Old Fujitsu TX200 S5 (m/b D2709).
What could be the problem?
Very low speed of loading of ESXi (5.1, 5.5, 6.5) (Fujitsu customization) from USB-flash from all USB ports (2.0).
Сhecked on usb-flash 2.0 (Samsung, JetFlash 510S), 3.0 (Transcend).
When loading ESXi, downloading files lasts ~8-9 minutes, initializing ESXi ~60-80 seconds.
If you load any OS with dvd-rom, then the files on the flash drive are read ~ 20 MB/s, the record is ~ 9 MB/s.
With the same usb-flash on the other PC, the ESXi files are loaded in ~20-30 seconds, the initialization is ~60-80 seconds.
(sorry for my English - google translate)
P.S. Tested the USB flash drive in the VM - the speed of writing / reading ~ 4-5 MB/s.