Web updates
authorvlnb <vlnb@d57e44dd-8a1f-0410-8b47-8ef2f437770f>
Thu, 3 Dec 2009 18:43:13 +0000 (18:43 +0000)
committervlnb <vlnb@d57e44dd-8a1f-0410-8b47-8ef2f437770f>
Thu, 3 Dec 2009 18:43:13 +0000 (18:43 +0000)
git-svn-id: https://scst.svn.sourceforge.net/svnroot/scst/trunk@1374 d57e44dd-8a1f-0410-8b47-8ef2f437770f

www/target_iscsi.html

index c7a6afa..ce47a51 100644 (file)
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                                <h1>ISCSI target driver iSCSI-SCST</h1>
-                               <p><strong>ISCSI-SCST</strong> is a forked (with all respects) version of <strong>IET</strong> with updates to work 
-                               over <strong>SCST</strong> as well as with many improvements and bugfixes. The reason of fork is that the necessary 
-                               changes are intrusive and with the current <strong>IET</strong> merge policy, where only simple bugfix-like patches,
-                                which doesn't touch the core code, could be merged, it is very unlikely that they will be merged in the main 
-                                <strong>IET</strong> trunk.</p>
-                               
-                               <p><strong>ISCSI-SCST</strong> has the following major advantages over <strong>IET</strong>. They are summarized on the
-                                       <a href="comparison.html">Comparison</a> page.</p>
+                               <p><strong>ISCSI-SCST</strong> is a forked (with all respects) version of IET. Reasons of the fork were:</p>
+
                                <ul>
-                                       <li><font color="#666666">ISCSI-SCST uses full power of <strong>SCST core</strong>, hence has the following additional features:</font>
-                                        <ul>
-                                               <li><span><strong>Pass-through mode with one to many relationship</strong>, i.e. when multiple initiators can connect to
-                                               exported pass-through devices. For instance, in this mode you can safely export your parallel
-                                               <strong>SCSI tape</strong> or <strong>tape library</strong> on 
-                                               your iSCSI net and multiple initiators can share it without risk of data loss because of the 
-                                               shared usage. Existing outdated "rawio" patch for IET supports only non-enforced 1:1 
-                                               relationship, so it is unsafe to use it in multiple initiators environments.</span></li>
+                                       <li><span>To be able to use full power of <strong>SCST core</strong>.</span></li>
+                                       <li><span>To fix all the problems, corner cases issues and iSCSI standard violations IET which has.</span></li>
+                               </ul>
 
-                                               <li><span><strong>More advanced devices visibility management</strong>, when different initiators can see different set of 
-                                               devices with different access permissions from the same target.</span></li>
+                               <p>IET is a well recognized and widely used iSCSI target, but, frankly speaking, it works more or less well
+                               on fast paths and regularly used code branches only, however in many corner
+                               cases it has a lot of problems, like ignoring error processing, as it is for memory allocations,
+                               crashing itself with BUG() macro, as it is for malformed packets from initiators, possible data
+                               corruptions, because of, for instance, unsafe task management or sessions reinstatement implementations, etc.
+                               There was no way to fix all them without a fork. As the result of this effort nearly 90% of the IET kernel code was fully
+                               rewritten.</p>
+                                
+                               <p>Since ISCSI-SCST uses SCST core, it has the following additional features:</font></p>
 
-                                               <li><span><strong>O_DIRECT</strong>, i.e. <strong>"BLOCKIO on files"</strong>, mode, which has all advantages 
-                                               of BLOCKIO, but also supports files on file systems. Sometimes, in the appropriate cases, 
-                                               this mode can make performance difference in 100% or even more.</span></li>
+                               <ul>
+                                       <li><span><strong>Pass-through mode with one to many relationship</strong>, i.e. when multiple initiators can connect to
+                                       exported pass-through devices. For instance, in this mode you can safely export your parallel
+                                       <strong>SCSI tape</strong> or <strong>tape library</strong> (or <strong>VTL</strong>) on 
+                                       your iSCSI net and multiple initiators can share it without risk of data loss because of the 
+                                       shared usage. Existing outdated "rawio" patch for IET supports only non-enforced 1:1 
+                                       relationship, so it is unsafe to use it in multiple initiators environments.</span></li>
 
-                                               <li><span><strong>4KB blocks</strong> eliminate abysmal write performance caused by misaligned partitions. 
-                                               </span></li>
+                                       <li><span><strong>More advanced devices visibility management</strong>, when different initiators can see different set of 
+                                       devices with different access permissions from the same target.</span></li>
 
-                                               <li><span><strong>Virtual CD/DVD-ROMs</strong>.</span></li>     
+                                       <li><span><strong>O_DIRECT</strong>, i.e. <strong>"BLOCKIO on files"</strong>, mode, which has all advantages 
+                                       of BLOCKIO, but also supports files on file systems. Sometimes, in the appropriate cases, 
+                                       this mode can make performance difference in 100% or even more.</span></li>
 
-                                               <li><span>Ability to create target devices emulators in the <strong>user space</strong>.</span></li>
+                                       <li><span><strong>4KB blocks</strong> eliminate abysmal write performance caused by misaligned partitions. 
+                                       </span></li>
 
-                                               <li><span>Ability to create <strong>multi-transport SCSI targets</strong>, which can export (possibly, the same) 
-                                               devices over multiple transports.</span></li>                                                                                                                            
-                                        </ul>                                   
-                                        </li>
+                                       <li><span><strong>Virtual CD/DVD-ROMs</strong>.</span></li>     
 
-                                        <li><span>ISCSI-SCST has many code improvements and cleanups, including stability
-                                         and iSCSI RFC violations fixes. 
-                                         IET works well on "fast" paths and regularly used code branches, but in many corner
-                                         cases it has various problems, from simply ignoring error processing, as it is for memory 
-                                         allocations, and crashing itself with BUG() macro, as it is for malformed packets from initiators, to possible data
-                                         corruptions, because of, for instance, unsafe task management or sessions reinstatement implementations.</span></li>
+                                       <li><span>Ability to create target devices emulators in the <strong>user space</strong>.</span></li>
 
-                                        <li><span>Due to reworked I/O architecture and SCST backend iSCSI-SCST has much
-                                         better performance in many cases and has potential for future improvements, like zero-copy 
-                                         with Linux cache FILEIO. In many tests iSCSI-SCST outperforms tuned for best
-                                         performance IET on more than 100%.</span></li>
-                               </ul>\r
+                                       <li><span>Ability to create <strong>multi-transport SCSI targets</strong>, which can export (possibly, the same) 
+                                       devices over multiple transports.</span></li>                                                                                                                            
+                               </ul>                                    
+                               
+                               <p>Also, due to reworked I/O architecture and SCST backend iSCSI-SCST has much
+                               better performance in many cases and has potential for future improvements, like zero-copy 
+                               with Linux cache FILEIO. In many tests iSCSI-SCST outperforms tuned for best
+                               performance IET on more than 100%.</p>
+                               
+                               <p>Advantages of iSCSI-SCST over IET are summarized on the <a href="comparison.html">Comparison</a> page.</p>
 
                                <p>If you are an IET user before installation carefully read README files of both iSCSI-SCST and 
                                the SCST core. Especially pay attention that now the LUN information for iSCSI-SCST is configured not using