MSI B450 Gaming Pro Carbon AC m.2 socket question

[elvasked]

Hopefully someone can help me understand this. I'm putting together a new build.

This MB has 2 x m.2 slots type m.

I'm considering installing 2 x m.2 SSD's on this MB.

I'll be using a Ryzen 7 2700 CPU and will not overclock.

Would like to install like this.

M2_1 with a Samsung 970 EVO ( nVME )
http://

M2_2 with a Samsung 860 EVO ( Sata III )
http://


I understand the section that describes that m.2_1 disables Sata 5 & 6 ports
I understand the section that describes that m.2_2 disables PCI_E2, PCI_E3, PCI_E4 and PCI_E5

That's fine as I won't be using those.

For the second SSD I could buy a 2.5 inch EVO 860 but I'm trying to learn.

860 EVO m.2 and 2.5 inch cost the same and I wouldn't need 2 cables with the m.2.


m.2_1 can use PCIe 3.0 x 4 or x 2 and Sata III ( will put the 970 EVO there as boot drive )
m.2_2 can use PCIe 2.0 x 4 ( would like to use the 860 EVO there as storage )

But as you can see for the m.2_2 slot they only list PCIe 2.0 x 4.......and not Sata III

Since PCIe 2.0 x 4 is about 3 times faster than Sata III does this mean a Sata III drive (860 EVO) will work in that socket ( at Sata III speeds )

or not.

This info is copied from the MSI B450 Gaming Pro Carbon AC manual page 17.

http://


AMD ® B450 Chipset
4x SATA 6Gb/s ports
1x M.2 slot (M2_2, Key M)*
Supports PCIe 2.0 x4 2242/ 2260 /2280 storage devices
AMD ® CPU

1x M.2 slot (M2_1, Key M)**
Supports PCIe 3.0 x4 (AMD ® Ryzen 1st and 2nd
Generation/ RyzenTM with RadeonTM Vega Graphics) or
PCIe 3.0 x2 (AMD ® AthlonTM with RadeonTM Vega Graphics)
and SATA 6Gb/s
Supports 2242/ 2260 /2280/ 22110 storage devices
2x SATA 6Gb/s ports**

* PCI_E2, PCI_E3, PCI_E4 and PCI_E5 slots will be unavailable when installing
M.2 PCIe SSD in M2_2 slot.
** SATA5 and SATA6 ports will be unavailable when installing a M.2 device in
M2_1 slot.

 

[USAFRet]

----------------------------
m.2_1 can use PCIe 3.0 x 4 or x 2 and Sata III ( will put the 970 EVO there as boot drive )
m.2_2 can use PCIe 2.0 x 4 ( would like to use the 860 EVO there as storage )
----------------------------

You have to do them the other way around.

The 970 will work in either port, the 860 EVO (SATA) will not work in the m.2_2 port.

 

[elvasked]

m.2_1 can use PCIe 3.0 x 4 or x 2 and Sata III ( will put the 970 EVO there as boot drive )
m.2_2 can use PCIe 2.0 x 4 ( would like to use the 860 EVO there as storage )
----------------------------

You have to do them the other way around.

The 970 will work in either port, the 860 EVO (SATA) will not work in the m.2_2 port.

................................................................

Would the PCIe 2.0 x 4 reduce the speed of the nVME drive ?

I'd like both drives to work at optimum speeds and I thought the 970 EVO nVME drive needed the PCIe 3.0 x 4 slot.

Again, I do not know this, I just assume it to be the case that PCIe 2.0 x 4 is rated at 2 GB/s and the nVME can be up to 3.5 GB/s.

 

[USAFRet]

Yes.
For full performance of the 970, you have to use the m.2_1 slot.
This also negates use of the 860 EVO m.2.

Maybe just get a regular 2.5" 860 EVO. Same price, same performance, and you're not crippling the 970.

 

[elvasked]

Yes that what I'm going to do.

m.2_1 PCIe 3.0 x 4 for the 970 EVO
M.2_2 PCIe 2.0 x 4 I'll leave empty

2.5 inch 860 EVO in a Sata port.


That's too bad but it's how the MB is designed.

I wonder why they did it that way.

Thank you for the clarification.

 

[USAFRet]

That's too bad but it's how the MB is designed.

I wonder why they did it that way.

Thank you for the clarification.

Because we're in a transition period. NVMe drives (and m.2) are still pretty "new". People wanting 2 of them on the same board, rare.

Just like a few short years ago, having both SATA III and SATA II ports on a motherboard was common, so you had to be mindful of where you connected that shiny new SSD.
Why didn't they just make them all SATA III? $$$ is why.