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PCIe ports/M.2 port lanes usage

White_Wind
Level 7
Hi I'm opening this thread to catch a bit more attention on my question, since the answer will make me buy a Z97 ASUS board or no board at all.

It may be a bit too early to be able to answer it, but I wonder if I could plan to use two M.2 PCIe 2.0 x2 SSD's set in Raid0.. one in the PCIe 2.0 x4 port ( through an adapter ) and the second one in the M.2 x2 port.

Now on the Gene/Hero product pages, here's what to be read : "The PCIe 2.0 x4 slot (PCIEX4_1) shares bandwith with mPCIe 2.0 x1 and M.2 slots. The default setting is in Auto mode that automatically optimizes the system bandwidth. If you install PCIe 2.0 x4 device, the system will automatically detect and disable mPCIe 2.0 x1 and M.2 slots."

So it mentions a "PCIe 2.0 x4 device", but what about PCIe 2.0 x2 devices ? I would have thought that since the two ports share bandwith, pluging a x2 device in the PCIe x4 port would allow for two lanes to be still available in the M.2 port...no?

Also what is that default Auto mode... would there be a manual mode to configure lane availability amongst ports ? THAT would be the sweetest thing

And if both ports were able to operate simultaneously at x2 speed each, by any means...would SLI x8 x8 still be available on the 3.0 ports ?
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14 REPLIES 14

Praz
Level 13
White Wind wrote:
It may be a bit too early to be able to answer it, but I wonder if I could plan to use two M.2 PCIe 2.0 x2 SSD's set in Raid0.. one in the PCIe 2.0 x4 port ( through an adapter ) and the second one in the M.2 x2 port.

Hello

RAID has never been possible at the motherboard level using PCIe devices. Z97 bring nothing that changes this.

White_Wind
Level 7
Oww, right yeah... thank you

Now will check what can be the prices of PCIe 2.0 x4 ----> M.2 x2 SSDs Raid cards..... darn, if such things exist x)

IM2L844
Level 12
Maybe this will answer some of your questions:

http://techreport.com/review/26443/this-is-intel-9-series-chipset

I think I'm going to wait on the 100 series chipset and give this stuff a little more time to develop. We'll see.

White_Wind
Level 7
Thanks for the link, good read.

Yeah I think I'll do the same as you, but still nice to have a M.2 slot, and also that Asus made it x2.

White_Wind
Level 7
Sorry to double-post, I just wanted to add that the PCIe 2.0 x4 port can operate :

at x4 : M.2 and x1 ports will be disabled

at x2 : this mode is called M.2 mode. The M.2 port will still be available at x2, and x1 ports will be disabled

at x1 : no more info

Hrafn
Level 7
White Wind wrote:
It may be a bit too early to be able to answer it, but I wonder if I could plan to use two M.2 PCIe 2.0 x2 SSD's set in Raid0.. one in the PCIe 2.0 x4 port ( through an adapter ) and the second one in the M.2 x2 port.

I think you'd be better off using a 4-lane PCIe M2 (such as the Samsung XP941). In order to fully utilise this you'd need either a 4-lane M.2 port (AFAIK, only Asrock does this as yet, marketed as "M.2 Ultra"), or a PCIe x4 to M2 adapter card that actually passes all 4 lanes onto the M.2 (such as the upcoming ASUS Hyper M.2 X4 adapter).

Hrafn wrote:
I think you'd be better off using a 4-lane PCIe M2 (such as the Samsung XP941). In order to fully utilise this you'd need either a 4-lane M.2 port (AFAIK, only Asrock does this as yet, marketed as "M.2 Ultra"), or a PCIe x4 to M2 adapter card that actually passes all 4 lanes onto the M.2 (such as the upcoming ASUS Hyper M.2 X4 adapter).


I totally agree, but at the moment I have a m-atx setup! I made the mistake of jumping to quick, without reading the M2 limitations correctly, I assumed x 4 only to find out, it x1 or x2. And being m-atx, if you run dual sli cards, you don't have another slot.
486 Dx2 running dos 6.2 and Windows 3.1

Grumpy OLD git wrote:
I totally agree, but at the moment I have a m-atx setup! I made the mistake of jumping to quick, without reading the M2 limitations correctly, I assumed x 4 only to find out, it x1 or x2. And being m-atx, if you run dual sli cards, you don't have another slot.

Yeh, I've been looking at M.2 implementations on the latest round of mATX MBs, and it does strike me as generally half-arsed. A fair number don't have M.2 at all, and almost all that do have it sharing a couple of PCIe lanes with a couple of the Intel SATA ports (the VII Gene is the one exception). It would make far more sense for M.2 to share all four lanes of the (commonly implemented) PCIe x4 in the last mATX slot position anyway. (i) As you point out, this slot is unusable to anybody running dual SLI, so these lanes will be frequently idle. (ii) Although almost nobody is producing M.2 x4 cards yet, the best way to encourage them to do so is to produce MBs actually capable of using them.

Grumpy_OLD_git
Level 7
I run a plextor 256 m6e m.2 SSD, and in hind site , I would say I jumped to fast, yes it's nice and small, and a wee bit faster, but the z97 board is not great, in time I think we will see dual m.2 ports, running x4 lanes, then m2 will be worth it, for now, my advice is stay away from them, also there major compatibility issues, as example crucial m.2 does not work in Asus boards.

Playing with M2 cost me nearly £460, and the result are totally not worth it. Just like the new z97 board, I would say wait.
486 Dx2 running dos 6.2 and Windows 3.1