Asus Z490-E and puzzling M2/Sata slots mess

[HRose]

The image is reference from the manual (updated the image to show the text that was omitted).

 

What I understand is that, on a typical configuration, the videocard takes x16, and putting the M2 on the second slot at the bottom of the motherboard gives that M2 x4, but disables two sata ports, leaving four total still working.

 

What I do NOT understand is what happens if I move the M2 from the second to the first slot.

 

The manual says that ONE sata port is disabled, if the M2 runs in SATA mode. I want it running in x4. Is this possible, or running x4 on the first slot FORCES the videocard to fall back to 8x?

 

Is the first M2 slot only EITHER usable in sata, OR x4 but also gimping the videocard slot?

 

So, with a default of a videocard at 16x, should basically the first M2 slot better being AVOIDED?

 

 

 

 

[Grabhanem]

The main two PCIe slots are running off the CPU lanes, while the M.2 and SATA are running off chipset lanes. They won't affect each other. Two of M.2_2's lanes share bandwidth with SATA ports, and M.2_1's embedded SATA port shares bandwidth with SATA_2.

 

I understand this is worded kinda badly, so in answer to your questions:

 

The manual says that ONE sata port is disabled, if the M2 runs in SATA mode. I want it running in x4. Is this possible, or running x4 on the first slot FORCES the videocard to fall back to 8x? Yes. 4x on either M.2 doesn't affect PCIe1.

 

Is the first M2 slot only EITHER usable in sata, OR x4 but also gimping the videocard slot? It can be used on either and only gimps SATA ports on SATA mode and nothing else.

 

So, with a default of a videocard at 16x, should basically the first M2 slot better being AVOIDED? No, it's better to use honestly since it shares with less other ports.

[HRose]

8 minutes ago, Grabhanem said:

The main two PCIe slots are running off the CPU lanes, while the M.2 and SATA are running off chipset lanes. They won't affect each other. Two of M.2_2's lanes share bandwidth with SATA ports, and M.2_1's embedded SATA port shares bandwidth with SATA_2.

 

I understand this is worded kinda badly, so in answer to your questions:

 

The manual says that ONE sata port is disabled, if the M2 runs in SATA mode. I want it running in x4. Is this possible, or running x4 on the first slot FORCES the videocard to fall back to 8x? Yes. 4x on either M.2 doesn't affect PCIe1.

 

Is the first M2 slot only EITHER usable in sata, OR x4 but also gimping the videocard slot? It can be used on either and only gimps SATA ports on SATA mode and nothing else.

 

So, with a default of a videocard at 16x, should basically the first M2 slot better being AVOIDED? No, it's better to use honestly since it shares with less other ports.

You again

 

So, the manual means the 1/2 columns can be mixed at will?

 

That means I can have a videocard at x16, the second M2 slot at 4x (disabling 2 sata ports), and the first M2 slot also at 4x (without disabling anything).

 

Or:

both M2 at 4x, but losing 2 SATA

one M2 at 4x, one M2 at 2x, all SATA on

 

Is this correct?

 

If I use the first slot, x4, all sata ports still on. Is bandwidth still shared with whatever is connected in Sata 2?

So I guess I should still avoid using the 2nd sata port, for performance, unless I run out of slots?

[Grabhanem]

1 minute ago, HRose said:

You again

 

So, the manual means the 1/2 columns can be mixed at will?

 

That means I can have a videocard at x16, the second M2 slot at 4x (disabling 2 sata ports), and the first M2 slot also at 4x (without disabling anything).

 

Or:

both M2 at 4x, but losing 2 SATA

one M2 at 4x, one M2 at 2x, all SATA on

 

Is this correct?

 

If I use the first slot, x4, all sata ports still on. Is bandwidth still shared with whatever is connected in Sata 2?

So I guess I should still avoid using the 2nd sata port, for performance, unless I run out of slots?

Oh hey, didn't realize it was the same OP!

 

Yep, if I understand correctly, all 3 combinations draw from separate resource pools, so you can mix and match as you please within those restrictions.

[HRose]

I still have doubts because the original image omitted some text at the bottom.

 

The description says that when the second slot is populated then sata 5/6 are disabled. It should be worded more precisely to say that the sata ports are disabled only if the second slot runs at 4x, not "is populated".

 

So I wonder if those lanes are split and not independent...

-

[HRose]

Answering myself: looking at other models' manuals, the configuration 1/2 can be mixed.

 

That means the first slot doesn't share bandwidth and won't remove SATA2, as long it runs in pci-express x4.

 

Both slots can go at x4, but disabling two sata ports.

 

Both M2 and all 6 satas are possible, but the second M2 goes only 2x, and it shares bandwidth with two sata ports.

 

This in theory. While looking into this I found mentions of various problems, like pci-express slots going slower if sata ports are disabled, or M2 slots stuck in 2x. So the implementation might not be flawless, beyond the theory.