If you have multiple hard drives connected to a USB hub, does copied data move through the computer first or directly through the USB hub itself? Today’s SuperUser Q&A post has the answers to a curious reader’s questions.

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

Photo courtesy of itBox24 (Flickr).

The Question

SuperUser reader IAmJulianAcosta wants to know if two USB hub connected drives could transfer data directly via the USB hub and completely bypass the computer:

If I connect two USB drives to an external hub and I copy data from one drive to the other, does the data go through the computer or will the USB hub manage the data? Does this have some performance benefit?

What route will the data take when being copied from one USB drive to the other?

The Answer

SuperUser contributors lzam, Luu Vinh Phuc, and fixer1234 have the answer for us. First up, lzam:

No, this will not work. All the data you are copying will need to be read by the computer from the source drive before it is copied to the target drive.

If anything, having two hard-drives connected to the same USB hub might slow things down. If you have multiple devices connected to the hub, they have to share the bandwidth.

Followed by the answer from Luu Vinh Phuc:

USB is a host-driven protocol, not a peer-to-peer standard like firewire. Drives are just devices, they are not hosts that control or decide anything. Without the host, they cannot even interact with the outside world.

Assuming that you can connect the two drives like that, how will they know which files and/or folders you want to copy? How will they know which drive to copy from and will they overwrite duplicated files? How will they behave if the drives are full?

And our final answer from fixer1234:

A USB hub is just a way to share a connection to the computer when you do not have enough USB ports for all the devices you want to connect. Devices connected to the computer through a USB hub never talk to each other. The USB hub ensures that traffic between the computer and the connected devices goes to and from the right device as if each was literally connected to a USB port on the computer.

There is no performance benefit and there may be a performance detriment. The USB hub itself is connected to the computer through a USB connection, so everything connected to the USB hub has to share the bandwidth of that connection. Hard-drives can consume a lot of the USB hub’s bandwidth and affect the performance of other devices attached to the USB hub. You generally do not want to connect hard-drives through a USB hub at all because of that.

Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

Akemi Iwaya
Akemi Iwaya has been part of the How-To Geek/LifeSavvy Media team since 2009. She has previously written under the pen name "Asian Angel" and was a Lifehacker intern before joining How-To Geek/LifeSavvy Media. She has been quoted as an authoritative source by ZDNet Worldwide.
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