moved to slot 4, problem solved, thank you, but still cant understand why it worked on slot 2 16x before, and now have to work on slot 3/4?
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I've moved it to slot 4, problem solved, thank you so much, but still don't know why it doesn't work on 16x anymore?
The SSD is PCIe 3.0 x4, put it in a x16 slot won't help anything.
However, due to the cMP firmware issue, most PCIe 3.0 device cannot properly negotiate at PCIe 2.0 speed in slot 1 and 2. Resulting further fall back to PCIe 1.0 link speed. Which means your SSD fall back to PCIe 1.0 x4, theoretical max speed is 1000MB/s, real world max at ~750MB/s.
This issue, however, can be fixed by put a PCIe switch inside the connection. e.g. If you use the Highpoint 7101A adaptor, due to the onboard PCIe switch, the SSD can actually negotiate at correctly link speed.
To avoid this issue, you can install the SSD in slot 3 or 4. Due to slot 3 and 4 share use the same PCIe 2.0 x4 lane. Therefore, there is a build in PCIe switch, which helps the SSD to negotiate at the correct link speed.
To permanently fix the issue, you can upgrade the cMP firmware to 138.0.0.0.0. At this moment, this version may be considered as a "beta" firmware due to only available at the 10.14 beta installer. But this should become formal soon.
