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<a class="WebWorks_Breadcrumb_Link" href="3ware_Intro.2.5.html#1584775">Understanding RAID Concepts and Levels</a> &gt; RAID Concepts &gt; RAID Concepts</div>
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<div class="Heading2"><a name="1584775">RAID Concepts</a></div>
<div class="BodyAfterHead"><a name="1584776">The following concepts are important to understand when working with a </a>RAID controller:</div>
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<div class="Bullet_inner"><span class="NoteHeading"><a name="1584779">Arrays and Units</a></span>. In the storage industry, an <span class="Emphasis">array</span> refers to two or more disk drives that appear to the operating system as a single unit. When working with a RAID controller, <span class="Emphasis">unit</span> refers to an array of disks that you can configured and manage through the 3ware software. You can also use the 3ware software to configure Single-disk units.</div>
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<div class="Bullet_inner"><span class="NoteHeading"><a name="1584781">Mirroring</a></span>. Mirrored arrays (RAID 1) write data to paired drives simultaneously. If one drive fails, the data is preserved on the paired drive. Mirroring provides data protection through redundancy. In addition, mirroring using a 3ware RAID controller provides improved performance because the 3ware TwinStor® technology reads from both drives simultaneously. </div>
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<div class="Bullet_inner"><span class="NoteHeading"><a name="1584783">Striping</a></span>. Striping across disks allows data to be written and accessed on more than one drive simultaneously. Striping combines each drives capacity into one large volume. Striped disk arrays (RAID 0) achieve highest transfer rates and performance at the expense of fault tolerance. </div>
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<div class="Bullet_inner"><span class="NoteHeading"><a name="1584785">Distributed Parity</a></span>. Parity works in combination with striping on RAID 5, RAID 6, and RAID 50. Parity information is written to each of the striped drives, in rotation. If a failure occurs, you can reconstructed the data on the failed drive from the data on the other drives.</div>
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<div class="Bullet_inner"><span class="NoteHeading"><a name="1584787">Hot Swap</a></span>. The process of exchanging a drive without shutting down the system. This process is useful when you need to exchange a defective drive in a redundant unit. </div>
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<div class="Bullet_inner"><span class="NoteHeading"><a name="1584789">Array Roaming. </a></span>The process of from a controller and putting it back either on the same controller, or a different controller, and having the unit recognized as a unit. You can attach the disks to different ports without harm to the data. </div>
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<dl>
<dt>Related Topics</dt>
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<div class="RelatedTopic"><a href="3ware_Intro.2.7.html#1584812" name="1587887">Available RAID Configurations</a></div>
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<div class="RelatedTopic"><a href="3ware_Intro.2.8.html#1584955" name="1587891">Determining Which RAID Level to Use</a></div>
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<div class="RelatedTopic"><a href="GetStart.html#1103258" name="1587895">Getting Started with Your 3ware RAID Controller</a></div>
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<div class="RelatedTopic"><a href="Config_Units.6.1.html#1062869" name="1587899">Configuring Units</a></div>
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