6.0.1

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Remote USB devices require that the hosts be able to communicate over the management network
following migration with vMotion, so the source and destination management network IP address
families must match. You cannot migrate a virtual machine from a host that is registered to vCenter
Server with an IPv4 address to a host that is registered with an IPv6 address.
Avoiding Data Loss with USB Devices
When a virtual machine connects to a physical UBS device on an ESXi host, virtual machine functions can
affect USB device behavior and connections.
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Before you hot add memory, CPU, or PCI devices, you must remove any USB devices. Hot adding these
resources disconnects USB devices, which might result in data loss.
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Before you suspend a virtual machine, make sure that a data transfer is not in progress. During the
suspend or resume process, USB devices behave as if they have been disconnected, then reconnected.
For information about suspend and resume behavior after migration with vMotion, see “Configuring
USB Devices for vMotion,” on page 141.
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Before you change the state of the arbitrator, make sure that USB devices residing on the host are not
attached to a virtual machine. If USB devices become unavailable to a virtual machine, a host
administrator might have disabled the arbitrator. When an administrator stops or disconnects the
arbitrator for troubleshooting or other purposes, USB devices attached to that host become unavailable
to the virtual machine. If a data transfer is taking place at this time, you might lose the data. To
reestablish the arbitrator, you must restart the host.
Connecting USB Devices to an ESXi Host
You can connect and chain multiple USB hubs and devices to an ESXi host. Careful planning and
knowledge of hub behavior and limitations can help ensure that your devices work optimally.
USB physical bus topology defines how USB devices connect to the host. Support for USB device
passthrough to a virtual machine is available if the physical bus topology of the device on the host does not
exceed tier seven. The first tier is the USB host controller and root hub. The last tier is the target USB device.
You can cascade up to five tiers of external or internal hubs between the root hub and the target USB device.
An internal USB hub attached to the root hub or built into a compound device counts as one tier.
The quality of the physical cables, hubs, devices, and power conditions can affect USB device performance.
To ensure the best results, keep the host USB bus topology as simple as possible for the target USB device,
and use caution when you deploy new hubs and cables into the topology. The following conditions can
affect USB behavior:
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Communication delay between the host and virtual machine increases as the number of cascading hubs
increases.
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Connecting or chaining multiple external USB hubs increases device enumeration and response time,
which can make the power support to the connected USB devices uncertain.
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Chaining hubs together also increases the chance of port and hub error, which can cause the device to
lose connection to a virtual machine.
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Certain hubs can cause USB device connections to be unreliable, so use care when you add a new hub
to an existing setup. Connecting certain USB devices directly to the host rather than to a hub or
extension cable might resolve their connection or performance issues.
NOTE To prevent additional problems, be aware of the physical constraints of long-term deployment in a
machine room environment. Small devices are easily damaged by being stepped on or knocked loose.
In some cases, you must hard reset the device and hub to restore the device to a working state.
For a list of supported USB devices for passthrough from an ESXi host to a virtual machine, see the VMware
knowledge base article at http://kb.vmware.com/kb/1021345.
vSphere Virtual Machine Administration
142 VMware, Inc.