I used this procedure copy my Fedora Linux OS.
Boot server in rescue mode
Boot the server from CDROM with rescue mode. At the boot prompt:
Choose mount filesystem when it is asked.
Create folder under root
Mount your destination partition under
mount /dev/hdb1 /destination
Copy all of them, because all files are not used by any process you will not have any problem
cp -ar /mnt/sysimage /destination
or copy all disk
dd if=/dev/hda of=/dev/hdb
If you are copying your boot partition you have to install grub for booting system
move hdb to hda (You have to switch master slave jumpers for both of disks)
Boot with rescue mode, mount filesystem (if you have problem, you know partitin location mount /dev/sda1 /mnt/sysimage)
Now you have copy of the system...