[arch-general] system slowing down when copying files.

Hi, My system tends to slow down a lot when I copy files to and from a pen drive or even from one hard disk to another. Even my mouse cursor slows down. The system becomes almost unusable. I more than enough RAM and I am using a tiling window manager. So I am not even using a lot of RAM. Why is this happening? I can't work on my system if I run any large file copy/move operation. Please help. Thanks.