USB Hard Drive suddently doesn't get enough power

Question

Hi there,
I'm using a Iomega Hard Drive, which has two USB connectors: the main one, and if it doesn't get enough power a second one.
Until now, I could use my hard drive with only the main one, but not anymore. If I plug both, it works though.
(When I say "now", I mean that I realised it today, but haven't been using my drive for a week or two, so it follows an update during that time, I guess).
Is that a normal / desired behavior?
Is it a kernel setting?
Is it possible to set the power of USB ports?
Thanks for any explanation / help.
Cheers,

Answer 1

Thanks, that's a usefull, detailed answer!
ewaller wrote:What are the last couple dozen lines of dmesg when after you attach your drive?
[26712.994021] usb 2-2.4: new high-speed USB device number 7 using xhci_hcd
[26713.021546] usb 2-2.4: ep 0x81 - rounding interval to 32768 microframes, ep desc says 0 microframes
[26713.021549] usb 2-2.4: ep 0x2 - rounding interval to 32768 microframes, ep desc says 0 microframes
[26713.022992] scsi11 : usb-storage 2-2.4:1.0
[26714.065198] scsi 11:0:0:0: Direct-Access     SAMSUNG  HM100UI               PQ: 0 ANSI: 2 CCS
[26714.065796] sd 11:0:0:0: [sdb] 1953525168 512-byte logical blocks: (1.00 TB/931 GiB)
[26714.066628] sd 11:0:0:0: [sdb] Write Protect is off
[26714.066633] sd 11:0:0:0: [sdb] Mode Sense: 28 00 00 00
[26714.067553] sd 11:0:0:0: [sdb] No Caching mode page present
[26714.067557] sd 11:0:0:0: [sdb] Assuming drive cache: write through
[26714.069837] sd 11:0:0:0: [sdb] No Caching mode page present
[26714.069842] sd 11:0:0:0: [sdb] Assuming drive cache: write through
[26714.097268]  sdb: sdb1 sdb2
[26714.098738] sd 11:0:0:0: [sdb] No Caching mode page present
[26714.098741] sd 11:0:0:0: [sdb] Assuming drive cache: write through
[26714.098742] sd 11:0:0:0: [sdb] Attached SCSI disk
[26724.112066] EXT4-fs (sdb1): mounting ext3 file system using the ext4 subsystem
[26724.477980] EXT4-fs (sdb1): mounted filesystem with ordered data mode. Opts: (null)
ewaller wrote:What is the output of lsusb -v with the drive attached and running?
Bus 002 Device 006: ID 059b:0571 Iomega Corp. Prestige Portable Hard Drive
Couldn't open device, some information will be missing
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0x059b Iomega Corp.
  idProduct          0x0571 Prestige Portable Hard Drive
  bcdDevice            0.00
  iManufacturer          10
  iProduct               11
  iSerial                 5
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           32
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          4
    bmAttributes         0xc0
      Self Powered
    MaxPower                2mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass         8 Mass Storage
      bInterfaceSubClass      6 SCSI
      bInterfaceProtocol     80 Bulk-Only
      iInterface              6
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
By the way, I just realise that if I plug the two usb, then remove only the one for the extra power, the device keeps working.
Thanks!