USB limitations?

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Do Macs have a USB limit? I have a 2010 era 27" iMac. It has the 4 USB ports from the factory. I have 6 external drives, a scanner, a printer and a Blu Ray burner, plus iPad, iPhone and iPods that are occassionally connected for file transfers. My issue, is if I power up any of the externals, printer, scanner etc., either they won't work or they kick one or more of the external drives off the system. I run two USB hubs that are self powered and thinking it was a hub problem, tried several different brands of hub. All have been self powered and the problem persists with every hub.

And, I don't know if this is related, but I recently suffered a power failure after which the system wouldn't see the scanner until I switched USB cables and swapped it around different ports, to reset it. As well since the power failure, adobe Bridge seems to stall when I try to browse the external drives, yet Finder will go to the same drives and browse files without issue.
 

Raz0rEdge

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While the USB spec does support a large number of devices, the limitation is usually power draw. Using powered hubs usually alleviates that issue and allows the iMac to continue to power the maximum power it can provide to the port and any additional needed power is provided by the hub.

If you have been using powered hubs for all of your devices, they shouldn't cause problems with other devices. Do you get any messages when devices are kicked or do they quietly go away?

Was this behaviour present before the power failure or only after?
 
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While the USB spec does support a large number of devices, the limitation is usually power draw. Using powered hubs usually alleviates that issue and allows the iMac to continue to power the maximum power it can provide to the port and any additional needed power is provided by the hub.

If you have been using powered hubs for all of your devices, they shouldn't cause problems with other devices. Do you get any messages when devices are kicked or do they quietly go away?

Was this behaviour present before the power failure or only after?

The issue's been there since I added the 2nd. hub. The drives just disappear off the desktop and the scanner software gives me spinning wheel. If an external drive still shows present then Adobe Bridge gives me the spinning wheel if I try to browse, that behaviour has only occurred since the power failure.
 
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While the USB spec does support a large number of devices, the limitation is usually power draw.

Your comment just reminded of the early days of USB when Microsoft allowed one of the operating systems, can't remember which, to set the power to the USB ports. Would OSX have something similar or has that all been ironed out over the years?
 

Raz0rEdge

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The issue's been there since I added the 2nd. hub. The drives just disappear off the desktop and the scanner software gives me spinning wheel. If an external drive still shows present then Adobe Bridge gives me the spinning wheel if I try to browse, that behaviour has only occurred since the power failure.

Do all of the USB ports function? I.E., can you plug a flash drive into each of the 4 ports and have it be recognized? May also want to see if you can isolate the port that causes other devices to fall off to one of them and then avoid using that one. A power failure shouldn't necessarily cause damage unless it was associated with some sort of a lightening or some other electrical event..

Your comment just reminded of the early days of USB when Microsoft allowed one of the operating systems, can't remember which, to set the power to the USB ports. Would OSX have something similar or has that all been ironed out over the years?

I don't believe I've seen anything like that in OS X but I don't know. But since you are using external powered hubs and not getting the message "This USB device is consuming too much power..." or something similar to that, I wouldn't expect it to be a power related thing..
 
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Do all of the USB ports function? I.E., can you plug a flash drive into each of the 4 ports and have it be recognized? May also want to see if you can isolate the port that causes other devices to fall off to one of them and then avoid using that one. A power failure shouldn't necessarily cause damage unless it was associated with some sort of a lightening or some other electrical event..

Murphy's law at work, I've plugged a flash drive into every open port, loaded a blu ray into the drive and plugged in my iPad. All show, all seem to work as required. Like taking your car to the mechanic and having not act up.

I'll repost if it occurs again.
 
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And by powered hubs believe Ashwin was referring tpo using mains power hubs. Saves drawing running power from the iMac.
 

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