The idea sounds so good: Instead of installing your virtual lab on your local hard disk put it on a USB 3.0 stick and have it always in your pocket with you. I wanted to try that and bought a 256 GB USB stick with “sensational read/write speed values” (read speed of more than 350 MB/s, write speed of more than 200 MB/s). When copying the installation sources to the stick the promised value was actually reached. The disappointment started when I ran the first setup of an operating system in Hyper-V: The installation took hours. I tried the same from my local SSD and it was done in less than 10 minutes. What was wrong? Was there a USB driver issue? I was puzzled.
Finally, I found an article in a computer magazine (thank you, c’t) that explained the behavior (https://www.testbericht.de/de/vergleich/ct-magazin-3706.html): When copying big files, the write speed is brilliant and the measured speed even exceeds the vendor specification. However, random read/write operations or copying small files bring it down to 100 kByte/s. This seems to be a general problem of this category of sticks.
Btw, external SDD drives don’t seem to have the issue and are for that reason a much better choice.