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Asus Z77 line motherboards and PCI-E limitations

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November 29, 2012 3:26:58 PM

I have an IBM ServeRAID M5014 RAID card, it uses PCI-E 2.0 x8. Although I am only going to be using four SATA HDDs in it in RAID5, so it will not be operating at anywhere near capacity.

I am planning to put it in a gaming rig which I am still finalizing the hardware on although I have decided to go with an i7 3770K CPU. So far my motherboard choices are between the ASUS Sabertooth Z77 and ASUS P8Z77-V Deluxe based on the OCT 2012 motherboard review on this site.

The main reason I am also considering the deluxe is because that is a server-class RAID card (Even though its a re-branded LSI) and is somewhat picky about what desktop motherboards it will work in (Namely, it's only officially supported in for IBM servers). I know that it will work on nearly any P8Z77 line ASUS board, but although the Sabertooth is a Z77 board, I don't know if it counts as a P8 line model. (Personally, I like the Sabretooth more than the Deluxe, not to mention its much cheaper.)

On top of that, since this will be a gaming rig, I am a bit worried about the fact that I am going to be forced to either make the RAID or 3D card operate at below it's specs. Both motherboards have two PCI-E 3.0 x16 ports, but they only operate at x8 if both are used at once. Not a problem for the RAID card, but this would make my 3D card suffer (although I have no idea by how much, I am still researching which 3D card to choose, it will likely be a GTX model though).

The Deluxe however has an additional PCI-e 2.0 x4 port, which would let me use the 3D card at a full x16 lanes but then my RAID card suffers at x4 lanes instead of x8. And although as I said before I am not operating it at anywhere near capacity (its meant to work with up to 32 SAS drives, and I am only using it with a SAS to SATA breakout cable for four) I am worried that I am already basically jury-rigging a server card to work on a motherboard its not supposed to, and that putting it on a x4 slot instead of x8 is asking for trouble.

I know this is a pretty unorthodox question, but does anyone have any advice?
a c 121 V Motherboard
November 29, 2012 5:53:04 PM

Well... There is a lot that can be said.

First off, is an easy answer that could make your choice easier.

There are no graphics cards out there (including dual GPU behemoths like the GTX690) that get even close to saturating even 8 lanes of PCIe 3.0 bandwidth.

That means, that if you went with the sabertooth and it dropped the GPU down to 8 lanes, there would be absolutely no performance hit vs running at a full 16 lanes.

Your other part of the question is trickier, since I don't know for sure if the RAID card will be compatible with that specific MB. However, since it is compatible with the P8 line, I would assume it would be.
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November 29, 2012 6:13:41 PM

I was also thinking, any idea if that card would operate fine (or if it would even operate at ALL) on x4 instead of x8?

Because with that extra PCI-e 2.0 slot on the Deluxe, that leaves a PCI-E 3.0 slot open for any future SLI/Crossfire setups. Even though ATM I am just going to go with a single card, i'd like to have that upgrade option later down the road.

The purpose of the RAID5 is for redundancy and fault tolerance (Yes I know, RAID is not backup), not performance. That being said though, I went with that card at the suggestion of a friend because if I am going to drop four 3TB drives in there, i'd prefer the rebuild to take hours, not weeks.
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a c 121 V Motherboard
November 29, 2012 6:35:30 PM

Yes, more than likely the RAID card will run in the x4 slot, and you will see very little (if any at all) performance hit (4 drives x ~120MB/s = ~500MB/s throughput. PCIe 2.0 x 4 lanes = ~1000MB/s bandwidth)

The extra PCIe slot is definitely nice for multigpu.

The other option would be getting a board with a PLX PCIe chip that will effectively double your PCIe lanes (giving you 32).

The board I know of off hand is the Asus Maximus V Extreme, which btw also bypasses the PLX chip when only 1 gpu is used, to cut out any latency added by the PLX chip. (.5-2%)
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November 29, 2012 6:41:31 PM

Thanks for the advice.

As for that board, wow, that is a very nice one... but way out of my pricerange I'm afraid. The other parts in this build are already excessive enough...
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a c 121 V Motherboard
November 29, 2012 8:15:27 PM

No problem :) 
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November 29, 2012 8:22:33 PM

Best answer selected by Cyber_Akuma.
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