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| <h2 id=slogan>Generic SCSI Target Subsystem for Linux</h2> |
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| <h1>Comparison</h1> |
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| <li><a href="comparison.html">Features comparison</a></li> |
| <li><a href="scstvslio.html">SCST vs LIO/TCM</a></li> |
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| <h1>SCST vs LIO/TCM</h1> |
| <p><a href="http://linux-iscsi.org/" rel="nofollow">LIO</a>, |
| from recently being renamed to TCM, is another independent from SCST implementation |
| of SCSI target framework for Linux. It's started as PyX iSCSI target and then was |
| accommodated to other transports. But it's still in many kinds iSCSI-oriented. |
| You can find an example when people are not happy with it |
| <a href="http://thread.gmane.org/gmane.linux.scsi/65703/focus=66749">here</a>.</p> |
| |
| <p>LIO maintainer, Nicholas Bellinger, is very good in building personal relationships and promoting LIO, |
| although often using misleading half, less-then-half and simply deceitful statements |
| about LIO current state, capabilities and future directions as well as about its competitor, SCST. |
| For instance, he setup LIO targets comparison page with obviously wrong statements about SCST, like |
| that it isn't fully zero copy or it isn't a generic target engine (while LIO, of course, is fully |
| zero-copy and fully generic target engine). Any |
| <a href="http://sourceforge.net/mailarchive/message.php?msg_id=21741080">attempts</a> |
| to correct it were simply ignored.</p> |
| |
| <p>With those tricks Nicholas Bellinger was capable to attract key Linux kernel developers, and |
| they suddenly changed their opinion about Linux SCSI target subsystem in the opposite direction. |
| They previously asserted that |
| in-kernel SCSI target is the wrong direction, SCSI target must be in the user space, so |
| STGT is what everybody needed. Now their opinion is that SCSI target driver should be in the kernel space |
| and the only target good for them is LIO, doesn't matter that:</p> |
| |
| <ol> |
| <li><span>SCST is a lot more mature and advanced</span></li> |
| |
| <li><span>SCST from the beginning is a generic SCSI target</span></li> |
| |
| <li><span>SCST has a lot more features</span></li> |
| |
| <li><span>SCST has better performance</span></li> |
| |
| <li><span>SCST has a lot more users</span></li> |
| |
| <li><span>SCST has much bigger community</span></li> |
| |
| </ol> |
| |
| <p>So, rejecting base principles of the Linux kernel community that the best code should win, the worst |
| code was chosen.</p> |
| |
| <p>You can find more background behind choosing LIO as the mainline kernel SCSI target |
| subsystem if you read <a href="http://thread.gmane.org/gmane.linux.kernel/1078109/focus=1078310">this thread</a> |
| as well as searching for targets related topics in Linux kernel and Linux SCSI mailing lists.</p> |
| |
| <p>Particularly notable is that James Bottomley from the beginning was telling that SCST |
| can't be merged in the mainline kernel, because it doesn't offer a drop in replacement for STGT |
| to avoid having 2 target infrastructures in the kernel at the same time. But, since LIO can't |
| offer user space backend drivers and doesn't have ibmvstgt driver analog, for LIO the drop in replacement wasn't |
| a requirement, so 2.6.38+ kernels successfully have both STGT and LIO.</p> |
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