Hi all,

 

I apologise for the similarity of this question to other threads, but i have only managed to find information on the inter-compatability of PCIe slot sizes and no definitive answers to transfer rates.

 

I have an Asus P5QPL-AM mobo in my unraid DIY build and am, at the moment, using a PCI 4 channel raid controller, but am looking to switch to PCIe and make use of both the x1 and x16 (GPU) slots on the board.

 

I have googled the topic and am aware that i can use the x1 slot with a two channel controller with no significant performance sacrifices, but am not so sure about the x16?

 

My mobo manual says that the x16 slot is for a GPU, but more googling has revealed that others have plugged a x1 raid controller in the slot with no trouble, so there is no worry of slot size compatibility.

 

Where i get confused though, is re transfer rates. My natural assumption is that if a x16 slot can also house x1 - x16 cards it would also be able to automatically switch to the relevant transfer speed, but even more googling (extreme noob with PCIe) has informed me of such things as 'x1 mode' which a post in another forum suggests the intel chipset on my mobo has. Meaning that if I plug anything less that a x16 card into the x16 slot, it will work, but clocked down to a reduced x1 speed, which as i am looking at buying a four channel card, would put me over the recommended two channels, for a x1 slot.

 

So my issue is this... As my x16 PCIe slot will take smaller slot sizes, i would like to install the recommended

'Adaptec 2241000-R PCIe x4, 4 channel (3.0Gb/s) (1430SA SGL)' controller,

but if the chipset on my mobo is going to clock back the transfer rate to x1 (as it is not a x16 card) i would be better off just buying two, 2 channel PCIe x1 controllers, one each for the x1 and x16 slots, as not to compromise transfer speeds.

 

I'd appreciate some advice, as i am very new to PCIe and quite clearly don't fully understand the whole 'interconectivity of slots' thing, lol.

Does my scenario hold water, or have i just written down a load of rubbish and will be fine plugging a PCIe x4 four channel card into the x16 slot, with no sacrifice in performance?

 

Thank you (very much) in advance,

 

Rich  

PCI-e will run the board as fast and as many channels as the bus can take upto the max available to the chipset. So your adaptec x4 card will run at x4 in a x16 slot. It's a good sign the x1 card works, but still isnt proof the x4 will work.

 

Ideally for future expansion reasons you want as many ports as possible in your x16 slot. Typically you'd look at a 8 port sata card in such a slot. However if you dont plan on going above 10 or 12 disks (4 onboard, 4 on PCIx16, 2 on PCI-e x1, 2 on PCI) then 4 port pci-e card makes sense. 

 

As for speed each x1 in PCI-e is worth 250MB/s (in PCI-e v2.0 it is doubled). An 8 port sata card with x4 PCI-e can theoretically still deliver 125MB/s which is more than todays HDDs can sustain. 

 

Even a pair of cheap x1 2 port sata cards will be a significant improvement over the 4 port PCI card when it comes to partiy checks. If your system will only ever hold 8 disks then this is the cheapest and best option IMO.

Thanks for the quick reply, most appreciated.

 

I have managed to find some more information scattered around (however no definite yes or no), which again makes it look like the Intel G41 chipset, might actually limit the slot to PCIe x1 when a non PCIe x16 / GPU card is being used!? I appreciate that your (probably) not a specialist on Intel chipsets, but is that something that you've heard of, or is likely to happen?

 

Rich

You should not have a problem according to this: http://www.tomshardware.co.uk/forum/265741-12-intel-chipset-limitation-video-post-pcie-slot

 

Anything greater the PCIex1 will disable digital video but VGA will still work.

Thank you, i have actually already looked at that thread

 

But my concern is not with digital/vga output, it is weather the PCIe x16 slot will be limited to x1 if i put a PCIe x4 raid controller in it, something the Intel G41 chipset apparently may do?

The thread says that it will work.

Cool, I just wanted a second opinion, as I've read a few other bits that say otherwise.

 

Fingers crossed then, i'll post back with a defo answer once my card arrives 

Well i am happy to report that the card does indeed work and that my parity check has increased by 35,000-50,000KBps, which is excellent and i'm assuming a good sign that the card is not being limited to PCIe x1?

 

I am also using the Supermicro AOC-SASLP-MV8 8x SATA Controller, instead of the Adaptec 2241000-R x4 channel controller (from the recomemdation above) and its obviously working, as yet, with no problems 

 

So thank you for the advice guys,

 

Rich

 

 

 

Well i am happy to report that the card does indeed work and that my parity check has increased by 35,000-50,000KBps, which is excellent and i'm assuming a good sign that the card is not being limited to PCIe x1?

 

That, does indeed, sound good.  See this thread for information on how to check the actual bus width being used.

 

Are you in a position to prove whether or not the digital video outputs are being disabled?

Sorry, I am very new to unRAID and Linux.

 

What does "lspci -vv" mean and what should I be doing? Major noob, lol.

 

Rich

What does "lspci -vv" mean and what should I be doing? Major noob, lol.

 

"lspci -vv" is a command you type at a console, or telnet, prompt.

I was hoping it was that. I did actually try doing that, via telnet using terminal on OSX but I just get 'command not found'.

Could it be an unRIAD 5 function that i don't have (running 4.7) Any ideas?

Figured it out, had to install the pciutils package, lol.

 

Well i can 100% confirm that the G41 chipset is not limiting the PCIe x16 port below x4, which is what i was hoping for (x4 minimum).

 

LnkCap: Port #2, Speed 2.5GT/s, Width x16, ASPM L0s, Latency L0 <256ns, L1 <4us ClockPM- Suprise- LLActRep- BwNot+
LnkSta: Speed 2.5GT/s, Width x4, TrErr- Train- SlotClk+ DLActive- BWMgmt+ ABWMgmt-