Re: [libvirt-users] Why are virsh vol-upload/vol-download so slow?
On Fri, Mar 04, 2016 at 11:14:44AM -0500, Lars Kellogg-Stedman wrote:
I was interested in using 'virsh vol-upload' and 'virsh
vol-download',
rather than mucking about directly with the filesystem. But while
simply copying the image is relatively quick:
# ls -l /var/lib/libvirt/images/centos-7-cloud.qcow2
-rw-r--r--. 1 qemu qemu 1004994560 Apr 15 2015 centos-7-cloud.qcow2
# time cp /var/lib/libvirt/images/centos-7-cloud.qcow2 /tmp/myimage.qcow2
real 0m10.829s
user 0m0.024s
sys 0m1.668s
Trying to do the same thing with `virsh vol-download` is glacial:
# time virsh vol-download --pool default centos-7-cloud.qcow2 /tmp/myimage.qcow2
I killed it after 10 minutes:
real 10m20.775s
user 10m19.451s
sys 0m1.887s
After which is was about halfway through:
# ls -l /tmp/myimage.qcow2
-rw-r--r--. 1 root root 564920248 Mar 4 11:11 /tmp/myimage.qcow2
What is up with that?
What version of libvirt ? We had an unfortunate implementation mistake
which caused us to waste tonnes of time in memmove(). versions since
1.2.19 have a fix that addresses it
commit d9c9e138f22c48626f719f880920e04c639e0177
Author: Ossi Herrala <oherrala(a)gmail.com>
Date: Mon Jul 20 12:44:32 2015 +0000
rpc: Fix slow volume download (virsh vol-download)
Use I/O vector (iovec) instead of one huge memory buffer as suggested
in https://bugzilla.redhat.com/show_bug.cgi?id=1026137#c7. This avoids
doing memmove() to big buffers and performance doesn't degrade if
source (virNetClientStreamQueuePacket()) is faster than sink
(virNetClientStreamRecvPacket()).
Resolves: http://bugzilla.redhat.com/1026137
Signed-off-by: Martin Kletzander <mkletzan(a)redhat.com>
Regards,
Daniel
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