HP StorageWorks RDX Removable Disk Backup System User Guide (484933-001, June 2008)

The transfer speed capabilities of a device are often referred to by the USB specification revision in which
the transfer rate was defined. Therefore a USB 2.0 Hub will s uppor t high, full and low speed, but a
USB 1.1 hub will only support full and low speed.
The USB specification was developed and is maintained by the USB organization. The USB organization
also conducts a certification program. The USB organization will issue the USB logo to a device,
which has passed a series of tests that verify the device has correctly implemented the USB interface,
as defined by the USB specification. There are many types of USB logos depending on which features
of the USB specification a device s upp orts. A USB 2.0 log o-ed device correctly s upports high, full,
andlowspeeddatatransfer.
Setting up a
USB network
USB is very u
ser friendly. The interface automatically assigns add resses to devices; you simply need to
connect a US
BdevicetoaUSBportonasystemusingaUSBcable. IfyouhavemanyUSBdevices
or need to p
lace a device away from your system, you may place up to a maximum of five USB hubs
between the device and host system and c onnect them with additional cables.
Ifyouareusingahigh-speed(USB2.0)device,makesurethattheUSBhostatthesystemandallthe
hubs between the device and host support high-speed (USB 2.0) transfer.
When using a bulk transfer device, s uch as an R DX Removable Disk Backup System, do not use other USB
devices that will p lace restrictions on the USB bandwidth available to the bulk transfer device.
If severa
l USB devices requiring large amounts of the USB network bandwidth are to operate
simultaneously, an additional host must be added to the system. Each device must then be placed into
the separate networks star ting at the different hosts. An additional host is typically a new USB HBA,
which plu
gs into the host system’s PCI slot, creating a new USB host that resides on the network. (Note:
if sever
al USB ad apters a re placed into a system, demands on the bandwidth of the system bus will
constrain the USB devices’ performance.)
Always use USB logo-ed components in your USB network. This is the best and easiest method to
ensure r
eliable operation.
USB cables
USB cables are available in a variety of lengths. The maximum cable length is 5 meters. If you need to
place a USB device further than 5 meters from the system, you must use a hub.
Do not use USB cable extenders or couples. These are not recognized or approved by the USB
organization. The USB specification does not allow their use and they are likely to reduce the reliability of
the USB network or cause it not to work completely.
Internal and external USB devices use the same USB cables.
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USB Configuration Guide