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<title>Understanding physical drive capacity and unusable capacity</title>

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<h1>Understanding physical drive capacity and unusable capacity</h1>
<p>Physical drive capacities influence the way you create pools. Drives in the
  pool can be of different capacities (1 <a href="ggb.htm">GB</a> or 2 GB, for
  example), but the controller treats them as if they all have the capacity
  of the smallest physical drive. </p>
<p>For example, if you group three 1 GB drives and one 2 GB drive into an pool,
  the total capacity of the pool is 1 GB times 4, or 4 GB, not the 5 GB physically
  available. The remaining space on the 2 GB drive is unusable capacity.</p>

<p>Conversely, if you add a smaller drive to an pool of larger drives, such as
  a 1 GB drive to a group containing three 2 GB drives, the total capacity of
  that pool is 4 GB, not the 7 GB physically available. Therefore, the optimal
  way to create pools is to use physical drives that have the same capacity.
</p>
<p>A hot-spare drive also must be at least as large as the smallest drive in the
  pool.</p>
<h2>More information</h2>

<ul>
  <li><a href="cusable.htm">Example: Usable and unusable capacity</a></li>
  <li><a href="ctotalsp.htm">Example: Total disk capacity</a></li>
  <li><a href="ccrearry.htm">Understanding creating basic pools</a></li>
</ul>

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

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<p align="right">x-1009-HSM-00-06-EN </p>

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