I have:

  • A laptop with one USB3 port and a few USB2 ports
  • A USB3 hub
  • Two identical USB3 hard drives

To transfer data between the two USB3 hard drives, what is the optimum arrangement?

For example, I could connect both drives to the USB3 hub and transfer data, or I could plug one into the laptop's USB3 port and another into a USB2 port.

  • Not sure if the hub affects transfer speed but transferring from usb3 device through a usb2 port does. I would suggest transferring your files using only the usb3 port. Aug 20 '16 at 17:55
  • Use a peer enabled protocol, like fire wire which has direct dma access and can transfer directly from one disk to anothe, without the pc bottleneck.
    – cde
    Aug 20 '16 at 19:14
  • @onlyforthis: How do you transfer data between one USB3 device and another USB3 device using only one USB3 port?
    – Scott
    May 7 '19 at 15:16
  • 1
    @Scott My mistake. I meant using one type of USB. Both should be, obviously, connected to two different ports but both ports should be USB 3.0. Thanks for pointing it out. Jun 10 '19 at 18:54

There are 3 potential bottlenecks for this:
1- the speed of the harddisk
2- the speed of the interface (USB, SATA)
3- the speed of the OS and the application used for copying

1- harddisks today are capable of ~ 100 MBps, notebooks HDDs as used in external 2.5" cases maybe a bit slower (60-80 MBps). You can attain this speed only when copying sequentially large files, copying many small files will need a lot of mechanical movements of the lever arm in the HDD which will reduce the transfer speed substantially.
2- if your choice is between USB3 (5000 Mbps) vs. USB2 (500 Mbps), always choose USB3. If you need 2 such ports, use a hub. The maximum transfer rate of a USB2 HDD is around 30 MBps, and on USB3 still x10.
3- if you use Windows explorer this can be very, very slow, mainly if the number of files to copy is a couple of 10.000s. Use a specialized application like TeraCopy which uses (it's own) buffering to maximize throughput. An added benefit is that it automatically checks the file integrity of the copy by calculating a checksum.

So, in short: connect both HDDs to the USB3 hub, connect the hub to the USB3 port and use a copy utility.

  • @jiggunjer: What does ‘‘just copy them one at a time using the USB 3.0 port.’’ mean?
    – Scott
    May 7 '19 at 15:19
  • What are you refering to, please? May 23 '19 at 16:25
  • I don’t recall in detail (16 days is a long time), but I guess user jiggunjer posted a comment containing that phrase, and apparently they deleted it without explanation upon being questioned.
    – Scott
    May 23 '19 at 16:39

I ran a quick experiment, testing both possible cases stated in the answer.

I found that when the two drives were connected to the hub, data transfer was two or three times faster than when one drive was using a USB3 port while the other used a USB2 port.

I won't mark this as the accepted answer - if anyone knows more about why this setup seems to be better, please post an answer.

  • 4
    3 is so much faster than 2.
    – Xavierjazz
    Aug 20 '16 at 18:08

I is obvious that two USB3 drives in USB3 ports will perform the file transfer tasks faster, because both are operating at SuperSpeed. If one drive is in USB2 port, obviously the overall file transfer performance will be limited to USB2 speeds, be it READ or WRITE speed. The USB2 speeds are always quite lower than for USB3 mode. Please note, the particular performance of drives is irrelevant here, unless it falls below 30MB/s mark, which is unlikely.

However, if two USB drives are of USB2 type, then the issue could be more interesting. The result between "two-in-a-hub" and "in different system ports" will depend on bus topology and the number of (E/x)HCI controllers in the system. If the drives are connected to DIFFERENT host controllers, the overall file transfer could be faster.

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