77 lines
5.7 KiB
HTML
77 lines
5.7 KiB
HTML
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Comparison of offline storage" />
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<meta name="abstract" content="Offline storage is data that you save on media that is separate from the server." />
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<meta name="description" content="Offline storage is data that you save on media that is separate from the server." />
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<title>Comparison of offline storage</title>
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<body id="rzam4tapevsoptical"><a name="rzam4tapevsoptical"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Comparison of offline storage</h1>
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<div><p>Offline storage is data that you save on media that is separate from the server.</p>
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<p>The most common forms of offline storage are tape media and optical media. Although optical media is becoming more prevalent, tape media is the most common media. Another option that you can use is virtual
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optical media. You can use virtual optical media to save to a virtual image, which is stored on your disk units. You can then copy that image to a CD or DVD, or distribute it over your network.</p>
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<p>It is important that you understand the differences among these different forms of media while you decide which one is right for you. The following table describes some of the differences:</p>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><thead align="left"><tr><th valign="top" class="firstcol" id="d0e25">Characteristic</th>
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<th valign="top" id="d0e27">Comparison</th>
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</tr>
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</thead>
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<tbody><tr><th valign="top" class="firstcol" id="d0e31" headers="d0e25 ">Access to data</th>
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<td valign="top" headers="d0e31 d0e27 ">Optical and virtual optical storage provide random access, whereas tape provides access to data sequentially.</td>
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</tr>
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<tr><th valign="top" class="firstcol" id="d0e36" headers="d0e25 ">Capacity</th>
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<td valign="top" headers="d0e36 d0e27 ">The lowest capacity tape has a similar capacity to DVD-RAM, but midrange and high capacity tapes typically have 10 to 25 times the capacity of optical.</td>
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</tr>
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<tr><th valign="top" class="firstcol" id="d0e41" headers="d0e25 ">Compression</th>
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<td valign="top" headers="d0e41 d0e27 ">The server uses <strong>software</strong> compression to save compressed data to your optical media. This process takes considerable processing unit resources and may increase your save and restore time. Most
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tape media devices use <strong>hardware</strong> compression, which is typically faster.</td>
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</tr>
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<tr><th valign="top" class="firstcol" id="d0e52" headers="d0e25 ">Cost</th>
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<td valign="top" headers="d0e52 d0e27 ">Because you can store a larger amount of data on tape, tape has a lower cost per gigabyte.</td>
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</tr>
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<tr><th valign="top" class="firstcol" id="d0e57" headers="d0e25 ">Data transfer rates</th>
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<td valign="top" headers="d0e57 d0e27 ">Data transfer rates for tape tend to be higher than for optical media, particularly if you use tape drive compression.</td>
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</tr>
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<tr><th valign="top" class="firstcol" id="d0e62" headers="d0e25 ">Number of media passes or mounts</th>
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<td valign="top" headers="d0e62 d0e27 ">Optical media can be mounted anywhere from 50 000 to 1 million times, depending on the type of media used. The number of media passes supported by tape varies, but is typically lower than optical
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media.</td>
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</tr>
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<tr><th valign="top" class="firstcol" id="d0e67" headers="d0e25 ">Reusability</th>
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<td valign="top" headers="d0e67 d0e27 ">Not all optical media is rewritable. Some optical media are write-once media, which means that once they are written to, they cannot be reused. Tape is reusable.</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzam4tape.htm" title="This topic describes the advantages and limitations of using tape for storage. It makes some recommendations about when tape is a good choice and when you should consider other media. It also provides planning, setup, management, and troubleshooting information for stand-alone tape devices and tape libraries.">Tape</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rzam4optical.htm" title="This topic provides an overview and reference guide for IBM optical support on the iSeries server with the i5/OS operating system.">Optical storage</a></div>
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</div>
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</div>
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</body>
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