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  1. #29
    New ROGer Array
    Join Date
    Sep 2015

    I have been having the same problems that have been reported by others in this post with the SM951 NVMe 512GB drive (on a Maximus VIII Hero motherboard). First there's the FUA command issue which has to be rectified by checking the “Turn off write-cache buffer” option. More worryingly the drive seems fine immediately after start-up but speeds drop to 40-80 MB/s after a few minutes, and restarting does not fix the problem - only a full shut down does. The Intel drivers helped with the drop in speed but as reported by GTCrais the disk was not be visible to the BIOS when restarting unless after a full shut down. Tinkering with various BIOS and power options has made absolutely no difference to any of these issues.

    However, I then invested in an M.2 to PCIE card (Lycom DT-120 PCIe 3.0 x4 - approx £12 from Scan) so that I could try moving the drive around. Putting it in the PCIE_X4_3 slot made no difference, which is not surprising given that this PCIE slot uses the same lanes as the M.2 slot. However, putting it in the PCIE_X8_2 slot rectified all but the FUA command issue. The drive runs at full speed with no slow down using both the Microsoft and the Intel NVMe drivers, and there's no issue with the drive not being recognised by the BIOS when using the Intel drivers. Both drivers seem to produce similar results on benchmarking (approximately 2700 using AS SSD). I've had it running for 2 days now and all seems well.

    So it appears that connecting the drive using PCIE lanes that communicate directly with the processor allows the drive to function properly with both Microsoft and Intel drivers, whereas connecting it using PCIE lanes that communicate via the PCH causes the problems that I and many others have experienced.

    Obviously there are down sides to moving the drive to the PCIE_X8_2 slot. It effectively means that an SLI setup is not possible, and even with a single graphics card in the PCIE_X16/X8_1 slot it drops to 8 lanes (although I suspect that's unlikely to be an issue for most graphics cards). It also wasn't possible to just move the drive - it required a re-format and Windows to be re-installed.

    I'm not sure if this would work on other motherboards, but it certainly seems to on the Maximus VIII Hero I'm using. Hope this helps others with getting their drive working properly.

    As a bit of an aside, I see that Asus has issued a further BIOS update for this motherboard recently (0902), although it is a beta version. I've tried updating to this version of the BIOS and reinstalled Windows with the drive back in the M.2 slot. Sadly it does not rectify any of the issues with the SM951 NVMe drive with either the Microsoft or Intel NVMe drivers, and actually caused my PC to fail the POST with the Ai Overclock Tuner set to XMP. This was never a problem with BIOS version 0802 so I've rolled it back.

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