no format hdd which be inserted in the lunix computer can not be identified

do you mean a USB HDD?  If so, perhaps the following App Note may help.

http://focus.ti.com/lit/an/spraap8/spraap8.pdf

It was written for DM6446, so you can skip references to setting switches and jumpers on EVM and even how to enable support on kernel.  However, the Linux mounting commands still apply.