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<title>Understanding when RAID level-x0 logical devices change to the degraded state</title>

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<h1>Understanding when RAID level-x0 logical devices change state</h1>
<p>Start with four physical drives.</p>
<p>Use two physical drives to create pool A and two physical drives to create
  pool B.</p>
<p>Use arrays A and B to create spanned pool 1. As part of a spanned pool, pools
  A and B are now called &quot;subarrays.&quot;</p>
<p>A sub-logical device is created in pool A and another sub-logical device is
  created in pool B.</p>
<p>Then, create a logical device in spanned pool 1.</p>
<p>If the sub-logical device in subarray A is in the optimal state and the sub-logical device in subarray B is in the optimal state, then the logical device in spanned
  pool 1 is in the optimal state.</p>
<p>If a physical drive fails in subarray A, then the sub-logical device in subarray
  A changes to the degraded state. Subarray B is still in the optimal state. The
  logical device in spanned pool 1 changes to the degraded state.</p>
<p>If the second physical drive fails in subarray A, then the sub-logical device
  in subarray A changes to the failed state. Subarray B remains in the optimal state.
  The logical device in spanned pool 1 changes to the failed state.</p>
<p>If the sub-logical device in subarray A is in the degraded state and a physical
  drive fails in subarray B, then the sub-logical device in subarray B changes
  to the degraded state. With both sub-logical devices in the degraded state, the
  logical device in spanned pool 1 remains in the degraded state.</p>
<h2>More information</h2>
<ul>
  <li><a href="craidx0.htm">Understanding RAID level-x0</a></li>
</ul>

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