Re: [Qemu-block] Disconecting /dev/nbdX leaves stale partitions and device

[Richard W.M. Jones]

On Fri, Jul 27, 2018 at 09:53:32PM +0300, Nir Soffer wrote:
> I think performance is pretty good now, after I added efficient zeroing:
> https://gerrit.ovirt.org/c/92901/
> This should be available in 4.2.6.

This is great, thanks.

...
> I also tested uploading to raw disk using qemu-nbd on my dev setup with
> LIO storage over 1G nic.
> For reference, blkdiscard --zeroout takes 38.5 seconds on this setup.
> 
> imageio example upload to /dev/nbd0[1]: 40.3 seconds
> qemu-img convert to /dev/nbd0: 61.5 seconds
> qemu-img convert to nbd+unix socket with unordered writes (-W): 87.3 seconds
> qemu-img convert to nbd+unix socket: 96.1 seconds

Interesting.  Did you try nbdkit?  I'm getting much greater
performance than qemu-nbd on my laptop - in fact it's comparable to
local copying:

$ rm -f /var/tmp/sock
$ truncate -s 6442450944 output
$ nbdkit file file=output -U /var/tmp/sock -f


$ time bash -c '(qemu-img convert -p -n fedora-27.img nbd:unix:/var/tmp/sock; 
sync)'
    (100.00/100%)

real    0m9.555s
user    0m0.143s
sys     0m0.578s


$ time bash -c '( cp fedora-27.img output2; sync )'

real   0m9.254s
user   0m0.005s
sys    0m0.846s


Maybe I'm making a mistake in my test somewhere?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v