imagecreation-fileformat.xml

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<chapter id="imagecreation-fileformat">
  <info>
    <author>
      <firstname>Owen</firstname>
      <surname>Synge</surname>
    </author>
  </info>
  <title>Virtual machine Image File Format</title>
  <para>While the virtualisation working group does not want the software to enforce 
  a single data format we do want to support as many hyper-visor technologies as possible.</para>
  <para>It is easier to support one image than many different image formats. For this 
  reason the virtualsiation working group has come up with a single recommended format.</para>
  <para>The file format is a joint decision of the working group.</para>
  <section id="imagecreation-fileformat-hvwg1">
    <title>Virtual Machine Image File Format V1</title>
    <itemizedlist>
      <listitem>Raw disk images are used as these are supported by Qemu and Xen natively.</listitem>
      <listitem>The file will be partitioned using standard x86 partitioning schema.</listitem>
      <listitem>The raw image file will be compressed with gzip to speed transfer of the images.</listitem>
      <listitem>The Virtual machine will not use LVM as this may interfere with LVM running on 
      the hyper-visor should it be necessary to mount the VM.</listitem>
    </itemizedlist>
  </section>
  <section id="imagecreation-fileformat-hvwg2">
    <title>Virtual Machine Image File Format V2</title>
    <para>Since the original disk format assumed all disk space was included in a single image 
    this caused issues for image producers wanting to produce images that would be used with 
    a variety of number of cores, Since the image would have need to be different sizes for 
    different number of cores.</para>
    <para>To resolve the issue of image size being proportional to the number of cores intended 
    to be used with any image the image file format has been changed.</para>
    <itemizedlist>
      <listitem>Raw disk images are used as these are supported by Qemu and Xen natively.</listitem>
      <listitem>The file will be partitioned using standard x86 partitioning schema.</listitem>
      <listitem>The raw image file will be compressed with gzip to speed transfer of the images.</listitem>
      <listitem>The Virtual machine will not use LVM as this may interfere with LVM running on 
      the hyper-visor should it be necessary to mount the VM.</listitem>
      <listitem>The Virtual machine will mount a dynamically created image for the scratch space.</listitem>
    </itemizedlist>
  </section>
</chapter>