By default, KVM (libvirtd) images on Ubuntu and most other Linux distributions are found in /var/lib/libvirt/images. This can be inconvenient if you don't have a separate /var partition that can grow over time to accommodate multiple large images.
You can simply rename the images folder to something else and then symlink to a larger space with it (e.g. ln -s /data1/libvirt/images /var/lib/libvirt/images
). That's what I used to do.
But that can lead to all sorts of unanticipated trouble. The right way to have your images on a bigger disk is to change the path for libvirt's default storage pool to a partition on that big disk, which is logically where KVM is going to create them.
First check to make sure a default pool exists: