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<title>Understanding RAID level-5</title>

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<h1>Understanding RAID level-5 </h1>
<p>RAID level-5 <a href="gs-unit.htm">stripes</a> data and <a href="gparity.htm">parity</a>
  across all drives in the pool. </p>
<p>RAID level-5 offers both data protection and increased throughput. When you
  assign RAID level-5 to an pool, the capacity of the pool is reduced by the
  capacity of one drive (for data-parity storage). RAID level-5 gives you higher
  capacity than RAID level-1, but RAID level-1 offers better performance.
<p> RAID level-5 requires a minimum of three drives and, depending upon the level
  of firmware and the <a href="cstripe.htm">stripe size</a>, supports a maximum of 16 drives.
<p>The following illustration is an example of a RAID level-5 logical device. </p>
<h2>RAID level-5 example</h2>
<table width="497" border="0" cellpadding="3">
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="289">Start with four physical drives.
    </td>
    <td width="190"><img src="images/raidl5-a.gif" width="189" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="289">Create an pool using three of the
      physical drives, leaving the fourth as a hot-spare drive. </td>
    <td width="190"><img src="images/raidl5-b.gif" width="189" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="289">Then create a logical device within
      that pool. </td>
    <td width="190"><img src="images/raidl5-c.gif" width="189" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="289">The data is striped across the drives,
      creating blocks.
      <p>Notice that the storage of the data parity (denoted by<b><sub><b><sub>
        <font size="5">*</font></sub></b></sub></b>) also is striped, and it shifts
        from drive to drive.
      <p>A parity block (<b><sub><b><sub><font size="5">*</font></sub></b></sub></b>)
        contains a representation of the data from the other blocks in the same
        stripe. For example, the parity block in the first stripe contains data
        representation of blocks 1 and 2.
      <p>
    </td>
    <td width="190"><img src="images/raidl5-d.gif" width="189" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="289"> If a physical drive fails in the
      pool, the data from the failed physical drive is reconstructed onto the
      hot-spare drive. <br>
    </td>
    <td width="190"><img src="images/raidl5-e.gif" width="200" height="105"> </td>
  </tr>
</table>
<p>RAID level-5 offers the following advantages and disadvantages. <br>
<table  BORDER>
  <tr bgcolor="#C0C0C0">
    <th align="LEFT" valign="BOTTOM" width="50%">Advantages </th>
    <th align="LEFT" valign="BOTTOM" width="50%">Disadvantages </th>
  </tr>
  <tr>
    <td align="LEFT" valign="TOP" width="50%">
      <ul>
        <li>100% data protection </li>
        <li>Offers more physical drive storage capacity than RAID level-1
        </li>
      </ul>
      <br>
    </td>
    <td align="LEFT" valign="TOP" width="50%">Lower performance than RAID level-1
 </td>
  </tr>
</table>
<h2>More information</h2>
<ul>
  <li><a href="craidint.htm">Understanding RAID technology</a></li>
  <li><a href="cstripe.htm">Understanding stripe size</a></li>
  <li><a href="cselraid.htm">Selecting a RAID level</a></li>
  <li><a href="craid0.htm">RAID level-0</a></li>
  <li><a href="craid1.htm">RAID level-1</a></li>
  <li><a href="craid6.htm">RAID level-6</a></li>
  <li><a href="craidx0.htm">RAID level-x0</a></li>
  <li><a href="craidvol.htm">RAID volumes</a></li>
</ul>

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