Libguestfs - Jul 2017 - read/write performance through mount point by guestmount

I create a *4x256GB-SSD RAID0(/dev/md1)* and I test the performance through
fio.
fio config:

ioengine=libaiodirect=1time_basedruntime=120ramp_time=30size=100g

The sequential read/write performance is:
>
> *read: 2000MB/swrite: 1800MB/s*

Now I make a ext4 on the RAID0(/dev/md1) and mount on /home/.
ANd I create a 100G-disk.qcow2 by guestfish.
> $guestfish
> ><fish>: disk-create disk.qcow2 qcow2 100*1024*1024*1024
> ><fish>: run
> ><fish>: mkfs ext4 /dev/sda
> ><fish>: shutdown
> ><fish>: quit
No errors showed.

I mount the disk.qcow2 on the /home/test/, and create a 50GB file.
> $dd if=/dev/zero of=/home/test/file bs=1M count=51280

Test sequential read/write again through fio and config almost the same:

ioengine=libaiodirect=1time_basedruntime=120ramp_time=30size=50g

and the testing filename is /home/test/file

and the performance is :
>
> *read: 86MB/swrite: 43MB/s*

how come the performance is so bad? almost down 95%.

My machine is: 4.4.0-83-generic, Ubuntu 16.04, x86_64 GNU/Linux

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?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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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