Add new partitions to an existing system
Adding New Partitions to an Existing Archlinux Install
You may find yourself in the situation where you either (1) want to create a new partition to give yourself more flexibility for backup operations, etc. or (2) are forced to create new partitions because your original partitions are full and you need to move data from the full partition to a new partition to free up space and allow your existing system to grow. (such as moving /srv and /var to separate partitions to free up space on your / (root) partition and provide more space for your webserver, etc.) This can be accomplished fairly easily provided you have additional free space on your disk or raid array.
Recently, I was faced with the problem of the root partition filling to capacity due to the size of my website files in /srv and having packages for both kdemod3 and kde-unstable filling /var/cache/pacman/pkg. Since I had available unpartitioned space on the dmraid array holding my Archlinux install, I decided to move /srv and /var to their own separate partitions to solve the problem. By doing this, I will free up the space currently taken by /srv and /var on the / partition while at the same time providing additional space on disk for both /srv and /var.