High I/O Wait when copying/moving Files

Hi All,

I am currently experiencing a very high IO wait whenever I copy or move a large file from a directory (say /home/user1) to another directory (say /home/user2). WA percentage in top command reaches more than 50%. This disables and hangs the desktop. I read somewhere that during copying of files, large percentage of my memory is used for cache. Is it possible to set a certain amount of my memory (8 Gb) during copy operations? I know cache memory is automatically given back to the system, but I want to allocate specific amount during copy so the Redhat desktop does not experience hang and unresponsiveness.