Re: [libvirt-users] Yet another disk I/O performance issue

'dd' is rarely a meaningful performance benchmark. In particular with the way you're invoking it, you're not requesting that the OS flush data to disk - so the data will be building up in RAM which is very fast. Since your host likely has much more free RAM for I/O cache than the guest, dd in the host is able todo much more I/O to fast RAM before the OS has to start actually writing to slow disk. The guest which is likely writing to slow disk much sooner giving the lower results. At the very least you need to request use of O_DIRECT with dd so it is writing straight to disk. Or try a formal benchmark tool like iozone 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 :|