4120-initial-differential.html

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   5 <h1>Initial qemu pull-mode differential backup</h1>
   6
   7 <ul>
   8   <li>expose the bitmap over NBD for third-party access</li>
   9   <li>create a new bitmap on each backup</li>
  10   <li>transfer which bitmap is enabled; all others are disabled</li>
  11   <li>merge sequence of bitmaps to perform differential backup</li></li>
  12 </ul>
  13
  14 <p>Time elapses
  15   <table>
  16     <tr>
  17       <td style="vertical-align: top;">
  18         <p style="font-size:20px;">Image.qcow2</p>
  19         <table class="disk">
  20           <tr>
  21             <th style="visibility:hidden;">b0</th>
  22             <th>A</th><th>-</th><th>A</th><th>B</th>
  23             <th>B</th><th>B</th><th>-</th><th>-</th>
  24           </tr>
  25           <tr style="color:green;">
  26             <td style="font-style: italic;">b0</td>
  27             <td>-</td><td>-</td><td>-</td><td>X</td>
  28             <td>X</td><td>X</td><td>-</td><td>-</td>
  29           </tr>
  30         </table>
  31       </td>
  32       <td style="vertical-align: top;">
  33         <p style="font-size:20px;">FullBackup.qcow2</p>
  34         <table class="disk">
  35           <tr>
  36             <th>A</th><th>-</th><th>A</th><th>A</th>
  37             <th>-</th><th>A</th><th>-</th><th>-</th>
  38           </tr>
  39         </table>
  40       </td>
  41     </tr>
  42   </table>
  43 </p>
  44
  45 <p class="attribution">See also this 2018 KVM Forum presentation:
  46   <a href="https://www.youtube.com/watch?v=zQK5ANionpU">Facilitating
  47     Incremental Backup</a>, Eric Blake</p>