Does anyone have same problem with me in Opteron workstation ?

The installed OS is currently the Fedora Core3. And I have frequent problem
when I write a C-code which has a 'fwrite' function.

I am just using the function for dumping the memory data to the hard disc but
opentimes, it's too slow to finish up the writing. In my measure, it takes about
a couple of minutes to save 450MByes array.

Any suggestions would be appreciated since I am even not sure if it's a problem
with this machine or OS or my code ?