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I have a USB 2.0 enclosure and a USB 3.0 enclosure. I want to transfer large files from one to the other very often.

Should I put the source drive in the 3.0, or the 2.0? Theoretically, IF each enclosure has the same write speed as it's read speed, it wouldn't matter right? That way I see it, the 2.0 should become the bottle neck either way.
However in the real world I'm sure it's different.

The 3.0 I've observed at about 90MB/s Write and 100MB/s Read.
The 2.0 I've observed at about 20MB/s Write and 30MB/s Read.

So I'm thinking it would make sense to use the 2.0 for reading and the 3.0 for writing, as 30MB/s will become the bottleneck. Can anyone correct me?

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You are correct. Since the USB 2.0 has a higher read speed than write speed, its better to use the USB 2.0 for reading. – nixda Dec 30 '12 at 23:05
@nixda--your comment does not make sense...both 2 and 3 .. in fact everything I can say has a read speed higher than a write speed. – mdpc Dec 31 '12 at 4:49
Spend 40 bucks on a second 3.0 case and take the drive out of the 2.0 an put it into the new one. – Phillip R. Dec 31 '12 at 5:07

I'm not sure it your bottleneck in either case would be the USB 2.x drives. However, in your specific READ from the USB2.x to WRITE to the 3.x device.

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