Brian Jackson wrote:
On 12/17/2010 4:29 PM, Erik Brakkee wrote:
Hi,
For a backup of data from a VM to a USB mounted disk I want to
circumvent the USB 1.1 limitations on the guest and instead copy the
data over to the host using scp/ssh. I have setup a network using
virtio and NAT like this:
<interface type='network'>
<mac address='52:54:00:6b:0d:36'/>
<source network='default'/>
<target dev='vnet1'/>
<model type='virtio'/>
<alias name='net1'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06'
function='0x0'/>
</interface>
What does that equate to in command line options? Check libvirt logs
maybe. What version of qemu-kvm? Guest details? Host details?
When I now create a 1GB file using dd and copy it over from the guest
to the host, I am seeing a performance between 25-30 MB/s.
Is it to and from the same disk? If so, maybe you could try a tmpfs in
the guest or host so you aren't constantly seeking back and forth on
the same disk.
Also have you tried something like rsyncd instead of scp? Maybe you
are hitting some sort of encryption limitation.
My question is if this is normal because I have seen others on the
internet achieve far greater speeds.
Depends on a lot of factors. Certainly raw bandwidth wise, virtio-net
is capable of a lot more than that. With vhost-net here, I can get
over 5gbps guest to host. And that's on crappy old first gen cpus (no
ept/etc.).
In any case the speeds are comparable to current USB 2.0 speeds but I
intend on using USB 3.0 so would like to get a little bit more out of
it.
What would I use to speed this up a bit futher?
Cheers
Erik
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
You are right. I was indeed not so smart of me. I was assuming that the
overhead of SSH would be negligible. However, I am seeing similar
transfer speeds when I copy a file on the localhost to the localhost
using SSH (on the host, not even on a guest). Netperf tests of the
network show much higher speeds (approx 900Mbps) so the network is not
the problem. The bottleneck is definitely SSH.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
