GA-Z97X-UD5H-BK with SSD M.2 Plextor M8PeG 256gb. low speed after shut down

[Jozer1]

Hi. I have a problem with GA-Z97X-UD5H-BK (rev.1.0, bios F8) and my SSD Plextor M8PeG m.2 NVME 256 gb (latest firmware, 1.06). SSD is inserted into the PCI-E ASUS adapter (HYPER M.2 X4 MINI CARD), works in the ACHI mode.

When I install windows (win7 x64 or win10 x64) and I hold testing of speed, my ssd works at full speed (2000 mb/sec read, 880 mb/sec write) in any tests (CrystalDiskMark, ATTO Disk Benchmark). I can make soft reset any number of times and speed remains former.

  But when I am shut down my PC, I switch off a supply, then I turn on the computer, and again I hold testing of speed of ssd, it shows low speed in all tests (about 170 mb/sec read, 180 mb/sec write). And further it always shows such low speed, switching off and reset doesn't influence change of speed in any way. SSD works at such low speed.

I tried to use the plug of m.2 port on the motherboard - all in the same way.

Please help to solve a problem! (sorry for my english)

1. MB GA-Z97X-UD5H-BK (1.0), bios F8.
2. RAM - G.Skill F3-2400C10D-16GTX, 2x8Gb.
3. CPU – i7-4790K
4. Video – Gigabyte GeForce GTX 970 G1 Gaming 4096MB
5. SSD - Plextor M8PeG 256Gb M.2 2280 MLC

[shadowsports]

Greetings,
This all comes down to hardware compatibility.  I fully understand your expectation since your are seeing good performance until a cold boot is performed.  But the fact is, this hardware is not supported on your board and looking for an older x2 compatible m.2 drive would not be a wise investment. 

x4 m.2 is not supported with or without the adapter.  You may even be doing yourself an injustice by bringing the performance of your x16 slot down to x8 when the second slot is populated.  My only suggestion is to try another driver, since the one you are working with fails to negotiate or allocate the resources needed to support the hardware.  Not hopeful since 10 yields the same results. 

Issue can be related to any or all of the following:

BIOS rev
BIOS setting(s)
Driver version
Hardware compatibility (drive, chipset on card, etc)

Sorry I don't have something more encouraging.  You can mess with it and might get lucky, but since it doesn't work under 7 or 10, I wouldn't be too hopeful.  Maybe someone else here has some ideas??