boot process is too slow during installation

Hi,

I am trying to install the current-FreeBSD to my Vaio PCG-Z1/P but found
the installation boot process is extremely slow. It takes more than 10
minutes to finish loading the disk created from kern.flp and another 10
minutes for mfsroot.flp. Does anyone know what the problem is?

The USB floppy drive I am using is sony's PCGA-UF05. The same thing
happens with another USB floppy drive which I don't remember the model.

I also tried to boot the installation disks of 4.8R, 4.9R and 5.1R but
the result were the same.

Thanks.

Zhang Shu