We're currently trying to replace our proprietary backup software by using libvirt snapshot-create-as/blockcommit and borgbackup on raw image.

  virsh snapshot-create-as ... --disk-only
  borg create .... vmimage.raw
  virsh blockcommit ... --active --pivot

borgbackup does compression and deduplication and has a simple command line and excellent documentation (and IRC channel :).

https://www.borgbackup.org/

guestfish/libguestfs is then used if you need specific files within an image instead of a complete restore.

https://libguestfs.org/guestfish.1.html

Example dump the name of all files on all filesystems:

   guestfish --ro -i -a vmimage.raw find /

Can be used to check integrity post backup too, and may be we'll add some file indexing tools.