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I noticed that my hard drive is 8 times faster after replugging the USB hub it is attached to. How is that possible?

My configuration:

More info:

  • I replugged the USB hub just a few seconds after unplugging it. I replugged it to the same USSB port on the laptop. I didn't do anything while it was unplugged.
  • No other programs is accessing the drive, at least not meaningfully (I monitor the disk activity via Windows Task Manager and Windows Resource Monitor).
  • I've noticed that behavior twice already over the past 4 days, so this is not a one-time fluke.

Before replugging the USB hub, the reading speed is ~37MB/s:

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After replugging the USB hub, the reading speed is ~281MB/s with the same file:

enter image description here

After replugging the USB hub, the reading speed is ~284MB/s with a different file:

enter image description here

Franck Dernoncourt
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1 Answers1

5

~37 MB/s is approximately the practical speed of a "480 Mbps" USB 2.0 connection. It implies that your hub couldn't reliably make a USB 3.x connection to the PC the first time, but successfully connected over both 2.0+3.x the second time.

The USB connector has two completely separate sets of pins for USB 2.0 and 3.x data, and the latter frequently fail to make contact in type-A ports, so it's not uncommon for devices to be detected as USB 2.0 instead.

  • The USB 3.0 pins are located at the very end, so if the connector is inserted only halfway in (or at a slight angle, or it's dirty), those pins won't make contact and the computer will only detect a USB 2.0 device.

  • Less obviously, because the USB 2.0 pins make contact before the USB 3.0 ones do, the computer waits a certain amount of time after detecting a USB 2.0 device for the 3.x connection to be established. (Or something along those lines.)

    So if you're too slow plugging in the cable all the way in and the USB 3.0 pins don't make contact within ~0.5 seconds after the USB 2.0 connection, the device will stay detected as USB 2.0 only.

    (I don't know whether this applies to hubs, given that they use 2.0 and 3.0 connections simultaneously, but it definitely applies to regular USB devices.)

grawity
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