My buddy Alan Renouf had pinged me earlier today and asked whether it was possible to emulate a USB storage device that could aide him in the testing the installation of ESXi from a USB device but without having to use a real USB device. I honestly was not aware of any mechanisms that would allow for this and I normally would just passthrough a real USB device to a Nested ESXi VM for this type of testing purposes.
While thinking about his question, I also recall we had made some enhancements to our Virtual USB interface that would allow user to back it using a disk file. While searching further, I came to learn that not only was this possible, but it was also a common method for testing USB-based installation without the hassle of messing with physical hardware. It turns out you can just present a Virtual Disk (VMDK) to a VM running ESXi (Nested ESXi) and through a special driver, it will recognize the device as a USB storage device!
I definitely wish I had learned about this earlier and it goes to show, all the hard engineering efforts made by our VMware Engineers to make testing and using our software as easy as possible even without needing real physical hardware 😀