Is having 2 NVME drives worthwhile (based on pcie lanes)

andantecantabile

Junior Member
Oct 22, 2017
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I'm looking at an AMD AM4 motherboard and would like to use 2 NVME drives (one for OS and one for Adobe Premiere files/scratch), but I can't figure out whether I can really get the benefit from them based on motherboard/Ryzen architecture

We can use the ASRock Killer as an example:
https://www.asrock.com/mb/AMD/X370 Killer SLIac/index.asp

There is 1 Ultra M.2 (PCIe Gen3 x4 & SATA3) and 1 M.2 (PCIe Gen2 x2 & SATA3). As I understand, the "Ultra M.2" is suitable for an NVME drive such as Samsung 960, whereas the other M.2 slot will bottleneck drives of that standard.

There is also the issue of PCIe lanes. I understand that Ryzen has 24 lanes, but what exactly does this mean in terms of speed or bottlenecking? Supposing I have a GPU and 1 NVME drive i the "ultra M.2" slot, is it worthwhile getting another NVME for the 2nd M2 or (using an adapter) for the 2nd PCIe 3.0x16? Or is there basically going to be no appreciable difference in speed/performance and I might as well use a 2.5" SATA for my 2nd SSD?
 

Qasar

Member
Nov 18, 2016
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i wonder if Ultra M2 just refers to how many PCIe lanes the slot uses... looking at the board, one slot uses 4 lanes.. aka x4 and the other uses x2, aka 2 lanes if thats the case.. then the m2 x2 slot would only have half the bandwith to use vs the ultra M2 slot, which might be a slight bottle neck ?
i have an Asus X99 deluxe board.. which has one M2 slot, and came with an adapter to put an M2 drive on it.. and plug it into a PCIe slot.. and i compared the 2 with Samsung's Magician software benchmark part.. and so very little difference between the 2 ...
 

andantecantabile

Junior Member
Oct 22, 2017
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i wonder if Ultra M2 just refers to how many PCIe lanes the slot uses... looking at the board, one slot uses 4 lanes.. aka x4 and the other uses x2, aka 2 lanes if thats the case.. then the m2 x2 slot would only have half the bandwith to use vs the ultra M2 slot, which might be a slight bottle neck ?
i have an Asus X99 deluxe board.. which has one M2 slot, and came with an adapter to put an M2 drive on it.. and plug it into a PCIe slot.. and i compared the 2 with Samsung's Magician software benchmark part.. and so very little difference between the 2 ...
Hi Qasar. Yeah I thought about getting that adapter for the full PCIe slot. Maybe I should just get 2 NVME drives and the PCIe adapter, and run some tests.

I read somewhere that the "regular" M.2 slot is basically bottlenecked at a theoretical 8GB/s compared to 16GB/s for "Ultra" M2 or even 32GB/s on some boards/architectures. Obviously that 8GB/s number doesn't compare very favorably with 6GB/s for SATA, however the theoretical maximum and what we actually get are of course massively different. So, thanks for running the benchmark. Not 100% sure but I'm thinking about biting the bullet and then just running the tests. I guess the only reason I'm not is I already have a 512gb 2.5" SSD sitting around, so just not sure there's any reason to pay to upgrade it to NVME. I'm willing to pay if it makes the computer faster, but it seems like there is no solid answer about whether this would be the case.
 

Billy Tallis

Senior member
Aug 4, 2015
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I read somewhere that the "regular" M.2 slot is basically bottlenecked at a theoretical 8GB/s compared to 16GB/s for "Ultra" M2 or even 32GB/s on some boards/architectures. Obviously that 8GB/s number doesn't compare very favorably with 6GB/s for SATA,
These numbers are all wrong. Part of your problem is not understanding that 1GB/s is not the same as 1Gb/s.

A M.2 slot providing four lanes of PCIe 3.0 can support a throughput of almost 4GB/s. This is the maximum achievable through a single M.2 slot. Older (pre-Skylake) motherboards generally had PCIe 2.0 links to their M.2 slots due to limitations of the PCH and its DMI link to the processor. On those older motherboards, the limit would be about 2GB/s for a slot with four PCIe lanes, and 1GB/s for a slot with only two lanes. (Older Intel chipsets didn't offer as many PCIe lanes fanning out from the PCH, so many boards couldn't spare four lanes for the M.2 slot.) The theoretical limit for SATA 3 is 600MB/s, or 0.6GB/s.

ASRock uses the brand "Ultra M.2" for slots with PCIe 3.0 x4 connections, though in this case it'll only operate as PCIe 3.0 x2 if a Bristol Ridge APU is used instead of a Ryzen CPU. The other M.2 slot on this motherboard uses two of the 8 PCIe 2 lanes coming off the X370 chipset.
 
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andantecantabile

Junior Member
Oct 22, 2017
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These numbers are all wrong. Part of your problem is not understanding that 1GB/s is not the same as 1Gb/s.

A M.2 slot providing four lanes of PCIe 3.0 can support a throughput of almost 4GB/s. This is the maximum achievable through a single M.2 slot. Older (pre-Skylake) motherboards generally had PCIe 2.0 links to their M.2 slots due to limitations of the PCH and its DMI link to the processor. On those older motherboards, the limit would be about 2GB/s for a slot with four PCIe lanes, and 1GB/s for a slot with only two lanes. (Older Intel chipsets didn't offer as many PCIe lanes fanning out from the PCH, so many boards couldn't spare four lanes for the M.2 slot.) The theoretical limit for SATA 3 is 600MB/s, or 0.6GB/s.

ASRock uses the brand "Ultra M.2" for slots with PCIe 3.0 x4 connections, though in this case it'll only operate as PCIe 3.0 x2 if a Bristol Ridge APU is used instead of a Ryzen CPU. The other M.2 slot on this motherboard uses two of the 8 PCIe 2 lanes coming off the X370 chipset.
You're right, I didn't spot the errors I made about GB/s vs. Gb/s, I consider myself schooled. Not trying to spread bullshit, I'm just a fairly non-tech-oriented guy who learned basic system-building skills because I like customization and not overpaying for mediocre components or systems. Some of our numbers match after conversion, for example 32Gb/s (4-lane PCIe) is about 4GB/s as you described. Apologies for the conversion error.

Also, from your post I am seeing that even a PCIe Gen2 x2 should be faster than SATA, since even 1GB/s (2 PCIe lanes through M.2) is faster, let alone 2GB/s (4 PCIe lanes). So my 2nd NVME should show performance improvement if put here. If I put it in the PCIe slot with a converter, maybe it will be even faster, since I can use 4 lanes in that slot instead of 2.

Anyway, since Ryzen has 24 lanes, I am thinking my proposed build with 1 GPU and 2 NVME drives on an x370 board should offer notable speed improvement compared to using SATA for my most important drives. If the GPU uses as much as 16, the NVME on "Ultra M.2" uses 4, and the NVME on the second PCIe x16 uses 4, then I'm at 24 and solid.
 
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Qasar

Member
Nov 18, 2016
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even my adapter is only a x4 physical card... if you want full x16 physical, like what a video card has.. then i think i remember seeing an adapter card that has 2 or 4 m2 slots on it.. maybe startech or Asus had it.....

either way.. with my 2 M2 drives.. i have a 960 evo 250 gig as my C drive, and a 500 960 evo as my D drive, OS and games respectfully, and Win10 seems to load a but faster then the 120 gig 850 evo it replaced... my old D: games drive was a 500 gig 850 evo.. and for updating Blizzard games, once the download part was done, and it was changing files around, as well as loading.. specially with SC2, i did notice a speed bump...
 

andantecantabile

Junior Member
Oct 22, 2017
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even my adapter is only a x4 physical card... if you want full x16 physical, like what a video card has.. then i think i remember seeing an adapter card that has 2 or 4 m2 slots on it.. maybe startech or Asus had it.....
More drives might be nice in the future, but I think 2 NVMEs is fine. Our builds are similar in idea, it's just that I plan to use it primarily for Premiere and After Effects (editing workstation), with games as a nice afterthought. Either way, a faster OS plus a faster drive for games/projects seems like a no-brainer for a few extra bucks.

Anyway, with wanting 2 NVMEs, an adapter like you have with x4 is a good idea. The bottleneck on the 2nd drive is twice as high as the 2nd M.2 which only has x2, and I don't see the need for 2 GPUs or any other PCIe devices on this machine. So yeah, the solution works.

I'm still curious if the M.2 with 2xPCIe lanes would offer a serious bottleneck to a 960 Evo for example. But I guess it's academic at this point.
 

Qasar

Member
Nov 18, 2016
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you could always try the m2 drive in both slots, running either samsungs magician benchmark, or another to see if there is a difference...

my comps have always been set up this way.. C: for OS, D : for games : E: misc stoage/odds and ends.. and if present.. F drive to which ever based on need, right now.. i have F for MP3s, G for music vids and 2 more general storage drives, in my main comp... always found it just easier to organize if i have specific drives for things...
 

andantecantabile

Junior Member
Oct 22, 2017
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0
6
you could always try the m2 drive in both slots, running either samsungs magician benchmark, or another to see if there is a difference...

my comps have always been set up this way.. C: for OS, D : for games : E: misc stoage/odds and ends.. and if present.. F drive to which ever based on need, right now.. i have F for MP3s, G for music vids and 2 more general storage drives, in my main comp... always found it just easier to organize if i have specific drives for things...
One thing I just found out in another forum is that some motherboards will cut the PCIe lanes for the PCIe x16 slots if there is something in the other slot. So for example, the motherboard I listed will switch to x8 lanes for the 1st slot if you put an NVME in the 2nd PCIe slot. I have no idea if this would affect GPU performance even at the maximum let alone during normal use, but you might want to check your motherboard for settings like that in future builds. Maybe some more advanced motherboards with good BIOS will let you customize how many lanes to assign to different channels (and in fact, maybe your current motherboard already does that or has different settings than the one I posted)
 

Insert_Nickname

Diamond Member
May 6, 2012
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I'm looking at an AMD AM4 motherboard and would like to use 2 NVME drives (one for OS and one for Adobe Premiere files/scratch), but I can't figure out whether I can really get the benefit from them based on motherboard/Ryzen architecture
Since you're already looking at a pretty high-end AM4 mainboard, might I suggest taking a look at Ryzen Threadripper? You'll never run out of PCIe lanes (60 PCIe 3.0 lanes) with one of those, and even the "low-end" 1900X is a very good performer.
 

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