On Thu, Nov 05, 2015 at 01:10:54PM +0200, Yaniv Kaul wrote: For virt-sparsify we just use the default that the util-linux 'fstrim -m' option uses, which (according to the fstrim manual) is 0 so it will try to discard any contiguous extent. Unfortunately it's hard to tell what the best minimum free extent would be. The disk image might not be qcow2 -- if it was raw then any 4K or even 1K block could be worth freeing. Is it a lot slower if we use a smaller minimum free extent? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/