Harddisk accessible only after reboot


I am running an uptodate kernel by Rober Nelson (3.8.13-bone36).
To beaglebone black I have attached a powered USB-hub and to this
hub an external harddisk (powered over one (!) usb connector by
the USB hub).

When first powering the harddisk and then the beaglebone,
the beaglebone does not see the harddisk (fstab has entries for
mounting the harddisk). The time between powering the harddisk
and the beaglebone doesn't matter...the result is alwayse the same.

When I reboot the beaglebone after that, everything works fine.

The according modules are integrated in the kernel.

How can I accomplish, that the harddisk is accessible at the first
boot of the beaglebone black ?

Thank you very much for any help in advance!
Best regards,