You can add multiple USB devices to a virtual machine when the physical devices connect to a client computer on which the vSphere Client is running. The vSphere Client must be logged in to an instance of vCenter Server that manages the ESXi host where the virtual machines reside. USB passthrough technology supports adding multiple USB devices, such as security dongles, mass storage devices, and smartcard readers to virtual machines.

The USB controller is the USB hardware chip that provides USB function to the USB ports that it manages. USB controller hardware and modules that support USB 3.0, 2.0, and USB 1.1 devices must exist in the virtual machine. Two USB controllers are available for each virtual machine. The controllers support multiple USB 3.0, 2.0, and 1.1 devices. The controller must be present before you can add USB devices to the virtual machine.

You can add up to 20 USB devices to a virtual machine. This is the maximum number of devices supported for simultaneous connection to one virtual machine.

You can add multiple devices to a virtual machine, but only one at a time. The virtual machine retains its connection to the device while in S1 standby. USB device connections are preserved when you migrate virtual machines to another host in the datacenter.

A USB device is available to only one powered-on virtual machine at a time. When a virtual machine connects to a device, that device is no longer available to other virtual machines or to the client computer. When you disconnect the device from the virtual machine or shut the virtual machine down, the device returns to the client computer and becomes available to other virtual machines that the client computer manages.

For example, when you connect a USB mass storage device to a virtual machine, it is removed from the client computer and does not appear as a drive with a removable device. When you disconnect the device from the virtual machine, it reconnects to the client computer's operating system and is listed as a removable device.

USB 3.0 devices have the following requirements and limitations:

The virtual machine that you connect the USB 3.0 device to must be configured with an xHCI controller and have a Linux guest operating system with a 2.6.35 or later kernel.

You can connect only one USB 3.0 device operating at superspeed to a virtual machine at a time.

USB 3.0 devices are available only for passthrough from a client computer to a virtual machine. They are not available for passthrough from an ESXi host to a virtual machine.

Before you connect a device to a virtual machine, make sure the device is not in use on the client computer.

If the vSphere Client disconnects from the vCenter Server or host, or if you restart or shut down the client computer, the device connection breaks. It is best to have a dedicated client computer for USB device use or to reserve USB devices connected to a client computer for short-term use, such as updating software or adding patches to virtual machines. To maintain USB device connections to a virtual machine for an extended time, use USB passthrough from an ESXi host to the virtual machine.