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Question about USB speeds


cooper
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I've been thinking about creating, just for the fun of it, a RAID of SD cards. Prices are high, but not that excessive, and when you RAId them the speed should be good aswell. The only snag is USB, which maxes out at a theoretical 60 MB/s for the fastest form, with 40 MB/s quoted as an actual maximum. Obviously a USB hub won't give each port 40 MB/s, but I'm wondering about the ports on my MoBo.

Should I consider the ports on my MoBo a USB hub meaning a total over all the ports is 40 MB/s, or does each USB port there equal its own USB network yielding me 40 MB/s transfer speed per port?

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hmm, for what i know, USB hubs work on the switching method, so all speeds are at 40m, but the more u use, the more switching it does and will lower all speeds slightly, so say u had a 4 port hub, using all for, ur speeds may drop to say 35m each, due to the switching.

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The way I see it, USB becomes a network on which the total network capacity is 40 MB/s. You could add a hub, which would allow more devices on the network, but each independantly operating device on the network to still have at most 40 MB/s available however when multiple devices are active they must share the available bandwidth. Now remember that this will be a RAID. All devices on the network will be operating simultaneously. So 2-3 cards per network and you're kicking against the speed limit of USB itself if my logic here is right.

If the separate ports on the back of your MoBo each have 40 MB to divide amongst the devices attached to it, there's no problem and this might work out really well. I mean, 4 USB ports => 8 cards => 16 GB of solid state storage operating at a peak of 140 MB/s. That's not bad.

If all the ports on the machine should be considered another USB hub meaning they're all part of that same 40 MB/s network aswell, this method is clearly something not worth investigating.

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