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86 lines
4.8 KiB
HTML
86 lines
4.8 KiB
HTML
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<meta name="Keywords" content="Generic SCSI Target Middle Level for Linux" />
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<meta name="author" content="Daniel Fernandes"/>
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<title>SCST: Generic SCSI Target Middle Level for Linux</title>
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<div id="header">
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<div class="logoimg"></div><h1 id="logo"><span class="orange"></span></h1>
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<h2 id="slogan">SCSI Target Middle Level for Linux</h2>
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<ul>
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<li id="sponsorship"><a href="sponsorship.html">Sponsorship</a></li>
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<li><a href="index.html">Home</a></li>
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<li><a href="http://www.sourceforge.net/projects/scst">Main</a></li>
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<li><a href="targets.html">Drivers</a></li>
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<li><a href="downloads.html">Downloads</a></li>
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<li><a href="contributing.html">Contributing</a></li>
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<li id="current"><a href="scstvsstgt.html">SCST vs STGT</a></li>
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<h1>SCST vs STGT</h1>
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<p><strong><a href="http://stgt.berlios.de/">STGT</a></strong> is alternative, independent from SCST implementation
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of SCSI target framework for Linux. It has different architecture, where SCSI target state machine is placed in
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the user space, while in SCST all the processing done in the kernel. Such architecture was acknowledged as a
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"right" one by the Linux SCSI subsystem maintainers, so kernel's part of STGT quickly found its way to the kernel.
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But such architecture has two inherent problems, namely performance and complexity.
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See thread <a href="http://sourceforge.net/mailarchive/forum.php?thread_name=472F7FA4.7040303%40wpkg.org&forum_name=scst-devel">
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"Relationship between SCST and in-kernel SCSI_TGT"</a> and <a href="http://thread.gmane.org/gmane.linux.scsi/36417/focus=37273">
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this</a> message in thread "Open-FCoE on linux-scsi" for more details.</p>
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<p>See also the following important discussions:<ul>
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<li><span><a href="http://news.gmane.org/find-root.php?message_id=%3c43987F75.2000301%40vlnb.net%3e">
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"Stgt a new version of iscsi target?"</a>, especially pay attention to
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this message: <a href="http://article.gmane.org/gmane.linux.scsi/21073">
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http://article.gmane.org/gmane.linux.scsi/21073</a> for motivation why STGT's architecture was considered "right".
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</span></li>
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<li><span><a href="http://news.gmane.org/find-root.php?message_id=%3c463F36AC.3010207%40vlnb.net%3e">
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"Question for pass-through target design"</a></span></li>
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<li><span><a href="http://news.gmane.org/find-root.php?message_id=%3ce2e108260801170127w2937b2afg9bef324efa945e43%40mail.gmail.com%3e">
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"Performance of SCST versus STGT"</a> for performance comparison.</span></li>
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</ul></p>
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<p>Also you shouldn't be deceived by the fact that some (small) part of STGT was accepted in the kernel.<br>
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It doesn't mean that STGT has the <strong>"kernel quality"</strong>. In fact, STGT as a whole similarly to any other
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out-of-tree project lives on its own, hence has its own quality level, which isn't necessary better, than the
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quality level of <strong>SCST</strong>. Actually, from such important aspect of quality as simplicity, it
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might be quite contrary: e.g. SCST isn't required to support HIGHMEM (nowadays it
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isn't necessary, but required for all in-kernel components), which allowed to simplify memory management a lot.</p>
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<p>Interesting, on 2008 Linux Storage & Filesystem Workshop, namely in
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<a href="http://www.usenix.org/event/lsf08/tech/lsf08sums.pdf">"Storage Track"</a> and
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<a href="http://www.usenix.org/event/lsf08/tech/IO_bellinger.pdf">"Linux/iSCSI and a Generic Target Mode Storage
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Engine for Linux v2.6"</a> documents, a special emphasis was put on the fact that SCST has "older" design,
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while STGT has the "current" design. Well, this seems to be a good sign, because SCST opponents have come to so
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little to say against it, so they started to use psychological arguments, exploiting the fact that most people
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think that "newer" is always better.</p>
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© Copyright 2008 <b><font color="#EC981F">Vladislav Bolkhovitin & others.</font>
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Design by: <b><font color="#EC981F">Daniel Fernandes</font></b>
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