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

From: Mimiko
Subject: Re: [Qemu-discuss] virtual disks perfermonca <=2MB/s
Date: Mon, 20 Feb 2017 15:07:59 +0200
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1

On 20.02.2017 13:13, Vincenzo Romano wrote:
I could be wrong, but are you willing to run a VM with a disk image
If not, why are you quoting your network throughput?

No, I do not share a disk image via cifs/samba. This is a test machine, mostly 
used for compiling, and I shared / folder to browse all files.

First I've thought that it was a network problem, as I had problem setting 
networking. And I verified.

> Could you please try (on a separate test VM) raw and qcow2?

This VM was setup 2 days ago with latest Debian updates for Jessie.
I've created a raw disk of 10GB and attached to VM and mounted it. The speed is 
same - 2MB.
As per same cifs/samba access to / on the host - the speed is 180MB+, as there 
are 2 network interfaces in alb bond.

> In understand your concerns about the disk space allocation, but if
> you create a virtual disk of 50GB, I think you'd know it could grow up
> to that size and that it won't automatically shrink back.

This is my first attempt of a VM on qemu after a lot of years using Hyper-V 
2008 R2.
In Hyper-V I have little performance loose compared to direct host's disk access, and virtual disks can be compacted using gui command. I think that periodically I can recompact virtual disk using qemu/kvm/libvirt tools or Hyper-V in case of vhc/vhd (theoretically, as I've never reached initial limit, but I have chance to store more virtual disks for multiple VMs)

> Please, elaborate more on your environment and objectives.

It will be for compiling and testing. Thats why I mentioned that 50MB is ok.

On 20.02.2017 13:37, Jakob Bohm wrote:
> What does the same test return on the host (wheezy) machine on the same
> disk/partition as the vhd.

The host can handle 180MB+

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

I've tried raw and the speed is same.

> virsh domxml-to-native qemu-argv tmp.xml
LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin HOME=/ QEMU_AUDIO_DRV=none /usr/bin/kvm -S -M pc-1.1 -enable-kvm -m 2048 -smp 4,sockets=4,cores=1,threads=1 -name srv -uuid c23810c8-fe96-12df-5769-5a7a80c3c35f -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/srv.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot order=cn,menu=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=/vdisks/root.vhd,if=none,id=drive-virtio-disk0,format=vpc,cache=writeback -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 -netdev tap,id=hostnet0 -device rtl8139,netdev=hostnet0,id=net0,mac=00:00:00:00:00:00 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -vnc -vga cirrus -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8

> /usr/bin/kvm --version
QEMU emulator version 1.1.2 (qemu-kvm-1.1.2+dfsg-6+deb7u19, Debian), Copyright 
(c) 2003-2008 Fabrice Bellard

> virsh dumpxml YOURVMNAME > tmp.xml
<domain type='kvm' id='10'>
  <memory unit='KiB'>2097152</memory>
  <currentMemory unit='KiB'>2097152</currentMemory>
  <vcpu placement='static'>4</vcpu>
    <type arch='x86_64' machine='pc-1.1'>hvm</type>
    <boot dev='hd'/>
    <boot dev='network'/>
    <bootmenu enable='yes'/>
  <clock offset='utc'/>
    <disk type='file' device='disk'>
      <driver name='qemu' type='vpc' cache='writeback'/>
      <source file='/vdisks/root.vhd'/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' 
    <controller type='usb' index='0'>
      <alias name='usb0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
    <interface type='bridge'>
      <mac address='52:54:00:de:83:2d'/>
      <source bridge='br0'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' 
    <serial type='pty'>
      <source path='/dev/pts/4'/>
      <target port='0'/>
      <alias name='serial0'/>
    <console type='pty' tty='/dev/pts/4'>
      <source path='/dev/pts/4'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='59081' autoport='no' listen=''>
      <listen type='address' address=''/>
      <model type='cirrus' vram='9216' heads='1'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' 
    <memballoon model='virtio'>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x08' 
  <seclabel type='none'/>

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