What Is The Best Procedure To Move MySQL Data From One Disk To Another?

I have two hard disks, and I would like to move all of my MySQL data onto the second drive. My dilema is this; what is the best way to go about doing this? The tutorial I followed last night had me use cp to copy the /var/lib/mysql folder over to the second drive. However, it took ages to move one of my databases. It's a forum hosting database which has tons and tons of tables. It ran for about 5 hours and still didn't finish because I decided to stop it right there. I know it was working; but still, it took forever and I had to put it back up.

What would you do? Do you recommend say, copying just the 'mysql' database that has the users, and then taking a dump of all databases with mysqldump and moving it that way?

Also, is there any way using the cp command to continue what I started last night, but not write a database file if it hasn't chnaged at all?