I have 2 servers
Server A running ESXi 5.0
Server B running ESXi 6.7 U3
On server A I have a 800 GB virtual disk that I want to copy to Server B
Whats the best method
Bother ESXi server on same subnet.
I believe this community post apply to your problem: unknown
In that example, it says to copy VMDK and VMDK-flat files from server A datastore folder to Server B and then attach server B. I think it is the faster option.
VMware converter would be a good way to clone de vDisk but low on performance.
If server A doesn't need the disk any more, your best option would be to dettach the disk from server A and attach it to Server B.