Hi, List, 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 would be to turn off COW attributes on VM files (since having copy on write for this kind of data is not useful). We could improve qemu-img to ensure they flag newly created images as "nocow". For those who want to use Copy-on-write (for snapshotting, to share snapshots across VM, etc..) could be able to change this behaviour by 'chattr', either globally or per VM.
I wonder could we add a patch to improve qemu-img create, to set 'nocow' flag by default on newly created images? Thanks, Chunyan
