is there any way to increase disk performance ?

[Yavuz]

I have freebsd7 (amd64 bit)  and sata2 disk 7200 rpm.

it's running mail server which has services like pop3,imap,smtp and webmail 
on this machine.

When I type systat 1 -vmstat on command line, even I rarely see that disk 
usage hits 100%.
I have no problem as ram and cpu.  they is enough.

is there any way to increase disk performance without causing any problem ?