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I've got two external hard drives and I'm copying the contents from one to the other. Both are USB 3.0 interface. The transfer rate is around 4MB/s and I have achieved much higher transfer rates working with each drive independently. What is the problem, is it because files are temporarily being copied to the local hard drive? How can I get a reasonable speed?

I tried TeraCopy and it doesn't help much, the computer has been running over night and it's still only 50% done. By the way, feel free to recommend products. I know some people think it breaks the rules to name a specific product as they think it's advertisement but how else are you going to get the right tool if you can't name it.

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yes your suspicion is right, it makes a local copy before copying to the other hard drive – Shekhar Jan 30 '13 at 5:26
There's more files stored on the ext hd than the main hd has room for. – Celeritas Jan 30 '13 at 5:30
I'm not sure, but if you make a very simple I/O app (say in C/C++) that opens file pointers in the external hard drives themselves and you do a direct binary copy, you should achieve much better transfer rates. – im so confused Jan 30 '13 at 5:34

It may be your answer or just another troubleshooting step but, you could try a 3rd party copying software called TeraCopy

TeraCopy is free for non-commercial use only. For commercial use you need to buy a license.

Based on the suggestions in the comments above all you could need is a software solution that copies files in a different way then the built-in Windows Copy function. If it still only copies at 4MB/s then we have ruled out Windows Copy function being the cause.

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Why TeraCopy and not something else? Also, please disclose any affiliation you may have with the company or people behind it, lest this might be considered spam. – Michael Kjörling Jan 30 '13 at 15:03
I am not affiliated with TeraCopy I just happen to use it and wanted to recommend it in this case as a possible solution. I'm not really aware of other "copy/paste" applications. Based on the suggestions in the comments above all he could need is a software solution that copies files in a different way then the built-in Windows copy function. – Sean Jan 30 '13 at 16:12
EVERY file copy program will copy data from source drive to RAM, then from RAM to destination drive. – Jamie Hanrahan Mar 18 '15 at 0:43

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