Showing results for 
Search instead for 
Did you mean: 

Samsung 950 Pro M.2 and BCLK on XMP profiles causing downgraded M.2 speeds

Level 7
So I am looking at building a new computer to replace my 10 year old piece of junk. I was reading about the Samsung 950 Pro M.2 and stumbled upon this article. I am bringing it here to help those that might be having a similar issue:

The issue we had is worth drawing attention to since no faulty components were involved. We use an X99 motherboard for SSD testing, specifically the Asus Rampage V Extreme. However, when we originally tested the SSD 950 Pro drives both were being capped in performance. A later installation of a beta version of the Samsung Magician software revealed that the PCI-E link speed was being limited to 5Gbps, i.e. PCI-E Gen 2.0 instead of Gen 3.0, which the drives need to operate at full speed.

The problem turned out to be something as simple as our overclock settings. We use Corsair Vengeance LPX DDR4 modules rated at 2,800MHz, and we were using their built in XMP profile for our system's overclock. However, this automatically sets the base clock to 125MHz, which is a requirement when using high frequency memory (i.e. above 2,666MHz) on X99. However, this also affects the speed of other parts of the CPU, not just the cores, and one of those parts is the onboard PCI-E Gen 3.0 controller. In turn, in order to maintain PCI-E stability at this clock, our motherboard was downgrading the PCI-E interfaces to Gen 2.0. You can force the graphics slots back to Gen 3.0, but there's no such option for the M.2 slot, which makes sense since storage devices require perfect stability. We have not been able to confirm exactly how other motherboard manufacturers handle the situation, but it's probably safest to stick to 2,666MHz DDR4 on X99 when using a PCI-E 3.0 storage device. It should also not be a problem on Z170, where the PCI-E controller's clock is separate to the CPU BCLK.

The article downclocked their DDR4 to 2666MHz and reset their BCLK to 100 which allowed them to complete the benchmarks. I have also read on some older references that the point in which the BCLK gets pushed to 125 is anything above XMP 2400MHz, so I dont know which one it is: 2400 or 2666? Can anyone confirm?

I am in the process of acquiring all parts for my build and was going to go with 2400Mhz G.Skill DDR4 to be on the safe side since I want to use the 950 Pro as my main drive, and I'm not an experienced overclocker so stability and simplicity is my main concern.

I know Chino recommended as an alternative to use a PCIe adapter card, but my question is, would there be any performance loss with this method?