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I have an SSD installed, and when I'm transferring to or from an external HDD via USB 3.0 I get speeds of upwards 100mb/s.

However if I'm transferring between 2 external HDDs both on 3.0 I get a staggering 10mbs. Is this uncommon?

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You mean MB/s, right? Not Mbps. – David Schwartz Jun 2 '12 at 3:44
What kind of files are you transferring? Are there lots of small files or are they all large files? – Mokubai Jun 2 '12 at 6:24

If one of the external HDD is not SSD this is normal beacause the slower drive is creating the transfer speed limit.

Try transfering from one drive to another and then back. Is the speed "staggering 10mbs" both ways?

Otherwise if not already the case connect both devices on the motherboard USB 3.0 ports.

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The drives are the limiting factor, not the bus. What units are those? bits? bytes? If you are saying 10Mbps, then yes, it is fairly slow, so I would think that one or other drive is having problems or not connected well.

If it is 10MBps, then that is still pretty slow, but not abnormally so. Are the drives (particularly the destination drive) fragmented? If one or both drives have fragmentation, then the two heads have to move a lot more, causing a slow-down and 10MBps is not unreasonable in that situation.

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Yea, megabytes per seconds. But I'm saying that I have 3 external hard drives all USB 3.0 I have 100mbs transferring between these and my SSD. So the issue can't be the drives cause they're all capable of that speed individually. But if I'm transferring between these, so like HDD 1 to 2, speed drops to 10megabytes per sec. – Mayowa Jun 2 '12 at 4:18
Yes, because writes are always slower than reads, and when you transfer to the SSD, it writes very fast, but when you transfer to the non-SSD drive, it has to move the head around, so unless the drive is nice and clean and defragged, the thrashing can slow it down to speeds like that. It also depends on what is being transferred. Copying one, giant, defragged file will transfer much faster than lots of tiny files. Have you observed the rate going up or down or is it (somehow) constant? Did you try transferring different things? What are you using to do the transfers, Windows Explorer? – Synetech Jun 2 '12 at 4:22

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