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How capable are USB hubs?

I have an AirPort Extreme router with a printer attached (it's not powered by USB). I want to extend this and add two hard drives (one for Time Machine and the other for EyeTV recordings).

Can a 4-port USB hub (I'm considering this one) achieve USB 2.0 speeds and power the hard drives? What difference would a self-powered vs externally-powered hub produce?

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As well as the hub do pay attention to the quality and suitability of connecting cables. – mas Jul 17 '09 at 15:33
up vote 4 down vote accepted

Ive run 3 external hds off a Belkin wall-powered hub and gotten the same speed as a direct connection, however my hard drives were all wall-powered as well. As a rule of thumb, it's definitely better to get powered USB hubs for any hard disk usage or heavy data access (bigger thumb drives, etc), while self/computer powered hubs are usually for mouse/keyboard and generally device inputs. There is no downside as far as I am aware of using a wall-powered hub, so if you have the extra cash, its always a good investment to go with external power. I personally use an old model of Belkin's hubs, and its served me well for almost 3 years now.

tl;dr: Drawing usb power is bad for lots of data transfer, grab an externally/wall powered hub and you should be fine. Try and get the hard drives themselves powered too -- the less stress on the hub, the better.

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Does this still make a difference if the HDs themselves are externally powered? I always assumed you could use an unpowered hub if all the devices you were using were self-powered. – stillinbeta Apr 23 '10 at 14:59

A self-powered USB Hub typically reinforces and repeats the signal so that you may have longer cables. It's definitely to be prefered when running heavy USB appliances such as harddrives.

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USB cable length is limited by signal roundtrip time, not signal strength, so you can't get far beyond the 5m limit, no matter what cable/hub you use. Stability problems are likely caused by devices drawing power beyond specification. – Martin May 3 '11 at 17:46

Each device reports to the hub its power requirements, and won't get initialized if it asks for more power than is available. Also, each standard USB 2.0 port can be asked to provide up to 500mA. If you have a self-powered hub, then the hub plus all devices attached must draw less than 500mA. A powered hub would be able to provide additional current to each connected device. Recommended: a powered hub, especially if you want to connect a self-powered hard drive.

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