We decided not to upstream blktap3 into Xen because there isn''t much value in it in the long run: QEMU is quite sufficient for Xen and blktap3 is necessary for XenServer in the short run only; we''d like to use QEMU in XenServer, too. I''ll leave the blktap3 version that works for Xen in Bitbucket (https://bitbucket.org/tmakatos/blktap3-patches) in case anyone wants to experiment. Blktap3 development for XenServer will continue on a blktap2.5 branch on github. Regarding concerns about QEMU''s VHD performance, we''re evaluating the possibility of porting blktap2.5''s VHD implementation to QEMU (the same applies for VHDx). Thanks -- Thanos Makatos Software Engineer (XenServer Storage) Citrix Systems Ltd. Cambridge, UK