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I have a strange problem with my USB drive (WD Express). When I connect it to my Windows PC's only USB port, it works at high speed (USB 2.0). However, when I connect it to a USB 2.0 hub as the only device, it works only at full speed (USB 1.1). Why is it so?

Output from USBView when the USB drive is connected directly to the PC:

USB Mass Storage Device:
bcdUSB:             0x0200
bDeviceClass:         0x00
bDeviceSubClass:      0x00
bDeviceProtocol:      0x00
bMaxPacketSize0:      0x40 (64)
idVendor:           0x1058
idProduct:          0x1021
bcdDevice:          0x2002
iManufacturer:        0x01
0x0409: "Western Digital"
iProduct:             0x02
0x0409: "Ext HDD 1021"
bNumConfigurations:   0x01
ConnectionStatus: DeviceConnected
Current Config Value: 0x01
Device Bus Speed:     High
Device Address:       0x02
Open Pipes:              2

Output when the USB drive is connected through the USB 2.0 hub:

Generic USB Hub:
Device Descriptor:
bcdUSB:             0x0200
bDeviceClass:         0x09
bDeviceSubClass:      0x00
bDeviceProtocol:      0x00
bMaxPacketSize0:      0x08 (8)
idVendor:           0x05E3 (Genesys Logic, Inc.)
idProduct:          0x0606
bcdDevice:          0x0702
iManufacturer:        0x01
0x0409: "ALCOR"
iProduct:             0x02
0x0409: "USB Hub 2.0

    USB Mass Storage Device:
    bcdUSB:             0x0200
    bDeviceClass:         0x00
    bDeviceSubClass:      0x00
    bDeviceProtocol:      0x00
    bMaxPacketSize0:      0x40 (64)
    idVendor:           0x1058
    idProduct:          0x1021
    bcdDevice:          0x2002
    iManufacturer:        0x01
    0x0409: "Western Digital"
    iProduct:             0x02
    0x0409: "Ext HDD 1021"
    bNumConfigurations:   0x01
    ConnectionStatus: DeviceConnected
    Current Config Value: 0x01
    Device Bus Speed:     Full
    Device Address:       0x03
    Open Pipes:              2
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    Most likely, it's due to insufficient power. – David Schwartz Jul 5 '16 at 22:14
  • You could have a cheaply made USB 2.0 hub that doesn't have a good controller chip. Is the hub and/or the hard drive have a separate power source? If your hard drive and/or hub don't have separate power that could be an issue. – cybernard Jul 6 '16 at 2:50
  • @DavidSchwartz No, the USB hub is powered externally via 5V/3A charger. – niutech Jul 8 '16 at 11:31
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According to David (see comments) this isn't the case and I'm indeed wrong (USB hubs can and have to pass larger packets), I can't delete the answer while it's accepted.


While not 100% sure I think it's the fault of the USB hub.

Ignore the connected drive itself and look at the stats of the hub (i.e. not indented lines):

bMaxPacketSize0:      0x08 (8)

While the HDD itself reports:

bMaxPacketSize0:      0x40 (64)

So this looks to me like the hub will only be able to process 8 bytes at once; the drive could handle 64 bytes at once. (I'm not sure if it could still pass larger packets; don't think so.)

This could (should?) create additional overhead and will slow things down (by factor 8, if you're on maximum bandwidth).

  • Good catch! This could be the culprit. – niutech Jul 8 '16 at 11:38
  • The hub can have completely different properties as an endpoint from those it has as a relay. – David Schwartz Jul 8 '16 at 16:32
  • @DavidSchwartz Could you elaborate? How are packets handled in that case? Can the hub pass 64 byte packets despite being limited to 8 bytes itself? – Mario Jul 8 '16 at 16:37
  • @Mario Yes, it can and it must. – David Schwartz Jul 8 '16 at 19:27
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Could you confirm that this is a WD Elements? What's the device's model number? As the guys suggested, the drive may not be getting enough power through the hub and thus limiting its performance. Do you have other drives or USB hubs to try different combinations to see if the problem persists?

If you are doubting the drive's health you could run WD Data Lifeguard Diagnostic and see if the drive passes both the quick and the extended tests.

Captain_WD.

  • This is WDBAAU0010HBK and it passes both WD Diag tests. The USB hub is powered externally, so this is not the case. – niutech Jul 8 '16 at 11:36
  • In this case I would suspect the Hub itself as not being able to provide the necessary performance for USB2.0 performance. Have you trued other USB2.0 or USB3.0 devices on that hub? – Captain_WD Jul 11 '16 at 12:50

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