85 lines
5.4 KiB
HTML
85 lines
5.4 KiB
HTML
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<title>Choose compression type</title>
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<body id="compression"><a name="compression"><!-- --></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">Choose compression type</h1>
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<div><p>Choose compression type explains the types of compression that
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are available.</p>
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<p>You can use compression and other capabilities to improve save performance
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and also use less media for your save. Data compression compresses data on
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the media when you perform the save operations. Data decompression reconstructs
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data when you perform a restore operation. The system ensures that information
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saved can be reconstructed exactly. No data is lost as a result of compression
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and decompression.</p>
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<p>The two main types of compression are hardware compression and software
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compression. Most tape media devices use hardware compression, which is normally
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faster than software compression. Software compression takes considerable
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processing unit resources and may increase your save and restore time. </p>
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<p>In addition to data compression, you can use compaction and optimum block
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size features to streamline your save. These features are available through
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parameters on all save commands: .</p>
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<ul><li>Data Compression (DTACPR)</li>
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<li>Data Compaction (COMPACT)</li>
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<li>Use Optimum Block Size (USEOPTBLK)</li>
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</ul>
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<p>You can see examples of the parameter values in the <a href="../cl/savsys.htm">SAVSYS</a> command description. You can also find
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more information about compression, compaction, and optimum block size in <a href="../books/sc410607.pdf" target="_blank">iSeries™ Performance Capabilities Reference</a><img src="wbpdf.gif" alt=" Link to PDF" /> </p>
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<p>If you save to save files or optical media, you also have three choices
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available for software compression: low, medium, and high. If you choose a
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higher form of compression, your save will take longer, but the resulting
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save data will usually be smaller. The following choices are available on
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the Data Compression (DTACPR) parameter of the save commands and through the <a href="../apis/QsrSave.htm">Save Object (QsrSave</a>) and <a href="../apis/qsrsavo.htm">Save Object List (QSRSAVO)</a> APIs:</p>
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<ul><li><span class="uicontrol">Low</span> — This is the default form of compression for
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save files and optical media. Low compression is usually faster than medium
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or high compression. The compressed data is usually larger than if medium
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or high compression is used. </li>
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<li><span class="uicontrol">Medium</span> — This is the default form of compression
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for optical-DVD media. Medium compression is usually slower than low compression
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but faster than high compression. The compressed data is usually smaller than
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if low compression is used and larger than if high compression is used.</li>
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<li><span class="uicontrol">High</span> — This form of compression is new at V5R2
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and is meant to be used when maximum compression is desired. High compression
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is usually noticeably slower than low and medium compression. The compressed
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data is usually smaller than if low or medium compression is used.</li>
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</ul>
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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="rzaiurzaiu290.htm" title="Read this information before you save anything on your server.">Before you save anything...</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="rzaiusavefiles.htm">Save files</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../rzam4/rzam4overview.htm">Storage Solutions</a></div>
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</div>
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