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<title>Understanding usable and unusable capacity</title>

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<h1>Understanding usable and unusable capacity</h1>
<p>Physical drive capacities influence the way you create pools and logical devices.
  Drives in an pool can be of different capacities (1 GB, or 2 GB, for example) or the
  same capacity.
  </p>

<p>Generally speaking,
  <b>usable</b> capacity is the same as the total <b>disk</b> capacity. (A small area, known as the
  <a href="graidsig.htm">raid signature</a> is used to store administrative data.) After you define a logical device, you can use
  the remaining space to define another logical device. The <a href="gsegment.htm">segments</a>
  that make up the logical device must be the same size on each physical drive.</p>

  <p>
  For example, you can group three 2 GB segments on three physical drives with different capacities,
  and three 1 GB segments with the remaining space to define a 3 GB logical device. In the following diagram, the
  logical devices are labeled 1 and 2; 4 GB of usable capacity remain, 2 GB on each drive, labeled 3.</p>
<table width="44%" border="0" align="center">
  <tr>
    <td colspan="3"><font color="#FF0000"><img src="images/ccode.gif" width="380" height="160"></font></td>
  </tr>
  <tr>
    <td > <table width="106%" border="0" align="left" height="26">
        <tr>
          <td width="20%"><b>&nbsp;&nbsp;2 GB</b></td>
          <td align="left" width="18%"><b>2 GB</b></td>
          <td align="left" width="21%"><b>3GB</b></td>
          <td align="left" width="17%"><strong>3 GB</strong></td>
          <td align="left" width="24%"><strong>3 GB</strong></td>
        </tr>
      </table></td>
  </tr>
</table>
<h2>More information</h2>

<ul>
  <li><a href="ctotalsp.htm">Example: Total disk capacity</a></li>
    </a> </li>
</ul>

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  <a href="gportal.htm">Glossary</a> | <a href="menutoc.htm">Contents</a></div>
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