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<title>Understanding RAID level-1E</title>

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<h1>Understanding RAID level-1 Enhanced</h1>
<p>RAID level-1 Enhanced (RAID level-1E) combines mirroring and data <a href="gs-unit.htm">striping</a>.
  This RAID level stripes data and copies of the data across all of the drives
  in the pool. As with the standard RAID level-1, the data is mirrored, and the
  capacity of the logical device is 50% of the pool capacity. </p>
<p>RAID level-1E has a similar profile to RAID level-1; it provides data redundancy
  and high levels of performance, but the storage capacity is diminished. However,
  RAID level-1E allows a larger number of physical drives to be used. </p>
<p> RAID level-1E 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 8 or 16 drives. </p>
<p>The following illustration is an example of a RAID level-1E logical device.</p>
<h2>RAID level-1 Enhanced example</h2>
<table border="0" cellpadding="3">
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="323">Start with three physical drives.
    </td>
    <td width="156"><img src="images/raid1e-a.gif" width="152" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="323">Create an pool using the physical
      drives. </td>
    <td width="156"><img src="images/raid1e-b.gif" width="152" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="323">Then create a logical device within
      that pool. </td>
    <td width="156"><img src="images/raid1e-c.gif" width="152" height="93"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="323">The data is striped across the drives,
      creating blocks.
      <p>Notice that the stripe labeled<b> <b><sub><b><sub><font size="5">*</font></sub></b></sub></b></b>is
        the data stripe and the stripe labeled <b><sub><b><sub><font size="5">**</font></sub></b></sub></b>
        is the copy of the preceding data stripe. Also, notice that each block
        on the mirror stripe is shifted one drive.
    </td>
    <td width="156"><img src="images/raid1e-d.gif" width="152" height="93"> </td>
  </tr>
</table>
<p>With RAID level-1E, if one of the physical drives fails, the controller
  switches read and write requests to the remaining functional drives in the RAID
  level-1E pool. </p>
<p>RAID level-1E offers the following advantages and disadvantages: <br>
</p>
<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 redundancy </li>
        <li>High performance </li>
      </ul>
      <br>
    </td>
    <td align="LEFT" valign="TOP" width="50%">Allows only 50% of the physical
      drive storage capacity to be used </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="craid5.htm">RAID level-5</a></li>
  <li><a href="craid5ee.htm">RAID level-5EE</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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