[Libguestfs] Scaling virt-df performance

Hello, I have been looking at the "virt-df" libguestfs tool to get guest-level disk used/free statistics - specifically with Qemu-KVM/Openstack. This works great for a few Openstack instances, but when I begin to scale (even to ~30 instances/guests) the performance really takes a hit. The time it takes for the command to complete seems to scale linearly with the amount of guests/domains running on the hypervisor (note - I am using "virt-df" for all guests, not specifying one at a time; although I've tried that, too). For ~30 guests, the "virt-df" command takes around 90 seconds to complete. We are looking to support a scale of 3,000-30,000 guests disk used/free. It looks like this won't be remotely possible using "virt-df". Has anyone run into this same problem or something similar and can give me some suggestions to find a workaround? Thanks, Dan Ryder