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<title>Understanding RAID level-x0</title>

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<h1>Understanding RAID level-x0</h1>
<p><b><img src="images/note.gif" width="15" height="17"> Note: </b>RAID level-x0
  is not available on all controllers. </p>
<p>RAID level-x0 refers to RAID level-10, RAID level-50, and RAID level-60. RAID level-x0 is a
  multi-level pool, or a <b>spanned pool</b>. The operating system uses the
  spanned pool logical device in the same way as a regular pool logical device.
</p>
<p>RAID level-x0 allows more physical drives in an pool. The benefits of doing
  so are larger logical devices, increased performance, and increased reliability.
  For example, RAID level-5 cannot use more than 16 physical drives in an
  pool; however, RAID 50 supports 60 drives.
<p> RAID level-x0 requires a minimum of two drives and supports a maximum of 128 drives.
<p> The following illustration is an example of a RAID level-10 logical device.
<h2>RAID level-10 example</h2>
<table width="483" border="0" cellpadding="3">
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="248">Start with six physical drives.
    </td>
    <td width="217"><img src="images/raid10-a.gif" width="208" height="68"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="248">Create three pools (labeled A,
      B, and C), each pool using two physical drives. </td>
    <td width="217"><img src="images/raid10-b.gif" width="215" height="84"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="248">Then create a <i>spanned</i> pool
      (labeled as <b><sub><b><sub><font size="5">*</font></sub></b></sub></b>)
      that spans the three pools. </td>
    <td width="217"><img src="images/raid10-c.gif" width="231" height="106"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="248">A sub-logical device is created within
      <i>each</i> pool (A, B, and C). Then the data is striped across the physical
      drives in the pool, creating blocks.
      <p>Notice that, in each pool, the data on the drive on the right is a copy
        of the data on the drive on the left. This is because the sub-logical
        drives (A, B, and C) are RAID level-1 in a RAID level-10 implementation
        (see the following table).
      <p> </td>
    <td width="217"><img src="images/raid10-d.gif" width="231" height="106"> </td>
  </tr>
  <tr valign=top>
    <td align="LEFT" valign="TOP" width="248"> <p>Then create a logical device
        within the spanned pool (<b><sub><b><sub><font size="5">*</font></sub></b></sub></b>).</p>
      <p> The data is striped across this logical device, creating blocks (<b>1</b>-<b>12</b>).
        Notice that none of these blocks are redundant. This is because the logical
        drive is RAID level-0 in a RAID level-x0 implementation (see the following
        table). </p></td>
    <td width="217"><img src="images/raid10-e.gif" width="231" height="106"></td>
  </tr>
</table>
<p>&nbsp;</p>
<table width="85%" bordercolorlight="#FFFFFF" border="1" >
  <tr valign="top" bgcolor="#C0C0C0">
    <th align="LEFT" width="21%">RAID level </th>
    <th align="LEFT" width="40%">Sub-logical device</th>
    <th align="LEFT" width="40%">Spanned pool logical device</th>
  </tr>

  <tr>
    <td align="LEFT" valign="TOP" width="21%">10 </td>
    <td align="LEFT" valign="TOP" width="40%">RAID level-1 </td>
    <td align="LEFT" valign="TOP" width="40%">RAID level-0 </td>
  </tr>

  <tr>
    <td align="LEFT" valign="TOP" width="21%">50 </td>
    <td align="LEFT" valign="TOP" width="40%">RAID level-5 </td>
    <td align="LEFT" valign="TOP" width="40%">RAID level-0 </td>
  </tr>

   <tr>
      <td align="LEFT" valign="TOP" width="21%">60 </td>
      <td align="LEFT" valign="TOP" width="40%">RAID level-6 </td>
      <td align="LEFT" valign="TOP" width="40%">RAID level-0 </td>
  </tr>
</table>
<p>With RAID level-10 and 50, if one of the physical drives fails in a sub-logical
  drive, the controller switches read and write requests to the remaining
  functional drives in the sub-logical device.

  With RAID level-60, if one or two of the physical drives fails in a sub-logical
    drive, the controller switches read and write requests to the remaining
  functional drives in the sub-logical device.
  </p>
<p>RAID level-x0 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>Supports up to 128 physical drives</li>
        <li>100% data redundancy </li>
      </ul>
      <br> </td>
    <td align="LEFT" valign="TOP" width="50%"> <ul>
        <li>Not available on all controllers </li>
      </ul>
      <br> </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="craid6.htm">RAID level-6</a></li>
  <li><a href="craidvol.htm">RAID volumes</a></li>
</ul>

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