Re: [Qemu-discuss] virtual disks perfermonca <=2MB/s

[Jakob Bohm]

On 20/02/2017 12:05, Mimiko wrote:
> Hello.
>
> I've setup qemu / kvm on Debian Wheezy to host some Debian Jessie guests.
> I create disk like this:
>
> virsh vol-create-as --pool default --name root.vhd --capacity 50G 
> --format vpc
>
> Then create a virtual with this:
> virt-install --connect qemu:///system \
> --ram 2048 \
> --vcpus=4 \
> --cpuset=auto \
> --pxe \
> --os-type linux \
> --boot network,hd,menu=on \
> --disk vol=default/root.vhd,device=disk,bus=virtio,cache=writethrough \
> --network=bridge:br0,model=virtio \
> --noautoconsole \
> --hvm \
> --autostart \
> --check-cpu
>
> After setting up the system I've got poor disk performance.
> Using
>
> time dd if=/dev/zero of=/tmp/test oflag=direct bs=64k count=16000
>
> I get 1048576000 bytes (1.0 GB) copied, 397.473 s, 2.6 MB/s
What does the same test return on the host (wheezy) machine on the same
disk/partition as the vhd.

Also, consider using the native qemu disk image format (qcow2) instead
of the VHD format compatibility layer.

Finally, to help the qemu guys understand your situation, please provide
the results of these commands:

virsh dumpxml YOURVMNAME > tmp.xml
virsh domxml-to-native qemu-argv tmp.xml

/usr/bin/kvm --version
(replace /usr/bin/kvm with whatever qemu command is seen in the
domxml-to-native output)


> I've changed cache to writeback and got 20MB/s with this test. But 
> copying a file to this virtual using samba gives me no more of 2 MB/s.
>
> I've tested network connectivity with iperf and got around 750Mbit/s, 
> which I think is satisfactory.
>
> I will not want to use raw devices, as it is not self expanded and 
> will use whole space regardless of how much real data occupy.
>
> libvirtd (libvirt) 0.9.12.3
>
> Is there a way to increase disk speed to at least 50MB/s ?

Enjoy

Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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