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I have bought a 10 port USB Hub with power, and attached that to one port at the back of my PC. Connected to the hub are ten external hard drives.

Is this set-up safe, or can it do damage to my motherboard?

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Seeing that it is externally powered, I'd be more concerned of the quality of the information going through the single USB port on your computer. If you do not have anything of value (you probably do) on the disks, you can do a stress-test copying files arbitrarily around between the disks, and some to your system and try to interrupt their work. If all you see is that it takes forever to do it, I guess you're fine. If any files are corrupted, I guess you're not. –  Henning Klevjer Oct 29 '12 at 8:30
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@HenningKlevjer: USB has tons of protection against corruption, e.g. the use of D+/D- lines, NRZI encoding and CRC32 codes. The chances of undetected corruption are billions of times lower relative to the chance of detected corruption. I.e. if you'd copy a hundred billion files and only 10 copies fail loudly, then the chance of even one file silently getting corrupted is p < 0.00000001. –  MSalters Oct 29 '12 at 10:03
    
@MSalters Thanks for pointing that out! –  Henning Klevjer Oct 29 '12 at 10:10
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up vote 2 down vote accepted

It's safe. I'd give you a more detailed answer, but I don't know what hazard you're imagining, so it's hard to know what else to say.

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Ok, I have a follow-up question if you don't mind. :) Even if it's safe (and yes, I know it is), surely at some point it becomes impractical to tack on more devices that are simultaneously transmitting/receiving data, because the port/controller's bandwidth gets exceeded? –  Karan Oct 29 '12 at 8:04
    
It depends on whether you want to access many of the devices at the same time. If you're only going to access one or two devices at a time, then it doesn't become impractical -- even to add a hundred devices. –  David Schwartz Oct 29 '12 at 8:45
    
Yep, that's why I said "simultaneously". –  Karan Oct 29 '12 at 15:57
    
@Karan: I would say no, it doesn't become impractical. No matter how many devices you have, the bandwidth available is the same. It doesn't follow that more devices require more bandwidth, even if used at the same time. (For example, if you're trying to write 40MB/s, it doesn't matter if you're writing it to a 3 disk RAID 5 array or a 32-disk RAID 5 array, the bandwidth required is essentially the same.) –  David Schwartz Oct 29 '12 at 19:40
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Sure, but that's independent of the number of devices and solely dependent on the amount of data you have to move. Adding more devices in no way reduces the amount of data you can move. How much data you have to move depends on how much work you have to do, not how many devices that data has to go to or come from. If adding more devices means adding more work that has to be done, then it will take longer to accomplish the greater amount of work. –  David Schwartz Oct 29 '12 at 20:37
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It is completely safe. The only thing: The hub MUST have separate power supply, because it will need a lot of power!

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That depends on the harddisks too. If those have external power, they won't draw power through the hub. –  MSalters Oct 29 '12 at 9:55
    
To elaborate a little on MSalters comment: You can quantify "a lot of power". USB 2.0 allows for up to 500 mA per port, so 10 ports could draw no more than 5 Amps. In practice, unless you are using bus-powered 2.5" HDDs, the disks would have their own power supplies and the hub would need to supply negligible power and so might easily operate using only the <500mA it can draw from the PC. –  RedGrittyBrick Oct 29 '12 at 10:13
    
I don't believe there is a 10-port hub out there that can provide what the spec says the ports must. My 10-port has a powerpack that is only rated for 2.5 amps--it would have to be 5 amps just to power the ports with nothing left over for the hub electronics. –  Loren Pechtel Nov 17 '12 at 17:13
    
@LorenPechtel: I'll bet that's 2.5 amps at 12 volts (30Watt). 10 USB ports at .5 A/5V would take only 25 Watt, leaving 5 Watt for the hub itself (entirely reasonable, even ignoring the fact that it can draw another 2.5 Watt from its upstream connection) –  MSalters Dec 30 '13 at 13:47
    
@MSalters All the ports must have the same ground point. –  Loren Pechtel Dec 30 '13 at 16:04
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