[ovirt-devel] Backup: how to download only used extents from imageio backend

hi, im currently looking at the new incremental backup api that has been part of the 4.4 and RHV 4.4-beta release. So far i was able to create full/incremental backups and restore without any problem. Now, using the backup_vm.py example from the ovirt-engine-sdk i get the following is happening during a full backup: 1) imageio client api requests transfer 2) starts qemu-img to create a local qemu image with same size 3) starts qemu-nbd to serve this image 4) reads used extents from provided imageio source, passes data to qemu-nbd process 5) resulting file is a thin provisioned qcow image with the actual data of the VM's used space. while this works great, it has one downside: if i backup a virtual machine with lots of used extents, or multiple virtual machines at the same time, i may run out of space, if my primary backup target is not a regular disk. Imagine i want to stream the FULL backup to tape directly like backup_vm.py full [..] <vm_uuid> /dev/nst0 thats currently not possible, because qemu-img is not able to open a tape device directly, given its nature of the qcow2 format. So what iam basically looking for, is a way to download only the extents from the imageio server that are really in use, not depending on qemu-* tools, to be able to pipe the data somehwere else. Standard tools, like for example curl, will allways download the full provisioned image from the imageio backend (of course). I noticed is that it is possible to query the extents via: https://tranfer_node:54322/images/d471c659-889f-4e7f-b55a-a475649c48a6/ex... As i failed to find them, are there any existing functions/api calls that could be used to download only the used extents to a file/fifo pipe? So far, i played around with the _internal.io.copy function, beeing able to at least read the data into a in memory BytesIO stream, but thats not the solution to my "problem" :) bye, - michael