On Thu, Dec 05, 2013 at 06:35:12PM +0800, Chunyan Liu wrote:
Btrfs has terrible performance when hosting VM images, even more when the guest in those VM are also using btrfs as file system. One way to mitigate this bad performance is to turn off COW attributes on VM files (since having copy on write for this kind of data is not useful).
According to 'chattr' manpage, NOCOW could be set to new or empty file only on btrfs, so this patch tries to add a --nocow option to vol-create functions and vol-clone function, so that users could have a chance to set NOCOW to a new volume if that happens to create on a btrfs like file system.
What effect / impact does setting this flag have from a functional POV ? Why would we not just unconditonally enable it on btrfs so it was fast "out of the box" ? I'm loathe to add a btrfs-specific flag to our public API. 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 :|