PCI-E explanation

Hey guys
I am a bit confused about the specifications of PCI-E x? slots,and was hoping you could help me.

I am looking to exchange my mainboard and need 2 PCI-e 2.0 x8 slots to run my sas controllers on,and was looking at this mainboard ASRock > Z77 Pro4-M

Now,my retailer has this board specified as having:
1 x PCIe 3.0 x16
1 x PCIe 2.0 x16
1 x PCIe 2.0 x16
1 x PCIe 2.0 x1

Which clearly shows it has the 2 slots i need,HOWEVER on Asrock homepage under specifications for the mainboard they have it listed like this:

- 1 x PCI Express 3.0 x16 slot (PCIE1: x16 mode)
- 2 x PCI Express 2.0 x16 slots (PCIE3: x1 mode; PCIE4: x4 mode)
- 1 x PCI Express 2.0 x1 slot

So,what exactly does that mean (PCIE3: x1 mode; PCIE4: x4 mode)???

Can this board use 2 sas pcie x8 cards at the designated speed?

I was looking at this Supermicro | Products | Motherboards | Xeon® Boards | X9SCL-F but it is 3 times as expensive,as i also have to exchange my ram then.

It would mean that even though they are PCIE X16 physically, two of them are electrically operating in an X4 bandwidth.

As far as I can properly remember, the X16 lane (the one of the op) would be able to run an X8 card. Hell, I've even seen people put in PCIE-1X sound cards in an electrical X16 slot.

Why not purchase two X4 SAS Raid Cards instead of X8?

TheCyberMan said:

With that board you have listed only one of your sas controllers will operate at x8 bandwidth if inserted into the x16 slot.

The max bandwidth your second sas controller will operate at is x4 if inserted into the appropriate slot.

So the answer to your question is no i am afraid.

OK, thank you. However, i have an "old" supermicro saslp-mv8 8port sata controller which i belive is 4x pcie and my new ibm serveraid 1015M is 8x pcie, could i then use both of these,instead of purchasing another ibm card,and have them work at designated speeds?

TheCyberMan said:

You can use your current sas controllers just one of them will work at x4 not x8 as long as put in correct slots will probaly affect transfer speeds somewhat but can still be used.

It is always better to use cards that can operate at the same speed unfortunately the PCIe slots on your board do not allow for two cards to operate at x8 speed so you are going to have a speed mismatch.

Using the old card is going to be the same one card running at x8 in x16 slot and then other working at x4 in x4slot.

If you want to run both cards at x8 then a different mobo that has two PCIe x8 slots or x16 slots will be needed.

I just had an idea, i have 2 other computers and this mainboard ASUS - Bundkort- ASUS M4A785TD-V EVO is in one of them,now i did a little research,and my Supermicro saslp-MV8 runs at pcie 4x and my IBM serveraid 1015M runs at pcie 8x could i simply exchange my current asrock mainboard for my asus one,as the asus seems to have the slots i can use?

TheCyberMan said:

That board supports one PCIe slot running at x16 and one running at x4 so you aren't going to have two slots that can run at x8 speed(bandwidth).

You need a mainboard that has two slots to run at x8 not one slot that runs x16 and the other x4 for them to be both running at same bandwidth.

And, if you'd ever like to add a PCI-E X16 graphics card, a Z77 based board wouldn't have enough PCI-E lanes to get X16, X8, and X8.

An X79 board would supply enough lanes, but that would require a new CPU (Socket 2011), maybe new RAM (X79 supports quad channel, although it's not required), and the graphics card would be mandatory (no graphics in an LGA 2011 CPU). It'd be expensive, but maybe more apropos two SAS controller cards.

I would look for a motherboard a little more balance in the PCI-E 16 lane slots. Most will do 1 at 16 lanes or 2 at 8 lanes. Are you going to be needing a dedicated graphics card too, or is this a server?

For instance, this board supports 2 PCI-e 16 slots running at 8 lanes each and a third at 4x:

http://www.asus.com/Motherboard/P8Z77V_PRO/

TheCyberMan said:

That board supports one PCIe slot running at x16 and one running at x4 so you aren't going to have two slots that can run at x8 speed(bandwidth).

You need a mainboard that has two slots to run at x8 not one slot that runs x16 and the other x4 for them to be both running at same bandwidth.

You guys seem to be missing the point..

I have 2 sas controllers 1 Supermicro requires pcie x4 and 1 IBM 1015 requires pcie 8x, this is a server with ONBOARD gfx,so NO GFX Card would EVER be installed,and it is run headless (when it works).

Reason i asked about 2 x8 slots was because i was gonna buy ANOTHER ibm serveraid 1015M, but if i can get it to work using EXISTING hardware,i wounldt need to spend more money on this,i could just exchange mainboards from my server to my other computer.

Why i made this thread was to understand the pcie lane speeds,and if my 2 current controllers could run on any of my current hardware.

And since x8 cards will work in a x16 slot at 8 speed, and the other one is x4 speed,it should work provided my asus board will accept a non-gfx card in the x16 slot (some mainboards require x16 cards in the x16 slot to work)

Am i correct in my asumption? getting these 2 controllers IBM Redbooks | ServeRAID M1015 SAS/SATA Controller for System x and Super Micro Computer, Inc. - Products | Accessories | Add-on Cards | AOC-SASLP-MV8 to work fine on this board? ASUS - Bundkort- ASUS M4A785TD-V EVO