If you just want to replicate the server A qcow2 images on the server B, but they don't have to be accessed at the same time on both A and B, then you may use DRBD with any file system on it (like ext4), running as Primary on A and Secondary on B. When A fails you will be able to switch DRBD on B to Primary and use the images there.
In case you want those images available and used on A and B at the same time – then this will be more tricky. A clustered file system may help, but I don't think performance will be right.
If you just want to make a one time copy of the images, then just stop the VMs on A, copy the images with scp/rsync/over-NFS/whatever. If the VMs must be running on A, then, for a consistent image, you will need to make some kind of snapshot. I don't know KVM and QCOW2, but maybe they provide some snapshot functionality. If not, then LVM snapshots may have if you store the images on an LVM volume.