4040-initial-incremental.html

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   5 <h1>Initial qemu push-mode incremental backup</h1>
   6
   7 <ul>
   8   <li>drive-backup introduced in 2015</li>
   9   <li>create a new bitmap with a full backup</li>
  10   <li>future incremental backups use the prior state of the bitmap to
  11     create external file, as well as reset the bitmap</li>
  12 </ul>
  13
  14 <p>More time elapses
  15   <table>
  16     <tr>
  17       <td style="vertical-align: top;">
  18         <table>
  19           <tr>
  20             <td style="font-size:20px;">Image.qcow2</td>
  21           </tr>
  22           <tr>
  23             <td>
  24               <table class="disk">
  25                 <tr>
  26                   <th>A</th><th>-</th><th>C</th><th>C</th>
  27                   <th>B</th><th>B</th><th>-</th><th>-</th>
  28                 </tr>
  29                 <tr>
  30                   <td>-</td><td>-</td><td>X</td><td>X</td>
  31                   <td>-</td><td>-</td><td>-</td><td>-</td>
  32                 </tr>
  33               </table>
  34             </td>
  35           </tr>
  36         </table>
  37       </td>
  38       <td style="vertical-align: top;">
  39         <table>
  40           <tr>
  41             <td style="font-size:20px;">FullBackup.qcow2</td>
  42           </tr>
  43           <tr>
  44             <td>
  45               <table class="disk">
  46                 <tr>
  47                   <th>A</th><th>-</th><th>A</th><th>A</th>
  48                   <th>-</th><th>A</th><th>-</th><th>-</th>
  49                 </tr>
  50               </table>
  51             </td>
  52           </tr>
  53           <tr>
  54             <td style="font-size:20px;">IncBackup1.qcow2</td>
  55           </tr>
  56           <tr>
  57             <td>
  58               <table class="disk">
  59                 <tr>
  60                   <th>-</th><th>-</th><th>-</th><th>B</th>
  61                   <th>B</th><th>B</th><th>-</th><th>-</th>
  62                 </tr>
  63               </table>
  64             </td>
  65           </tr>
  66         </table>
  67       </td>
  68     </tr>
  69   </table>
  70 </p>
  71
  72 <p class="attribution">See also this 2015 KVM Forum presentation:
  73   <a href="https://www.youtube.com/watch?v=a2BNswm_yf8">Incremental
  74     backups: Good things come in in small packages!</a>, John Snow</p>