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

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<h1>Understanding RAID level-5EE</h1>

<p>RAID level-5EE is similar to <a href="craid5.htm">RAID level-5</a> but with
  a built-in distributed spare and faster rebuild times. Like RAID level-5,
  this RAID level <a href="gs-unit.htm">stripes</a> data and <a href="gparity.htm">parity</a>
  across all of the drives in the pool. </p>
<p>RAID level-5EE offers both data protection and increased throughput. When
  an pool is assigned RAID level-5EE, the capacity of the logical device is reduced
  by the capacity of two physical drives in the pool: one for parity and one
  for the spare.
<p>The spare drive is part of the RAID level-5EE pool. The spare is interleaved
  with the parity blocks, as shown in the following example. This
  allows data to be reconstructed more quickly if a physical drive in the pool
  fails. With such a configuration, you cannot share the spare
  drive with other pools. If you want a spare drive for any other pool, you
  must have another spare drive for those pools.
<p>RAID level-5EE requires a minimum of four drives and, depending upon the level
  of firmware and the <a href="cstripe.htm">stripe size</a>, supports a maximum
  of 8 or 16 drives. RAID level-5EE is also firmware-specific.
<p> The following illustration is an example of a RAID level-5EE logical device.
<h2>RAID level-5EE example</h2>
<table width="557" border="0" cellpadding="3">
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="344">Start with four physical drives.
    </td>
    <td width="195"><div align="center"><img src="images/raid5e-a.gif" width="168" height="67">
      </div></td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="344">Create an pool using all four physical
      drives. </td>
    <td width="195"><img src="images/raid5e-b.gif" width="198" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="344">Then create a logical device within
      the pool.
      <p>&nbsp;</td>
    <td width="195"><img src="images/raid5eec.gif" width="198" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="344">The data is striped across the drives,
      creating blocks in the logical device.
      <p>The storage of the data parity (denoted by <b><sub><font size="5">*</font></sub></b>)
        is striped, and it shifts from drive to drive as it does in RAID level-5E.
      <p>The spare drive (denoted by <strong><font size="4" face="Courier New, Courier, mono">S</font></strong>)
        is<strong> </strong>interleaved with the parity blocks, and it also shifts
        from drive to drive.<strong> </strong> </td>
    <td width="195"><img src="images/raid5eed.gif" width="198" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="344"> If a physical drive fails in the
      pool, the data from the failed drive is reconstructed. The pool undergoes
      <a href="gcompact.htm">compaction</a>, and the distributed spare drive becomes
      part of the pool. The logical device remains RAID level-5EE.
      <p>When you replace the failed drive, the data for the logical device undergoes
        <a href="gexpand.htm">expansion</a> and returns to the original striping
        scheme. </td>
    <td width="195"><img src="images/raid5eef.gif" width="198" height="93"> </td>
  </tr>
</table>
<p> RAID level-5EE 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 or level-1E
        </li>
        <li>Higher performance than RAID level-5</li>
      </ul>
      <br> </td>
    <td align="LEFT" valign="TOP" width="50%"> <ul>
        <li>Lower performance than RAID level-1 and level-1E </li>
        <li>Cannot share a hot-spare drive with other logical devices </li>
        <li>Not supported on all controllers</li>
      </ul></td>
  </tr>
</table>
<p>&nbsp;</p>
<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="craid1e.htm">RAID level-1 Enhanced</a> </li>
  <li><a href="craid5.htm">RAID level-5</a> </li>
  <li><a href="craid6.htm">RAID level-6</a>
  <li><a href="craidx0.htm">RAID level-x0</a></li>
  <li><a href="craidvol.htm">RAID volumes</a></li>
</ul>

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