I found that when trying to increase the root partition /dev/sda1 which was being reported as /dev/xvda1 on centos6 i couldn't unmount the volume in order to expand the partition.
I got around this by mounting my original volume as /dev/sda1 and my snapshot as /dev/sdb. I then restarted the image and resized the /dev/sdb1 partition using parted.
Once the partition /dev/sdb1 was resized i detached both volumes and reattached the new volume to /dev/sda1 and ran resize2fs /dev/xvda1.
