I guess it's not the disk itself that may be a performance bottleneck when multiple VMs will perform intensive disk operations simultaneously. It's the disk controller (or host adapter, to be precise).
If you have multiple disks on a single controller, it will impact performance in a similar way as if it were a single disk. It will be better than single disk,...
Don't use dd as a tool for measuring performance. The command line arguments given to dd in your example allow the host OS to cache the writes in RAM. So the results here are likely skewed by the amount of RAM available for caching in the host OS vs the guest OS. fio is a much more relevant tool for benchmarking.
GPT Disk and Non-Linux:
virsh shutdown myVM
qemu-img info mydisk.img
sudo qemu-img resize mydisk.img 50G
sudo sgdisk -e mydisk.img
New size of mydisk.img of myVM will be 50G and gpt partition table backup will be re-taken to the last sectors of disk. Otherwise most OS does not recognize disk as resized ... Linux does because gparted automatically fixes ...
It is now possible to import Hyper-V VMs directly without having to convert them first. There are two main paths: importing the VM like you would an OVA (this guide uses PowerShell), and Using AWS Systems Manager for Microsoft SCVMM.
In case anybody stumbles upon this: the solution to such a problem is to set rombar=0 in the PCI passthrough in your vm.conf:
(whereas 06:00.0 is the relevant slot you want to passthrough)
Qemu is a processor emulating virtualization software with many virtual devices support such as hdd,mb,ram,snd,eth,usb,vga... KVM is a kernel module which allows passing through cpu cores via host-passthrough without virtualizing them. It also allows passing through pci devices via vfio-pci kernel module. All these are possible via IOMMU (Input output memory ...