in games because Direct Storage still hasn’t been implemented very much. As someone who is building a new computer only for gaming it would then seem more beneficial to just get a PCIe 4.0 SSD instead and avoid potentially losing FPS especially in newer titles.

Anyways, I'm just wondering what your thoughts are. Are there other considerations I should have? I'm just trying to fully weigh the pros and cons of either option.

 

[Math Geek]

what exact motherboard do you have? would be rare for a single m.2 drive to take lanes from the main pcie slot. usually you only lose lanes if you use every pcie slot, but i have seen some more budget motherboards that will take lanes from the secondary pcie slot(s).

need to know what exact motherboard you have so can check it's specs. i would be very surprised if you lose any lanes from the main pcie slot with an m.2 drive installed.

 

[HungryHamster]

what exact motherboard do you have? would be rare for a single m.2 drive to take lanes from the main pcie slot. usually you only lose lanes if you use every pcie slot, but i have seen some more budget motherboards that will take lanes from the secondary pcie slot(s).

need to know what exact motherboard you have so can check it's specs. i would be very surprised if you lose any lanes from the main pcie slot with an m.2 drive installed.

Thanks for your response. The motherboard is the ASUS ROG Maximus Z790 Hero.

I don't think it matter which motherboard it is, though. From the article:

"both the 12th Gen and upcoming 13th Gen Core "Raptor Lake" put out PCIe Gen 5 only for the x16 PEG slot, the CPU-attached NVMe slots are still Gen 4. In order to not lose this platform advantage to AMD, Intel is now allowing motherboard designers to add Gen 5 M.2 NVMe slots on their upcoming 700-series motherboards, but they're going about this by stealing PCIe lanes from the x16 PEG slot. This means that when 13th Gen Core users install an SSD in that M.2 slot, it will redirect eight lanes that were used by the x16 graphics slot, and use those on the M.2 slot. So those building a bleeding-edge Core i9-13900K + RTX 4090 gaming PC with a Gen 5 NVMe SSD will have to content with the RTX 4090 running at PCI-Express x8 bandwidth."

 

[Math Geek]

man that is a headache to decipher.

it appears the m.2 slots on the mobo are all pcie 4, and like i thought they do not take lanes from the main pcie slot.

the only way to get pcie 5 ssd is with the "hyper m.2 card" that seems to be included.

it appears to me that if you use 2 pcie slots, one for the gpu and one for this m.2 card, then it does split the slots to x8 each. and for that you get a single pcie 5 m.2 slot (the second slot on the card is disabled when using a 5.0 ssd)

i don't see a way around it. considering there is almost no real world difference between pcie 4 or 5 ssd's, it would not be worth losing the lanes if you lose performance of the very expensive 4090 card. i'd stick to a 4.0 ssd in the normal m.2 slot and get all the lanes all around.

anyone feel free to check out the manual and see if i misinterpreted, but this is how i am reading it

https://dlcdnets.asus.com/pub/ASUS/..._HERO/E20592_ROG_MAXIMUS_Z790_HERO_UM_WEB.pdf

 

[Karadjgne]

In a word, No.

 

[HungryHamster]

man that is a headache to decipher.

it appears the m.2 slots on the mobo are all pcie 4, and like i thought they do not take lanes from the main pcie slot.

the only way to get pcie 5 ssd is with the "hyper m.2 card" that seems to be included.

it appears to me that if you use 2 pcie slots, one for the gpu and one for this m.2 card, then it does split the slots to x8 each. and for that you get a single pcie 5 m.2 slot (the second slot on the card is disabled when using a 5.0 ssd)

i don't see a way around it. considering there is almost no real world difference between pcie 4 or 5 ssd's, it would not be worth losing the lanes if you lose performance of the very expensive 4090 card. i'd stick to a 4.0 ssd in the normal m.2 slot and get all the lanes all around.

anyone feel free to check out the manual and see if i misinterpreted, but this is how i am reading it

https://dlcdnets.asus.com/pub/ASUS/..._HERO/E20592_ROG_MAXIMUS_Z790_HERO_UM_WEB.pdf

Thanks for your input. That's pretty much the conclusion I came to as well.

 

[Math Geek]

as a side note it looks like the last pcie slot would not take the lanes from the first slot. it looks to be x4 either way. but that slot with the m.2 card is only pcie 4 which is not worth the trouble considering there are 3 m.2 slots on the board that are already pcie 4.

 

[Karadjgne]

It's called 'The Point of Diminishing Returns' and NVMe basically reached it a long time ago. Game files are small enough that their speed of transmission to the ram is in nanoseconds at best, outpacing the cpu's demand. For simplicity, if the cpu only took a game file every second from the ram, it makes no difference if the next file is shipped to the ram in half a second, or quarter of a second, it's still got a full second waiting period.

It's why for games, even Sata ssds are basically the same. There's only one time NVMe really pays off vs Sata, or Gen4 over Gen3 and that's in large file transfers, like downloading a full game of 50+Gb or legal documents, books etc. Any file that approaches exceeding the size of the ram where the throughput time at the ram exceeds the demand time from the cpu.

So chopping the 4090 Gen5 x16 to 4090 Gen4 x16 is a loss of possible performance for no real advantage to the NVMe. And as NVMe gets faster, ram gets faster, cpus get faster, the physical time differences get smaller to the point of being no different.

Hdd to Sata, big time change. Nvme to nvme? Ehh.

 

[HungryHamster]

It's called 'The Point of Diminishing Returns' and NVMe basically reached it a long time ago. Game files are small enough that their speed of transmission to the ram is in nanoseconds at best, outpacing the cpu's demand. For simplicity, if the cpu only took a game file every second from the ram, it makes no difference if the next file is shipped to the ram in half a second, or quarter of a second, it's still got a full second waiting period.

It's why for games, even Sata ssds are basically the same. There's only one time NVMe really pays off vs Sata, or Gen4 over Gen3 and that's in large file transfers, like downloading a full game of 50+Gb or legal documents, books etc. Any file that approaches exceeding the size of the ram where the throughput time at the ram exceeds the demand time from the cpu.

So chopping the 4090 Gen5 x16 to 4090 Gen4 x16 is a loss of possible performance for no real advantage to the NVMe. And as NVMe gets faster, ram gets faster, cpus get faster, the physical time differences get smaller to the point of being no different.

Hdd to Sata, big time change. Nvme to nvme? Ehh.

Thanks for your detailed response. The one thing that seems might be important for SSDs as they relate to gaming performance is Direct Storage:

"Current game engines don't utilize multi-core data streaming from storage much, if at all. It's CPU (mostly) & memory bandwidth bound, once you get to SSD speeds. Current API never needed it, and especially on PS4/Xbox 1, where the HDD is so slow that trying to do multi-stream fetching will stall it anyway, so it was never a focal point for devs. This is where Direct Storage IO and new consoles change the landscape, expect game engines to be revised for these new standards in the near future."

That said, direct storage was highly promoted when the PS5 first came out over 2 years ago and it has yet to be implemented much at all. As such, I agree with you that it's probably not worth getting a PCIe 5.0 SSD that will cut into my graphics card performance, but as someone who is trying to build a computer that will last the next 5 years it's a little bit worrisome that perhaps devs will finally implement this feature that will heavily rely on SSD performance.

 

[Math Geek]

there is no way to build something today that will guarantee compatibility with tech years from now. direct storage is not going to revolutionize gaming all of a sudden a couple years from now.

this along with many other "features" are simply selling points designed to make you do exactly what you are doing. buy something you don't need "just in case" this new feature is all of a sudden the thing to have. look back and ask yourself how many other times has this actually happened.?

i'd not worry about 5 years from now until it gets here. all you can do is get the best for your needs now and deal with that when it comes.

also keep in mind storage spaces is basically software raid and requires multiple drives combines to see its benefit. you only have the option for a single 5.0 ssd anyway so you'd be pairing it with a 4.0 drive in the m.2 slot just to use the feature if it shows up. 2 4.0 drives would show a nice boost either way. so again another reason not to worry about it and just go with the 4.0 drive