From: "Richard W.M. Jones" <rjones(a)redhat.com&gt; We were dropping the add_drive copyonread flag when using the libvirt backend. This resulted in significant performance degradation (2x-3x slower) when running virt-v2v against VMware servers. Thanks: Kun Wei. --- lib/launch-libvirt.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/lib/launch-libvirt.c b/lib/launch-libvirt.c index 948350b..72f86ba 100644 --- a/lib/launch-libvirt.c +++ b/lib/launch-libvirt.c @@ -1593,7 +1593,8 @@ construct_libvirt_xml_disk (guestfs_h *g, if (construct_libvirt_xml_disk_driver_qemu (g, data, drv, xo, format, drv->cachemode ? : "writeback", - drv->discard, false) + drv->discard, + drv->copyonread) == -1) return -1; } -- 1.8.3.1