Z370\X299

[Tom MM]

Hey

Will putting 2 M.2 SSD one for the OS and the other for fast storage bottleneck the DMI link to the CPU on Z370?

If so what is the point of more then one M.2 slot on a Z370 Motherboard?

 

Thanks

[Simon771]

11 minutes ago, Tom MM said:

Hey

Will putting 2 M.2 SSD one for the OS and the other for fast storage bottleneck the DMI link to the CPU on Z370?

If so what is the point of more then one M.2 slot on a Z370 Motherboard?

 

Thanks

Z370 chipset have 24 PCI-e lanes and Coffe lake CPUs have 16 of those.

So 16 from CPU will be used for GPU, and the rest 24 can be used for your M.2.

If I'm not mistaken M.2 will use x4, so you can put more M.2 SSDs and it still should be fine.

 

Or am I missing something?

[Master Disaster]

22 minutes ago, Simon771 said:

Z370 chipset have 24 PCI-e lanes and Coffe lake CPUs have 16 of those.

So 16 from CPU will be used for GPU, and the rest 24 can be used for your M.2.

If I'm not mistaken M.2 will use x4, so you can put more M.2 SSDs and it still should be fine.

 

Or am I missing something?

Z370 has 40 PCIe lanes and the CPU uses 16 of them.

 

https://www.tweaktown.com/news/59247/intel-coffee-lake-flagship-8700k-cpu-40-pcie-lanes/index.html

 

Never mind, you were indeed correct. Z370 has 24 PCIe lanes, I don't know what Tweaktown was reporting on lol

 

https://ark.intel.com/products/125903/Intel-Z370-Chipset

 

 

[dizmo]

Are you getting NVME or SATA SSDs?

Personally I wouldn't bother getting two. Just get one larger one. Unless for some reason you want differentiation, but why wouldn't you just partition them at that point.

 

Welcome to the forum

 

 

34 minutes ago, Simon771 said:

Z370 chipset have 24 PCI-e lanes and Coffe lake CPUs have 16 of those.

So 16 from CPU will be used for GPU, and the rest 24 can be used for your M.2.

If I'm not mistaken M.2 will use x4, so you can put more M.2 SSDs and it still should be fine.

 

Or am I missing something?

You're assuming he's using NVME drives.

14 minutes ago, Master Disaster said:

Z370 has 40 PCIe lanes and the CPU uses 16 of them.

 

https://www.tweaktown.com/news/59247/intel-coffee-lake-flagship-8700k-cpu-40-pcie-lanes/index.html

 

Never mind, you were indeed correct. Z370 has 24 PCIe lanes, I don't know what Tweaktown was reporting on lol

 

https://ark.intel.com/products/125903/Intel-Z370-Chipset

That's just for the CPU. You get more lanes from the chipset.

[SnowyMus]

52 minutes ago, Tom MM said:

Hey

Will putting 2 M.2 SSD one for the OS and the other for fast storage bottleneck the DMI link to the CPU on Z370?

If they were both PCIe drives and you were running both of them at maximum bandwidth at the same time, sure.

 

Quote

If so what is the point of more then one M.2 slot on a Z370 Motherboard?

The point of more than one M.2 slot is to allow you to use more M.2 drives at once. Even if you had only one PCIe lane of bandwidth for a device, it'd be faster than SATA III, and you probably won't be tapping out the entire interface at once all of the time.

 

39 minutes ago, Simon771 said:

Z370 chipset have 24 PCI-e lanes and Coffe lake CPUs have 16 of those.

So 16 from CPU will be used for GPU, and the rest 24 can be used for your M.2.

If I'm not mistaken M.2 will use x4, so you can put more M.2 SSDs and it still should be fine.

 

Or am I missing something?

The question was whether or not the DMI interface would bottleneck two M.2 devices. The issue is that, while the chipset does have 24 PCIe lanes, it only has four lanes of bandwidth to the CPU, and these four lanes also contend with interfaces like SATA, USB, and Ethernet.

 

20 minutes ago, Master Disaster said:

Z370 has 40 PCIe lanes and the CPU uses 16 of them.

 

https://www.tweaktown.com/news/59247/intel-coffee-lake-flagship-8700k-cpu-40-pcie-lanes/index.html

As a platform, technically yes.

 

The Z370 chipset has 24 lanes. - https://ark.intel.com/products/125903/Intel-Z370-Chipset

Intel CPUs have 16 lanes - https://ark.intel.com/products/126684/Intel-Core-i7-8700K-Processor-12M-Cache-up-to-4_70-GHz

 

If you do the math, 16 + 24 = 40. 16 lanes on the chipset aren't entirely equal to the 16 lanes on the CPU, though.

[Simon771]

11 minutes ago, Kavawuvi said:

The question was whether or not the DMI interface would bottleneck two M.2 devices. The issue is that, while the chipset does have 24 PCIe lanes, it only has four lanes of bandwidth to the CPU, and these four lanes also contend with interfaces like SATA, USB, and Ethernet.

So the problem could be if someone would be using 2x NVMe M.2 SSD in raid that would acctually use 8 PCI lanes from chipset, but it would be able to communicate with CPU by 4 PCI lanes link. In that case performance would be more like if each M.2 would run on x2 PCI lanes?

[SnowyMus]

10 minutes ago, Simon771 said:

So the problem could be if someone would be using 2x NVMe M.2 SSD in raid that would acctually use 8 PCI lanes from chipset, but it would be able to communicate with CPU by 4 PCI lanes link. In that case performance would be more like if each M.2 would run on x2 PCI lanes?

Maybe. You can be sure your drives won't perform optimally if they are starved for bandwidth. However, just because a device has a PCIe x4 interface doesn't mean it will use all of its available bandwidth all the time, so I guess it really just depends.

 

For NVMe RAID, you may just be better off going with Threadripper or Skylake-X, as those CPUs have a lot more lanes, but again, it depends.

[Simon771]

1 hour ago, Kavawuvi said:

Maybe. You can be sure your drives won't perform optimally if they are starved for bandwidth. However, just because a device has a PCIe x4 interface doesn't mean it will use all of its available bandwidth all the time, so I guess it really just depends.

 

For NVMe RAID, you may just be better off going with Threadripper or Skylake-X, as those CPUs have a lot more lanes, but again, it depends.

Well I ordered Z370 and i5 8600k few days ago.

I don't think I will experience any problems with single samsung 960 m.2 ssd

[Tom MM]

How will it work if the SSDs are not in RAID? 

Each of them would be using X4 and and fill the DMI link one at a time?

Would it be better then to take the i7 7820X instead of the i7 8700K?

I'm on the fence about which one to take for my new build, the i7 7820X is about the top of what i'm going to spend on a cpu.

The i7 8700K is what i wanted to go with, but if it's going to bottleneck the SSDs than that could be a problem.

I currently prefer intel since i'm not so comfortable with AMD cpu's at the moment and I postponed this build long enough maybe on my next build.

 

Thank you very much ^^

[SnowyMus]

6 hours ago, Tom MM said:

How will it work if the SSDs are not in RAID? 

Each of them would be using X4 and and fill the DMI link one at a time?

The interface you use isn't going to determine how much bandwidth it'll use. For instance, if you were to plug in a 5400 RPM hard drive into a SATA III 6 Gbps port, while it has a 6 Gbps interface, it's not going to be using nearly that much of its maximum bandwidth. In fact, it's possible may not ever use much more than half of it. It's the same way with NVMe: if your drive is idle, then it's not going to use any bandwidth because it's idle. If your drive is reading at full speed, it may not necessarily be running at 32 Gbps, either. This means that having two drives connected isn't going to necessarily limit their speed.

 

You're not expected to be tapping out your four lanes of bandwidth at all times with all of your devices, which is why the Z370 PCH has a whole 24 PCIe lanes afforded to it. The issue with RAID, however, is that both drives are going to be used at the same time, thus you're going to be using twice as much bandwidth. Therefore, RAID's maximum potential can be limited by the DMI link. This isn't even to mention that the DMI link is also used by your Ethernet, USB, and SATA interfaces, too, so if you're downloading something, this can possibly limit bandwidth.

 

Quote

Would it be better then to take the i7 7820X instead of the i7 8700K?

I'm on the fence about which one to take for my new build, the i7 7820X is about the top of what i'm going to spend on a cpu.

The i7 8700K is what i wanted to go with, but if it's going to bottleneck the SSDs than that could be a problem.

Maybe? If you need maximum bandwidth, sure, but I guess I'm not someone who cares way too much about this, so I can't really help you here.

 

You should also be aware of how much you'll be spending on a motherboard, too. Remember that the price of a motherboard and a cooler are part of the price of your CPU.

 

Quote

I currently prefer intel since i'm not so comfortable with AMD cpu's at the moment and I postponed this build long enough maybe on my next build.

 

Thank you very much ^^

Any particular reason why? The i7-7820X gives you only 28 PCIe lanes, while Ryzen 1900X gives you a whole 64 PCIe lanes. In my opinion, I think this may now be worth considering, but this is ultimately your decision.