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<a class="WebWorks_Breadcrumb_Link" href="Maintain_Units.7.1.html#1079448">Maintaining Units</a> &gt; <a class="WebWorks_Breadcrumb_Link" href="Maintain_Units.7.15.html#1079448">Background Tasks</a> &gt; Working with the Background Task Mode</div>
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<div class="Heading2"><a name="1079448">Working with the Backgro</a>und Task Mode</div>
<div class="BodyAfterHead"><a name="1585777">Background Task Mode is specifically designed to address the issue of </a>latency, which can cause problems for some applications, by helping you balance the rate of host I/O and efficient completion of background tasks.</div>
<div class="Heading3"><a name="1585853">About Latency and the Background Task Mode</a></div>
<div class="Body"><a name="1585854">Latency is the real or perceived delay in response time seen by the host </a>system when accessing some data. For some applications, such as streaming video and audio application, it is important to minimize the latency of read commands, so that users do not perceive a lag when viewing video or listening to audio. </div>
<div class="Body"><a name="1585855">When background tasks are active (for example, rebuild, verify, and </a>initialization), there can be increased latency, and under some circumstances, this can result in a degraded user experience or in an application failure. </div>
<div class="Body"><a name="1585856">You can set the </a><span class="UI-Element">Background Task Mode</span> to minimize latency. This mode monitors and paces the relationship between host I/Os and background tasks. You can set the Background Task Mode to either <span class="UI-Element">Adaptive</span> (the default) or <span class="UI-Element">Low Latency</span>.</div>
<div class="Body"><span class="UI-Element"><a name="1585857">Low Latency</a></span> mode minimizes the latency (delay) in reading data from the RAID unit by slowing down the background task process. In contrast, <span class="UI-Element">Adaptive</span> mode allows the firmware to adjust the interaction of background tasks with host I/Os to maximize the speed of both host I/O and background tasks. </div>
<div class="Body"><a name="1585858">If latency is not an issue in the applications you use, then using the Adaptive </a>Background Task Mode will probably meet your needs and will result in background tasks that complete faster. </div>
<div class="Heading3"><a name="1585859">Relationship of Task Mode a</a>nd Task Rate</div>
<div class="Body"><a name="1585860">The Background Task Mode works in conjunction with the Background Task </a>Rate.</div>
<div class="Figure" onclick="WebWorks_ToggleDIV(WebWorksRootPath, &quot;wwdd1585865&quot;);"><a name="1585865">Show </a>Background Task Settings on Controller Settings page<script type="text/javascript" language="JavaScript1.2">WebWorks_WriteArrow(WebWorksRootPath, "wwdd1585865", false);</script></div>
<script type="text/javascript" language="JavaScript1.2">WebWorks_WriteDIVOpen("wwdd1585865", false);</script>
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<span class="Red"> </span><a name="1585869"><img id="1585867" class="Default" src="images/3dm_background_task_settings.png" width="739" height="136" style="display: block; 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="Body"><span class="UI-Element"><a name="1585870">Background Task Rate</a></span> lets you set the relative performance of background tasks in relation to host I/O activity on a scale of <span class="UI-Element">1 to 5</span>, with 5 being the fastest background task and slowest I/O, while 1 is the fastest I/O and the slowest background task. Separate settings are available for Rebuild/Migrate and for Verify. (Initialization occurs at the Rebuild/Migrate rate.)</div>
<div class="Indent"><a name="1585874">5 = fastest background task; slowest host I/O</a></div>
<div class="Indent"><a name="1585875">4 = faster background task; slower host I/O</a></div>
<div class="Indent"><a name="1585876">3 = balanced between background tasks and host I/O</a></div>
<div class="Indent"><a name="1585877">2 = faster host I/O; slower background task</a></div>
<div class="Indent"><a name="1585878">1 = fastest host I/O; slowest background task </a></div>
<div class="Body"><a name="1585879">If you set the </a><span class="UI-Element">Background Task Mode</span> to <span class="UI-Element">Low Latency</span>, it slows down the background task process in the context of the current Task Rate setting, with a graduated pacing of host I/O versus background task I/O, 2 through 5. </div>
<div class="Body"><span class="NoteHeading"><a name="1585880">Important:</a></span> It is recommended that if you use the Background Task Mode of Low Latency, you always set the Background Task Rate to at least <span class="UI-Element">2</span> on the scale of 1 to 5. When used in conjunction with a rate of <span class="UI-Element">1</span> (fastest host I/O; slowest background task), Low Latency Mode can create a situation in which background tasks never complete, if there is continuous host I/O activity on the unit. </div>
<div class="Body"><a name="1585881">If you do select </a><span class="UI-Element">Low Latency</span> when the Rate is set to <span class="Bold0Body">1</span>, 3DM2 will display a warning, and will then continue to display a recommendation to change it until you change either the Rate to <span class="UI-Element">2</span> or greater, or until you change the Mode to <span class="UI-Element">Adaptive</span>.</div>
<div class="Figure" onclick="WebWorks_ToggleDIV(WebWorksRootPath, &quot;wwdd1659266&quot;);"><a name="1659266">Show </a>Low Latency Mode with warning when Rate=1<script type="text/javascript" language="JavaScript1.2">WebWorks_WriteArrow(WebWorksRootPath, "wwdd1659266", false);</script></div>
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<span class="Red"> </span><a name="1659270"><img id="1659268" class="Default" src="images/3dm_controller_settings_page_with_BTAP_warning-boxes.png" width="803" height="407" style="display: inline; float: none; left: 0.0; text-align: left; top: 0.0;" /></a></div>
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<span class="Red"> </span><a name="1659276">&nbsp;</a></div>
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<img src="Note.gif" alt="*" id="bullet1659273" border="0" width="27" height="34" /><a name="1659273">&nbsp;</a></div>
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<div class="CellBody"><span class="NoteHeading"><a name="1659275">Note: </a></span>The Background Task Rate and Background Task Mode settings are only relevant when there is host I/O activity. When there is no host activity, background tasks (rebuild/migrate, initialization, and verify) always run at the maximum.</div>
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<div class="BodyAfterHead"><a name="1585900">The table below </a>provides an overview of the impact of selecting different Task Rate and Task Mode settings.</div>
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<span class="Red"> </span><a name="1585951">&nbsp;</a></div>
<table id="1585901" class="Format_B" style="margin-bottom: 3.0pt; margin-right: pt; padding-left: pt; padding-right: pt; text-align: left;" cellspacing="0">
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<div class="TableTitle"><a name="1585904">Selecting Appropriate Background Task Rate and Mode</a></div>
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<div class="CellHeading"><a name="1585912">Your priority</a></div>
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<td id="tc1585914" style="background-color: Gainsboro; border-bottom-color: Black; border-bottom-style: none; border-bottom-width: thin; border-left-color: #E0E0E0; border-left-style: none; border-left-width: thin; border-right-color: #E0E0E0; border-right-style: none; border-right-width: thin; border-top-color: Black; border-top-style: none; border-top-width: thin; padding-bottom: 0.25em; padding-left: pt; padding-right: pt; padding-top: 0.25em; vertical-align: top; width: 56.39976pt;">
<div class="CellHeading"><a name="1585914">Rebuild </a>Task Rate</div>
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<td id="tc1585916" style="background-color: Gainsboro; border-bottom-color: Black; border-bottom-style: none; border-bottom-width: thin; border-left-color: #E0E0E0; border-left-style: none; border-left-width: thin; border-right-color: #E0E0E0; border-right-style: none; border-right-width: thin; border-top-color: Black; border-top-style: none; border-top-width: thin; padding-bottom: 0.25em; padding-left: pt; padding-right: pt; padding-top: 0.25em; vertical-align: top; width: 54.9pt;">
<div class="CellHeading"><a name="1585916">Task </a>Mode</div>
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<td id="tc1585918" style="background-color: Gainsboro; border-bottom-color: Black; border-bottom-style: none; border-bottom-width: thin; border-left-color: #E0E0E0; border-left-style: none; border-left-width: thin; border-right-color: #E0E0E0; border-right-style: none; border-right-width: thin; border-top-color: Black; border-top-style: none; border-top-width: thin; padding-bottom: 0.25em; padding-left: pt; padding-right: pt; padding-top: 0.25em; vertical-align: top; width: 141.90048pt;">
<div class="CellHeading"><a name="1585918">Comments</a></div>
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<div class="CellBody"><a name="1585920">Fastest rebuild time</a></div>
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<td id="tc1585922" 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="1585922">5</a></div>
</td>
<td id="tc1585924" 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="1585924">Adaptive</a></div>
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<td id="tc1585926" 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="1585926">Potential for higher latency on </a>host I/Os</div>
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<td id="tc1585928" 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="1585928">Balanced host I/O </a>and rebuild tasks</div>
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<td id="tc1585930" 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="1585930">3</a></div>
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<td id="tc1585932" 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="1585932">Adaptive</a></div>
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<td id="tc1585934" 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="1585934">Default setting</a></div>
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<div class="CellBody"><a name="1585936">Minimized host I/O </a>latency</div>
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<td id="tc1585938" 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="1585938">2</a></div>
</td>
<td id="tc1585940" 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="1585940">Low </a>Latency</div>
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<td id="tc1585942" 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="1585942">Background tasks will complete, </a>but will be slow when there are host I/Os</div>
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<td id="tc1585944" 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="1585944">Minimum host I/O </a>latency</div>
</td>
<td id="tc1585946" 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="1585946">1</a></div>
</td>
<td id="tc1585948" 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="1585948">Low </a>Latency</div>
</td>
<td id="tc1585950" 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="1585950">Background tasks may never </a>finish when there are continuous host I/Os. For example, a rebuild may never complete. </div>
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