How to get into SCSI without being capped by the PCI bus?

I asked around about the "SCSI Card in the PCIe16x slot and this is what I got"

My Email to Motherboard Editor at Anandtech.com

Good Day Sir,
I am terribly sorry for bothering you, but I have a question. No one from any motherboard, Chipset or product manufacturer would respond to my questions for support. So I turn to you guys over at anandtech. I hope you can help me.
On an NForce 4 SLI Chipset motherboard, you can have up to 20 active PCIe Lanes at one time depending on your configuration. The 2 “Graphics” 16x PCIe Lanes are my question of concern. I have an unusual topic about a PCIe SCSI Raid Card. It is an LSI U320 SCSI Raid Card with a PCIe 8x Interface.

My question is, Can I set the Motherboard to “SLI” mode (Enabling 2 – 8x8 PCIe Slots) Use one For a High End Graphics card and the other for my SCSI card? Or Do I have to use 2 video cards? I know this is not a common question because most people only care about using these slots for video cards. Another reason I ask is because on (for example) the DFI Lan Party SLI-DR motherboard the specs say “ In SLI mode 2 graphics cards can be used in an 8x8 configuration, or single VGA mode will enable 1 PCIe 16x Slot and the other PCIe 16x slot will run at 2x Bandwidth. Well I will only be running one video card. And 2x bandwidth will not be enough for my SCSI Card.



I just want to take all the precautions before I spend 800 USD on this SCSI card. I need to make sure it works. And Unfortunatly, NVidia, DFI, and LSI all were unable to help me, and pointed me to someone else until No one could answer my question.

Thank you for your time, and I appricate your help if you could.


Their Response:

I have asked several manufacturers the same question and gotten some confusing answers. The best I understand at this point is that you CANNOT use anything but a video card in slot 2 of the nForce4 when it is configure 8X/8X. There is some good news, because I have been assured the 8X PCIe SCSI will work fine in slot 2 on the new ATI Crossfire boards.

Wesley Fink​
Senior Editor, AnandTech, Inc.​

 
Hmm, well, that is strange. But I guess we're starting to get a little off topic for this forum. But I've been working very extensively with PCI-E stuff (at the electrical and protocol level) and I can't quite think of any in the protocol to specifically enforce that only graphics cards will work in a particular slot. Maybe I'll have to talk my manager into letting us get an SLI motherboard in the lab and hook up the PCI-E protocol analyzer with a SCSI or SAS RAID controller in the slot and see what happens...
 
UICompE02 said:
Hmm, well, that is strange. But I guess we're starting to get a little off topic for this forum. But I've been working very extensively with PCI-E stuff (at the electrical and protocol level) and I can't quite think of any in the protocol to specifically enforce that only graphics cards will work in a particular slot. Maybe I'll have to talk my manager into letting us get an SLI motherboard in the lab and hook up the PCI-E protocol analyzer with a SCSI or SAS RAID controller in the slot and see what happens...
Click to expand...
If I had the money to test it I would. I plan on buying a PCIe SCSI Raid card with whatever Mobo I get, But I dont want to drop all the money and then have it magically not work, you know. This is a big issue for me, but no one seems to have tried it yet, for whatever reason. Every one just wants faster video cards. :(
 
USMC2Hard4U said:
If I had the money to test it I would. I plan on buying a PCIe SCSI Raid card with whatever Mobo I get, But I dont want to drop all the money and then have it magically not work, you know. This is a big issue for me, but no one seems to have tried it yet, for whatever reason. Every one just wants faster video cards. :(
Click to expand...

Well, I have access to several of the specific PCI-E SCSI RAID card we've been discussing and a PCI-E protocol analyzer. However, since our lab is focused on testing with server and high-end workstations, we don't have any SLI capable motherboards sitting around. I'll see if I can find one laying around the building somewhere and give it a try when I have a spare moment.
 
Actually, now that I think about it, I have tested with one of these guys: http://www.hp.com/workstations/pws/xw9300/

It's an nVidia/AMD thing with dual x16 SLI slots. I was able to use my PCI-E x8 cards in either or both slots without a problem. I don't know how this chipset is different from a standard nForce4, however. Though, they are based on the same design.
 
The feature set of the NF4 SLI and NF Pro is nearly identical - 20 PCI-E lanes, 10USB ports, 4 SATA-II ports, GbE w/ TCP offload&SNE. Given the nearly identical feature set and interconnect, I'd expect they are much the same silicon. However, I would not be suprised if NV has modified some traces on the NF4 SLI to deliberately limit the functionality of the PCI-E slots to graphics cards, much like SLI is disabled in the NF4 Ultra despite it being the same silicon as the NF4 SLI. I also doubt you'll get a straight answer on this from Nvidia.
 
DougLite said:
The feature set of the NF4 SLI and NF Pro is nearly identical - 20 PCI-E lanes, 10USB ports, 4 SATA-II ports, GbE w/ TCP offload&SNE. Given the nearly identical feature set and interconnect, I'd expect they are much the same silicon. However, I would not be suprised if NV has modified some traces on the NF4 SLI to deliberately limit the functionality of the PCI-E slots to graphics cards, much like SLI is disabled in the NF4 Ultra despite it being the same silicon as the NF4 SLI. I also doubt you'll get a straight answer on this from Nvidia.
Click to expand...
Well This is what I got from all the companies... and why I wrote the email.

LSI : The Card should work in any PCIe 16x or 8x PCIe slot. But Contact your Motherboard Company for confirmation.

DFI : The way the traces are set up for the 2 PCIe 16x slots to work at the same time (SLI mode) is only if they are both using graphics cards, because the data in the lower PCIe16x slot is being forwarded up to meet with the data in the first slot, so it can appear as one data stream to the chipset. However it may work, you should contact NVidia for confirmation.

NVidia : You have to contact the SCSI card manufacturer and the Motherboard maker for confirmation...

So it got me no where :( The only thing that really makes sence is what DFI is saying.
 
You know, I was just on Wednesday visiting with some nVidia engineers at a PCI-SIG event... If I had known about this question at the time I could have asked them. I'll see if I have their contact information back at the office and pretend it's a work-related question :)
 
Just wanted to add some info. I'm 99% sure the K8WE is unique in that the PCI-E 16X slots are not just for video cards, but what ever you want. If you have 2 CPUs installed you could run a video card in one slot and a RAID card in the other without problems.

If you do not want dual processors or ECC registered RAM but you do want a high end RAID card ( PCI-X ) this is the only option I am aware of :

DFI 855GME-MGF
 
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