# move /var out of the sysdisk
# so far the second disk is /dev/xvdc on /srv/xvdc
umount /srv/xvdc
mkfs.ext4 /dev/xvdc
umount /srv/xvdd
mkfs.ext4 /dev/xvdd
cd /var
find . -print | cpio -pdmua /srv/xvdc
vi /etc/fstab
/dev/xvdc	/var	ext4	defaults,noatime 0 0
/dev/xvdd /data ext4 acl,defaults,noatime 0 0
cd /
# stop any service you may have apache2 mysql (if any running)
rm -rf var
reboot