The process of moving VM's in KVM to another disk takes several steps. The first thing you need to do is setup a new storage pool on your second disk. This can be accomplished in virsh or virt-manager. Do do this in virsh you first need to create a XML file that will be referenced during the creation of the storage pool. Here is a sample XML file that you can modify for your specific system.
Once you have created your XML file use
virsh pool-define /dir/to/newpool.xml to create the KVM storage pool.
virsh pool-start command to intialize the new pool you just created. You can verify that it was created succesfully by using
virsh pool-list --all. You should get something like:
# virsh pool-list --all
Name State Autostart
default active yes
newpool active no
The last thing you need to do is turn on autostart for the new pool using the
virsh pool-autostart newpool. This configures the libvirtd service to autostart the disk when the service starts up. You can run
virsh pool-list --all again and you should now see that it says yes under the Autostart column. The last thing you can do is check that KVM is reporting the correct size and other info of the new storage pool. This info can be found using this command
virsh pool-info newpool.
Once the new pool is created you can start creating VM's on a different disk. Hope that answers your question.