Thursday, April 14, 2011

Debian KVM

Kernel-based Virtual Machine (KVM) is a virtual machine implementation using the operating system's kernel (read more here). Here are few steps to install kvm in debian:


  1. Setup SSH. Read more here.
  2. Setup bridge-utils package...
    apt-get install bridge-utils
    ... and configure network interface (restart computer so network changes take place):
    auto eth0
    iface eth0 inet manual
    auto br0
    iface br0 inet static
         bridge_ports eth0
         bridge_stp off
         # 1.
         bridge_fd 0
         bridge_maxwait 0
         # 2.
         #bridge_fd 9
         #bridge_hello 2
         #bridge_maxage 12
  3. Install qemu-kvm and libvirt-bin packages:
    apt-get -y install qemu-kvm libvirt-bin
  4. Add a user that will be managing kvm to group libvirt (e.g. user1):
    adduser user1 libvirt


  1. Setup Password-less ssh login to kvm server. Read more here.
  2. Install virt-manager package:
    apt-get -y install virt-manager
  3. If your client is not going to host kvm virtual machines you can disable the following daemons:
    update-rc.d ebtables disable
    update-rc.d libvirt-bin disable
    update-rc.d libvirt-guests disable
    update-rc.d lvm2 disable
  4. Open Virtual Machine Manager from Applications > System Tools.
  5. In File menu select Add Connection. In dialog that appears ensure method ssh and user that you added on server to group libvirt).

Performance Tuning

  1. The KVM host can take benefit of KSM by finding and sharing memory blocks between vitual machines (add the following to /etc/rc.local).
    echo 100 > /sys/kernel/mm/ksm/sleep_millisecs
    echo 1 > /sys/kernel/mm/ksm/run
    You can take a look at pages sharing / shared:
    cat /sys/kernel/mm/ksm/pages_sharing
    cat /sys/kernel/mm/ksm/pages_shared
    Another useful thing is to use vhost-net kernel module to boost virtual machine network performance (ensure guest vm uses virtio network device).
    echo vhost-net >> /etc/modules
  2. The KVM linux guest IO performance can be improved by:
    • using virtio as disk bus
    • setting virtual disk performance options to: cache mode - none, IO mode - native
    • using noop IO scheduler for each guest (file /etc/default/grub):
    GRUB_CMDLINE_LINUX_DEFAULT="quiet elevator=noop"
    Update grub by issuing update-grub command.

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