Hi, in the book of Xen there’s this small bit on copy on write on the old Xen demo CD. “...where 30 is the size of the backing (rw) storage overlay. The backing storage is actually a file in /tmp, which is mounted as a loop device and set up using LVM. /usr/sbin/create_cow creates the storage, /usr/sbin/destroy_cow deletes it. This script is called by/etc/xen/scripts/block-cow which in turn is being called by /etc/xen/scripts/block when “cow:” is specified as block device type in the Xen VM configuration” Would anyone happen to still have create_cow and block-cow around? (Or the demo CD) We’re currently working on Ceph support(Yes! more later...) and I would like to give auto-cloning images a whirl. Are there any more recent (Xen 4.2+) attempts at copy on write that worked / are in use anywhere? (I don’t care about research papers with no sources online ;) Have a nice sunday / week! Florian About Ceph support for Xen you can have a peek at https://github.com/FlorianHeigl/xen-ceph-rbd ...right now we still need to get pygrub working