Question MSI Board M.2 Port Confusion

[Fireflew]

Hi,

Just in the process of building a new PC and have a quick question regarding where to put my M.2 drives.

I have two Samsung 990 Pro 2TB drives and I want to install them on a MSI MPG Z790 Carbon WIFI board.

There are five M.2 slots on the board with the following specs:

M.2_1 Source (From CPU) supports up to PCIe 4.0 x4 , supports 2280/2260 devices
M.2_2 Source (From CPU) supports up to PCIe 5.0 x4 , supports 22110/2280/2260 devices
M.2_3 Source (From Chipset) supports up to PCIe 4.0 x4 , supports 2280/2260 devices
M.2_4 Source (From Chipset) supports up to PCIe 4.0 x4 , supports 2280/2260 devices
M.2_5 Source (From Chipset) supports up to PCIe 4.0 x4 / SATA mode, supports 2280/2260 devices

Here's an image of the board with the slots numbered:

https://imgur.com/6hxK9HH

Originally I was planning to put the two drives in slots 1 and 2 because I was told they would have the best bandwidth being close to the CPU. But then I read elsewhere that putting them in the wrong slots can halve the speed of the GPU (I have a 4090 btw). Do I avoid the top 3 slots and use 4 and 5 instead? I obviously don't want to gimp the GPU in any way!

Any help would be very welcome!

 

[Eximo]

I would use slot one for your OS and then slot 3 or 4 for your other SSD. If I recall the DMI between LGA1700 chips and their chipset is 8x lanes wide, so really two drives on the chipset can easily share nearly maximum bandwidth with no issues. Have three on the chipset is no big deal, you aren't likely to hit all of them at the same time.

You can leave slot two empty to be sure. Some motherboards have a BIOS setting that lets you switch the PCIe 5.0 M.2 slot to PCIe 4.0 mode, but that means the board has a PCIe switch just for that and not all of them will have bothered with the expense.

 

[SkyNetRising]

Do I avoid the top 3 slots and use 4 and 5 instead? I obviously don't want to gimp the GPU in any way!

Usage of slot M2_2 (#2 in your photo) switches graphics card into x8 mode.
Avoid using this slot.
Use all the other slots for your M.2 drives - #1,#3,#4,#5.

 

[Fireflew]

Thanks for the quick replies, very helpful. I'll use slots 3 and 4.