[libvirt-users] Slow network performance issues

[Alex Regan]

Hi,
I have a fedora21 system that's been running fine under normal network 
activity, but trying to perform a full backup of the 300GB filesystem is 
taking forever because the network speed appears to be very slow.

Using rsync, the transfer speeds reach a max of like 180kB/s. Using 
rsync to copy files on the local filesystem is greater than 55MB/s, so I 
don't think it's a disk issue.

What kind of network speed can I expect copying data across the network 
from the guest to another host on the same gigabit network?

I'm using the virtio driver:

# lsmod|grep virtio
virtio_console         28672  0
virtio_balloon         16384  0
virtio_net             32768  0
virtio_blk             20480  4
virtio_pci             24576  0
virtio_ring            20480  5 
virtio_blk,virtio_net,virtio_pci,virtio_balloon,virtio_console
virtio                 16384  5 
virtio_blk,virtio_net,virtio_pci,virtio_balloon,virtio_console

ethtool on the vnet0 interface shows the speed at only 10Mb/s. Is that 
normal? Or even changable?

I've included the qemu command-line below.

# ps ax|grep propguest
  1582 ?        Sl   25433:37 /usr/bin/qemu-system-x86_64 -machine 
accel=kvm -name propguest -S -machine pc-1.2,accel=kvm,usb=off -m 16384 
-realtime mlock=off -smp 4,sockets=4,cores=1,threads=1 -uuid 
b67e10fe-7ef0-a1ca-cecf-3f3506d54e1a -no-user-config -nodefaults 
-chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/propguest.monitor,server,nowait 
-mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc 
-no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 
-device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5 -drive 
file=/var/lib/libvirt/iso-images/Fedora-18-x86_64-DVD.iso,if=none,id=drive-ide0-1-0,readonly=on,format=raw 
-device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -drive 
file=/var/lib/libvirt/images/propguest.img,if=none,id=drive-virtio-disk0,format=qcow2 
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x6,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 
-drive 
file=/var/lib/libvirt/images/propguest-2.img,if=none,id=drive-virtio-disk2,format=raw 
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x9,drive=drive-virtio-disk2,id=virtio-disk2 
-netdev tap,fd=23,id=hostnet0,vhost=on,vhostfd=24 -device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:11:66:5a:51,bus=pci.0,addr=0x3 
-chardev pty,id=charserial0 -device 
isa-serial,chardev=charserial0,id=serial0 -chardev 
spicevmc,id=charchannel0,name=vdagent -device 
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.spice.0 
-device usb-tablet,id=input0 -spice 
port=5900,addr=127.0.0.1,disable-ticketing,seamless-migration=on -device 
qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,bus=pci.0,addr=0x2 -device 
intel-hda,id=sound0,bus=pci.0,addr=0x4 -device 
hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -device 
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8

Any ideas greatly appreciated.
Thanks,
Alex