On Mon, Jul 31, 2017 at 09:49:00AM +0100, Richard W.M. Jones wrote:
> On Mon, Jul 31, 2017 at 12:20:10PM +0800, lampahome wrote:
> > I mount the disk.qcow2 on the /home/test/, and create a 50GB file.
>
> Mount the disk how?

OK, subject says using guestmount.

I'm surprised the slowdown isn't more than 95%.  It's using FUSE which
goes through an insane number of layers, see the "Update" section in
this post:

  https://rwmj.wordpress.com/2009/10/30/fuse-support-for-libguestfs/

Rich.

--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org