manual/include/copying-versus-linking.html

<p>
  <dfn>Copying</dfn> and <dfn>linking</dfn> are two different methods of
  using existing audio files on the computer (or network file system)
  within a session. They differ in one key aspect:
</p>

<h2>Copying</h2>
<p>
  An existing media file is copied to the session's audio folder, and
  if necessary converted into the session's native format.
</p>
<p>
  For audio files, the format can be chosen (e.g. WAVE or Broadcast WAVE). Audio
  files will also be converted to the session sample rate if necessary (which
  can take several minutes for larger files).
</p>
<p>
  MIDI files will already be in SMF format, and are simply copied into
  the session's MIDI folder.
</p>

<h2>Linking</h2>
<p>
  A link to an existing media file somewhere on the disk is used as the
  source for a region, but the data is <strong>not copied or modified</strong>
  in any way.
</p>
<p class="warning">
  While linking is handy to conserve disk space, it means that the session
  is <dfn>no longer self-contained</dfn>. If the external file moves, it
  will become unavailable, and any changes to it from elsewhere will affect
  the session. A backup of the session directory will miss linked files.
</p>
<p>
  The <kbd class="option">Copy file to session</kbd> option in the Import
  dialog window allows to choose to copy or link files into the session:
</p>
<table>
  <tr>
    <td><kbd class="option">Copy file to session</kbd></td>
    <td>This file will be imported in the audio/MIDI folder of the session.</td>
  </tr>
  <tr>
    <td><kbd class="optoff">Copy file to session</kbd></td>
    <td>This file won't be copied.</td>
  </tr>
</table>

<p class="note">
  There is a global preference <kbd class="menu">Edit &gt; Preferences &gt;
  General &gt; Session &gt; Always copy imported files</kbd>. If it is
  enabled, linking a file will not be possible.
</p>