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USB powered hubs

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September 4, 2011 7:17:06 AM

If this question has been asked and answered elsewhere, the I apologize, I did search. On my Vista computer, I have a 7-port powered Hub (d-link) connected to 7 different powered USB external drives. These 7 Ext. drives are powered thru a standard power strip. When I turn them all on at once, often times only 4 or maybe 5 of the Ext HDD's will be recognized by the computer. They are all known good drives as I can connect them to another computer I have (Vista) and they work just fine. Now it has been suggested to me that the problem is a powered surge when all of these devices are started simultaneously it overwhelms the computers +5 volt line. This seems unbelievable to me as I would expect a powered Ext HDD connected to a powered USB hub would draw minimal to negligible power from the computer. I also have a bunch of ext. 2.5 inch drives in enclosures which draw all of their power from the powered usb hub and they all work just fine. So what say you, is there any power "spike" that overwhelms the powered hubs and enclosures or is it just the OS craping out when all of these devices come on line at once? Thanks for the feedback.

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a c 372 G Storage
September 4, 2011 1:04:00 PM

Some motherboard bios's allow for delayed startup of drives in order to prevent all devices from powering up at once. Since these are self powered external drives I don't think it would make a difference. The motherboard does need time to sense and enumerate the drives. Perhaps your one board is just slower at it than the other and runs into a conflict trying to enumerate them all at once. It's just a guess, but sounds plausible.
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September 4, 2011 8:36:01 PM

I didn't think that the BIOS or motherboard would have these capabilities. Will investigate. So you're on board with the idea that there would be negligible power drain from the motherboard with a powered hub connected to a powered ext. HDD? Thanks for the response.
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a c 372 G Storage
September 6, 2011 11:31:01 AM

Not necessarily power drain since as you said, these have their own power supply. They still need time to spin up in order for the bios to enumerate the drives as well as the OS.
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a c 342 G Storage
September 6, 2011 3:19:33 PM

I agree the explanation likely is not a power surge. It is more likely the problem that the computer's hardware and the powered hub have to handle the sudden appearance of 7 similar USB devices. Try a test. Turn all of the external drives off at each drive, then turn on the power bar. Now turn on each drive individually, waiting a couple seconds at least (maybe more) between drives. If they all come on-line cleanly, you know that giving the USB system time to enumerate them solves your problem. If that works, you'll have to find an alternative to having one switch to power up all drives at once.
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September 6, 2011 7:49:12 PM

Thanks for the reply. I have done the test of powering up 7 ext. HDD's simultaneously against turning the on one at a time, allowing the computer to "see" each drive. Seems to be no difference. I did have an occurrence off 4 of the HDD's showing activity, disappearing from the computer, and an error message "hub power overload" or some thing similar. So I guess that this would seem to indicate that the power drawn by the ext. HDD is not "negligible". Starting to think that the problems originate in these powered hubs and not the HDD's. Question: I see the activity lights blink on these ext. HDD's all the time, even when the computer is doing nothing. Is that the computer periodically re-freshing it's memory of the line status, or is it the HDD's themselves reacting to something the computer has done? Still having issues with, after a period of time, some of the hdd's that the computer had seen at power up, disappearing and no longer being recognized by the computer. I think I need to buy some better quality USB hubs.
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September 6, 2011 7:55:32 PM

Hawkeye22 said:
Not necessarily power drain since as you said, these have their own power supply. They still need time to spin up in order for the bios to enumerate the drives as well as the OS.

Thanks for the reply. The galling thing is that when I lay out 7 or 8 or so drives on the floor, every thing works perfectly, but when I install them in bookcase( lots of work running power and data cables), then they start to crap out. Think I need to get better hubs.
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a c 372 G Storage
September 6, 2011 8:07:12 PM

You didn't mention the book case earlier. If the drives or USB hub are overheating within this book case, it may cause issues. Do you have any active or passive cooling in the book case? I think I'd add an intake and exhaust fan to the book case - depending on the book case design of course.
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September 7, 2011 12:56:38 AM

I have put my hand on these book shelves installed ext. HDD,s and they didn't seem to be hotter than normal operation out in the air, say on the living room floor. Heating could be a factor in the long haul, but my failures seem to come on boot-up before heat could boot up. Thanks for the reply.
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