2019-kvm-forum/8000-resize-overview.html

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   5 <h1>Using qcow2 with NBD</h1>
   6
   7 <p>
   8   <table id="border">
   9     <tr>
  10       <th style="width:8%;"></th>
  11       <th><img src="8000-raw-over-nbd.png"/></th>
  12       <th><img src="8000-qcow2-over-nbd.png"/></th>
  13     </tr>
  14     <tr>
  15       <td style="text-align:center;">Pro</td>
  16       <td>
  17         <ul>
  18           <li>Matches existing use
  19           <li>Server can start with thin qcow2, and grow it as needed
  20             with guest activity
  21         </ul>
  22       </td>
  23       <td>
  24         <ul>
  25           <li>Guest-visible size can be changed
  26           <li>Backing files
  27           <li>Dirty bitmap tracking
  28           <li>Any other qcow2 features...
  29         </ul>
  30       </td>
  31     </tr>
  32     <tr>
  33       <td style="text-align:center;">Con</td>
  34       <td>
  35         <ul>
  36           <li>Guest size is fixed
  37           <li>No access to qcow2 features from client
  38         </ul>
  39       </td>
  40       <td>
  41         <ul>
  42           <li>Server file must be preallocated, or else guest hits ENOSPC
  43           <li>Internal snapshots are unlikely to work
  44         </ul>
  45       </td>
  46     </tr>
  47   </table>
  48
  49   <p>Can we merge the best of both worlds, giving the client access to
  50   all qcow2 features, but permitting resize of the underlying file on
  51   the host?
  52 </p>
  53
  54 <p class="attribution">
  55   Clipart of computer <a href="http://clipart-library.com/clipart/76irEkBcK.htm">http://clipart-library.com/clipart/76irEkBcK.htm</a>
  56 </p>