My results from a Saumsung 960 Pro NVMe on Pimoroni NVMe Base.
In the UEFI Bios when switching between PCIe modes, the Write speed does seem to scale up.
However even in PCIe 3.0 , the write performance is still about 45% slower it seems than when running native without ESXi
ESXI PCIE 3.0
Category Test Result
HDParm Disk Read 229.82 MB/sec
HDParm Cached Disk Read 218.94 MB/sec
DD Disk Write 274 MB/s
FIO 4k random read 108936 IOPS (435744 KB/s)
FIO 4k random write 42139 IOPS (168559 KB/s)
IOZone 4k read 82396 KB/s
IOZone 4k write 76295 KB/s
IOZone 4k random read 42185 KB/s
IOZone 4k random write 78336 KB/s
Score: 22485
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ESXI PCIE 2.0
Category Test Result
HDParm Disk Read 223.37 MB/sec
HDParm Cached Disk Read 221.80 MB/sec
DD Disk Write 161 MB/s
FIO 4k random read 84628 IOPS (338512 KB/s)
FIO 4k random write 56109 IOPS (224438 KB/s)
IOZone 4k read 86332 KB/s
IOZone 4k write 59302 KB/s
IOZone 4k random read 42104 KB/s
IOZone 4k random write 81483 KB/s
Score: 21933
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ESXI PCIE 1.0
Category Test Result
HDParm Disk Read 195.09 MB/sec
HDParm Cached Disk Read 189.17 MB/sec
DD Disk Write 89.0 MB/s
FIO 4k random read 49112 IOPS (196450 KB/s)
FIO 4k random write 26089 IOPS (104356 KB/s)
IOZone 4k read 69327 KB/s
IOZone 4k write 61822 KB/s
IOZone 4k random read 37869 KB/s
IOZone 4k random write 66519 KB/s
Score: 14962
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Raspbian Native - PCIE 3.0
Category Test Result
HDParm Disk Read 805.45 MB/sec
HDParm Cached Disk Read 768.90 MB/sec
DD Disk Write 425 MB/s
FIO 4k random read 208979 IOPS (835918 KB/s)
FIO 4k random write 93090 IOPS (372363 KB/s)
IOZone 4k read 253909 KB/s
IOZone 4k write 185510 KB/s
IOZone 4k random read 61137 KB/s
IOZone 4k random write 206127 KB/s
Score: 49472