Hi
    Looking in to implementing (CBT like) delta backup for KVM.

    The following looks promising..(last paragraph)
     http://wiki.qemu.org/Features/Snapshots2

     * In the last para, there is a mention of copy the blocks from the disk using dirty-bitmap as reference. How to accomplish this ? block-mirror with bitmap or is there a qemu-img command ? some details would be appreciated.

// backup software now reads foo.img using t0_dirty.dbmp to perform incremental backup, when finished

     * The backup after few runs in the backup store would be base image + bunch of delta blocks ? Will this be same as base disk and bunch of deltas ? or there is some special way to merge these ?

     * I am assuming this scheme (snapshot, bitmap, block merge etc.) should work with base disk in raw (non-qcow) format as well ? Right ? i.e. will it work when the storage disk is iscsi, lvm, fc ? std linux block device?

     * Are there libvirt-api/verbs for doing some of this or we will have to sue the qemu-monitor-command ?

   * What version of qemu/kvm will have the core capabilities and which min libvirt version would be sufficient ?

     Is there a better way to do incremental backup / CBT like backup than one mentioned here ?

Thanks
/Jd