This updates the existing patch by removing 'compress'. It turns out this program isn't installed in the appliance, and in any case the compress format is long obsolete. Below are some timings. Note that even for plain gzip compression there is quite a large time penalty. Virtio-serial / the libguestfs protocol is quite efficient at copying large files around (75 megabytes/sec, only a fraction slower than 'dd' on the host). There is no multithread support in gzip or xz at the moment, so adding SMP support to the appliance probably won't make much difference, although it's worth adding it anyway. I might play with snappy and a simple RLE-based compressor next. Rich. # Newly created, empty, 100MB ext2 filesystem: $ ./run ./fish/guestfish -N fs time download /dev/vda1 >(wc -c) elapsed time: 0.65 seconds 104792576 $ ./run ./fish/guestfish -N fs time gzip-device-out /dev/vda1 >(wc -c) elapsed time: 1.08 seconds 106799 $ ./run ./fish/guestfish -N fs time xz-device-out /dev/vda1 >(wc -c) elapsed time: 9.83 seconds 18168 # On a real filesystem that is too large to fit into cache: # Filesystem Size Used Available Use% # F16x64:/dev/vg_f16x64/lv_root 5.5G 3.2G 2.2G 59% $ ./run ./fish/guestfish --ro -a /dev/vg_pin/F16x64 run : time download /dev/vg_f16x64/lv_root >(wc -c) elapsed time: 78.74 seconds 5972688896 $ ./run ./fish/guestfish --ro -a /dev/vg_pin/F16x64 run : time gzip-device-out /dev/vg_f16x64/lv_root >(wc -c) elapsed time: 274.11 seconds 1927316373 [xz case took more than 10 minutes, I didn't wait for it to finish] -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://et.redhat.com/~rjones/virt-df/