Today I experienced an issue while restarting an ESXi 5.1 host.
Boot took a very long time and was stucked on:
running usbarbitrator start
Looking for a solution I stepped into this KB: Accessing USB storage and other USB devices from the service console
Previous KB states that this issue is due to USB Arbitrator service which manages USB passthrough. This service does not support simultaneous usb connections both from usb devices and from usb service console.
After host booted up (it took almost half an hour) login to ESXi console and diasble usb arbitrator service autostart on next reboot
chkconfig usbarbitrator off
KB suggest to reboot the host, actually for me once booted up host it worked fine, so if you need to disable usb arbitrator service without rebooting
service usbarbitrator stop