Hi,
You can use the this guide for Hyper-V Server.
You can face slow write performance with RAID 5, that is one of the drawbacks of RAID 5 on the spindle disks. Please find the recommendations.

Thank you for sharing your results and findings.

Thank you for the logs. Do you have folder c:\starwind ? *** VtlPlugin::sscControlRequest: VTL: Copy of Header pattern 'C:\Program Files\StarWind Software\StarWind\VTL\HP_MSL8096_LTO8.vtlp' to 'C:\starwind\vtl1.swdsk' failed (err 3)! Do you have folder c: \starwind? Because error 3 is a path not fou...

I'll try to connect another iSCSI disk to a Vmware host and run some tests with a VM on Esxi, maybe it is not a Hyper-V issue.

Please share your findings.

Hi pmaa,
We got around 30 Gb/s during our internal testing of vmxnet3 adapters using Iperf.

Hi AllanB,
Could you please collect and share the logs?
Please use this tool for logs collection.

Hi batiati,
Please try with fixed .vhdx. Please also make sure that you are using SCSI controller for .vhdx connection.
Did you try proposed tweaks?

You can upload the logs to any filesharing resource and share the link with us.

Thank you for the details. Performance inside VMs can be related to NICs settings on the management network. VMQ should be disabled on all levels, inside VMs as well. Also, EEE control policies should be changed to High performance as well. These changes can be done in Advanced network card settings...

Quite hard to understand the result you want to get.
Could you please provide network diagram?

Please use the version for Windows 2012R2 / Windows 2016.

Thank you for your update

Hi batiati,
Could you please clarify what network cards are you using, what vendor?

Thank you!

You can use StarWind this tool for logs collection.