On Fri, Sep 27, 2013 at 05:02:53PM +0300, Oskari Saarenmaa wrote: > Btrfs provides a copy-on-write clone ioctl so let's try to use it instead > of copying files block by block. The ioctl is executed unconditionally if > it's available and we fall back to block copying if it fails, similarly to > cp --reflink=auto. Currently the virStorageVolCreateXMLFrom method does a full allocation of storage when cloning volumes. This means applications can rely on the image having enough space when clone completes and won't get ENOSPC in the VM. AFAICT, this change to do copy-on-write changes the API to do thin provisioning of the storage during clone, so any future write on either the new or old volume may generate ENOSPC when btrfs finally copies the sector. I don't think this is a good thing. I think applications should have to explicitly request copy-on-write behaviour for the clone so they know the implications. Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list