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<a class="WebWorks_Breadcrumb_Link" href="Config_Units.6.1.html#2185087">Configuring Units</a> &gt; <a class="WebWorks_Breadcrumb_Link" href="Config_Units.6.8.html#2185087">Setting Unit Policies</a> &gt; Working with Read Cache Settings</div>
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<div class="Heading2"><a name="2185087">Working with Read Cache Settings</a></div>
<div class="BodyAfterHead"><a name="2185088">The Read Cache unit policy lets you enable either Basic Read Caching or </a>Intelligent Read Caching. You can also disable the Read Cache unit policy, if preferred.</div>
<div class="Body"><a name="2188075">By default, Read Cache is set to </a><span class="UI-Element">Intelligent</span>. You can change it to <span class="UI-Element">Basic</span> or to <span class="UI-Element">Disabled</span>, as appropriate.</div>
<div class="Heading3"><a name="2185089">About the Read Cache Basic and Intelligent Modes</a></div>
<div class="Body"><span class="UI-Element"><a name="2185090">Basic Mode</a></span> is used to store read cache data locally on the controller that has recently been written to media and is likely to be frequently accessed. This improves read access times for applications such as a database that can take advantage of storage caching. The read cache may be disabled without reducing performance for applications that are write intensive, or that rarely read back data recently written.</div>
<div class="Body"><span class="UI-Element"><a name="2185091">Intelligent Mode</a></span> enables the Intelligent Read Prefetch (IRP) feature. </div>
<div class="Body"><a name="2185092">The Intelligent Read Prefetch feature includes a typical read-ahead caching </a>method which is used to proactively retrieve data from media and store it locally on the controller with the anticipation that it may be requested by the host. For example, the host may read blocks 1, 2, and 3. With the read-ahead caching included in IRP, the controller will also retrieve and hold in its cache blocks 4, 5, and 6 in anticipation of getting those command requests from the host. By loading a larger set of data into the cache, chances are improved that another request can be filled by data that is already in the cache. This can be helpful with applications that are sequential in nature, such as video on demand, video surveillance playback, and restoring from a disk-to-disk backup. Performance benefits of read-ahead are especially pronounced when the host queue depth is low. In addition, this read-ahead caching also improves sequential read performance when the unit is degraded. </div>
<div class="Body"><a name="2185093">The Intelligent Read Prefetch (IRP) feature also includes an intelligent and </a>adaptive stream management layer to improve performance at higher queue depth in multiple read only or mixed read/write stream environments. The performance improvements should be seen for most RAID types regardless of the unit’s operational state (normal, degraded, and so forth).</div>
<div class="Body"><a name="2184890">Note that if Intelligent Mode is enabled, the features in Basic mode are also </a>enabled.</div>
<div class="Heading3"><a name="2188082">When to Use Each Read Cache Setting</a></div>
<div class="BodyAfterHead"><a name="2188083">The following table provides some recommendations for when to use each </a>Read Cache setting. </div>
<div class="anchor">
<span class="Red"> </span><a name="2188117">&nbsp;</a></div>
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<div class="TableTitle"><a name="2188086">Recommendations for Using Each Read Cache Setting</a></div>
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<div class="CellHeading"><a name="2188092">Use this Read Cache </a>Setting</div>
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<div class="CellHeading"><a name="2188094">For this reason</a></div>
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<div class="CellHeading"><a name="2188096">Example applications</a></div>
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<div class="CellBody"><a name="2188098">Intelligent </a></div>
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<div class="CellBody"><a name="2188100">Sequential applications, </a>with a low host command queue depth </div>
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<div class="CellBody"><a name="2188102">Video on Demand,</a></div>
<div class="CellBody"><a name="2188103">Video Surveillance </a>Playback</div>
<div class="CellBody"><a name="2188104">Disk-to-Disk Backup </a>Restores, File Server</div>
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<div class="CellBody"><a name="2188106">Basic</a></div>
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<div class="CellBody"><a name="2188108">Frequent access to </a>recently written data</div>
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<td id="tc2188110" style="background-color: WhiteSmoke; border-bottom-color: Gainsboro; border-bottom-style: solid; border-bottom-width: thin; border-left-color: Gainsboro; border-left-style: solid; border-left-width: thin; border-right-color: Gainsboro; border-right-style: solid; border-right-width: thin; border-top-color: Gainsboro; border-top-style: solid; border-top-width: thin; padding-bottom: 0.25em; padding-left: pt; padding-right: pt; padding-top: 0.25em; vertical-align: top;">
<div class="CellBody"><a name="2188110">Database</a></div>
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<div class="CellBody"><a name="2188112">Disabled</a></div>
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<div class="CellBody"><a name="2188114">Applications that produce </a>a high queue depth or perform their own read- ahead can generate enough I/O to negate the benefits of controller read caching or read-ahead. This is especially true for applications that produce a lot of random I/O.</div>
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<td id="tc2188116" style="border-bottom-color: Gainsboro; border-bottom-style: solid; border-bottom-width: thin; border-left-color: Gainsboro; border-left-style: solid; border-left-width: thin; border-right-color: Gainsboro; border-right-style: solid; border-right-width: thin; border-top-color: Gainsboro; border-top-style: solid; border-top-width: thin; padding-bottom: 0.25em; padding-left: pt; padding-right: pt; padding-top: 0.25em; vertical-align: top;">
<div class="CellBody"><a name="2188116">Online Transaction </a>Processing (OLTP)</div>
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<div class="Heading3"><a name="2188233">Changing the Read Cache Policy for Existing Units</a></div>
<div class="Body"><a name="2188234">The Read Cache policy is initially set when you create a unit. You can change </a>it later from 3DM2. </div>
<div class="ToDo"><a name="2188238">To change the Read Cache unit policy In 3DM2</a></div>
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<span class="UI-Element">1 </span>
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<div class="NumberedFirst_inner"><a name="2188239">Choose </a><span class="UI-Element">Management &gt;&gt; Controller Settings</span> from the menu bar in 3DM2.</div>
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<span class="UI-Element">2 </span>
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<div class="Numbered_inner"><a name="2188240">In the </a><span class="UI-Element">Unit Policies</span> section of the Controller Settings page, select the desired Read Cache setting.</div>
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<div class="Indent"><span class="UI-Element"><a name="2188244">Intelligent:</a></span> Enables both the Basic and Intelligent Read Prefetch (IRP) caching features.</div>
<div class="Indent"><span class="UI-Element"><a name="2188245">Basic:</a></span> Enables the Basic read caching mode for the unit.</div>
<div class="Indent"><span class="UI-Element"><a name="2188246">Disabled:</a></span> Disables the Read Cache policy for the unit.</div>
<div class="FigureIndent" onclick="WebWorks_ToggleDIV(WebWorksRootPath, &quot;wwdd2188248&quot;);"><a name="2188248">Show </a>Read Cache policy on the Controller Settings page <script type="text/javascript" language="JavaScript1.2">WebWorks_WriteArrow(WebWorksRootPath, "wwdd2188248", false);</script></div>
<script type="text/javascript" language="JavaScript1.2">WebWorks_WriteDIVOpen("wwdd2188248", false);</script>
<div class="anchor-indented"><a name="2188252"><img id="2188250" class="Default" src="images/3dm_controller_settings_with_read_cache_options-callout.png" width="803" height="534" style="display: inline; float: none; left: 0.0; text-align: left; top: 0.0;" /></a></div>
<script type="text/javascript" language="JavaScript1.2">WebWorks_WriteDIVClose();</script>
<div class="Indent"><a name="2188253">After you change the selection, the page refreshes, and a message at the </a>top confirms the change you have made.</div>
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<dl>
<dt>Related Topics</dt>
<dd>
<div class="RelatedTopic"><a href="Config_Units.6.9.html#1113091" name="2407351">Enabling and Disabling the Unit Write Cache</a></div>
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<dd>
<div class="RelatedTopic"><a href="Config_Units.6.11.html#2185080" name="2407355">Enabling or Disabling Auto-Verify for a Unit</a></div>
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<dd>
<div class="RelatedTopic"><a href="Config_Units.6.12.html#1589821" name="2407359">Setting Overwrite ECC (Continue on Source Error When Rebuilding)</a></div>
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<dd>
<div class="RelatedTopic"><a href="Config_Units.6.13.html#1173071" name="2407363">Enabling and Disabling Queuing for a Unit</a></div>
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<dd>
<div class="RelatedTopic"><a href="Config_Units.6.14.html#1113125" name="2407367">Setting the StorSave Profile for a Unit</a></div>
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<dd>
<div class="RelatedTopic"><a href="Config_Units.6.15.html#2055333" name="2407371">Rapid RAID Recovery</a></div>
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