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+<title>SCST: Generic SCSI Target Middle Level for Linux</title>\r
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+ <div class="logoimg"></div><h1 id="logo"><span class="orange"></span></h1>\r
+ <h2 id="slogan">SCSI Target Middle Level for Linux</h2> \r
+ </div> \r
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+ <ul>\r
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+ <h1>Target Drivers</h1>\r
+ <ul class="sidemenu">
+ <li><a href="comparison.html">Features comparison</a></li>
+ <li><a href="scstvsstgt.html">SCST vs STGT</a></li>
+ </ul>
+ </div> \r
+
+ <div id="main">
+ <h1>Features comparison between Linux SCSI targets</h1>\r
+
+ <p><small>As on April 2009</small></p>
+
+<table bgcolor="#F0F0F0" border="1" cols="5" cellspacing="1" cellpadding="7" style="text-align:center" width="620">
+
+<tr>
+<th>
+</th><th> <a href="http://scst.sourceforge.net/" title="http://scst.sourceforge.net/" rel="nofollow">SCST</a>
+</th><th> <a href="http://stgt.berlios.de/" title="http://stgt.berlios.de/" rel="nofollow">STGT</a>
+</th><th> <a href="http://iscsitarget.sourceforge.net/" title="http://iscsitarget.sourceforge.net/" rel="nofollow">IET</a>
+</th><th> <a href="http://linux-iscsi.org/" title="http://linux-iscsi.org/" rel="nofollow">LIO v3.0</a>
+</th></tr>
+
+<tr bgcolor="#E0E0E0">
+<td colspan="5"> <b>General</b>
+</td></tr>
+<tr>
+<th align="left"> Upstream kernel</th> <td> - </td> <td> Kernel part </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Generic Target Engine </th> <td> + </td> <td> + </td> <td> iSCSI only </td> <td> Under development </td>
+</tr>
+<tr>
+<th align="left"> Architecture </th> <td> Kernel only</td> <td> User space only
+ <sup><A HREF="#1">1</A>
+ </sup> </td> <td> Split <sup>
+ <A HREF="#2">2</A>
+ </sup> </td> <td> Kernel only </td>
+</tr>
+<tr>
+<th align="left"> Stability </th> <td> + </td> <td> + </td> <td> + </td> <td> Heavy development </td>
+</tr>
+<tr>
+<th align="left"> Performance </th> <td> ***** </td> <td> ***</td> <td> **** </td> <td> ****
+ <sup><A HREF="#3">3</A></sup></td>
+</tr>
+<tr>
+<th align="left"> Zero-Copy </th> <td> **** </td> <td> ***
+ <sup><A HREF="#4">4</A>
+ </sup> </td> <td> **** </td> <td> **** </td>
+</tr>
+<tr>
+<th align="left"> Support for transports without expecting
+transfer values (parallel SCSI, SAS) </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> User Interface </th> <td> ProcFS </td> <td> Custom </td> <td> IOCTL/ProcFS </td> <td> ConfigFS/IOCTL </td>
+</tr>
+
+
+<tr bgcolor="#E0E0E0">
+<td colspan="5"> <b>Major features</b>
+</td></tr>
+<tr>
+<th align="left"> Target drivers in kernel space </th> <td> + </td> <td> + </td> <td> - </td> <td> Under development </td>
+</tr>
+<tr>
+<th align="left"> Target drivers in user space </th> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Backstorage handlers in kernel space </th> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
+</tr>
+<tr>
+<th align="left"> Backstorage handlers in user space </th> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Local access to emulated backstorage devices</th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Advanced devices visibility management </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Support for Asynchronous Event Notifications
+(AEN) </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> AEN for devices added/removed</th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> AEN for devices resized</th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Bidirectional Commands </th> <td> + <sup>
+ <A HREF="#5">5</A>
+ </sup></td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Extended CDB (size >16 bytes) </th> <td> + <sup>
+ <A HREF="#5">5</A>
+ </sup></td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Descriptor sense support </th> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<th align="left"> RESERVE/RELEASE
+<small> (Windows 2003 clustering) </small></th> <td> + </td> <td> + </td> <td> + </td> <td> + </td>
+</tr>
+<th align="left"> Safe RESERVE/RELEASE implementation according to
+SCSI requirements <sup><A HREF="#6">6</A></sup></th> <td> Safe </td> <td> Safe </td> <td> Not safe </td> <td> Not safe </td>
+</tr>
+<th align="left"> Safe implementation of Task Management commands
+<sup><A HREF="#7">7</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
+</tr>
+<tr>
+<th align="left"> Persistent Reservations <br/>
+<small> (Windows 2008 clustering)</small></th> <td> - </td> <td> - </td> <td> - </td> <td> Under development </td>
+</tr>
+<tr>
+<th align="left"> ALUA </th> <td> - </td> <td> - </td> <td> - </td> <td> Under development </td>
+</tr>
+<tr>
+<th align="left"> Failover Clustering </th> <td> + </td> <td> ? </td> <td> + </td> <td> + </td>
+</tr>
+<tr>
+<th align="left"> SCSI MIBs </th> <td> - </td> <td> - </td> <td> - </td> <td> + </td>
+</tr>
+<tr>
+<th align="left"> Cluster Storage Integration </th> <td> - </td> <td> - </td> <td> - </td> <td> VHACS </td>
+</tr>
+
+
+<tr bgcolor="#E0E0E0">
+<td colspan="5"> <b>Supported SCSI transports</b>
+</td></tr>
+<tr>
+<th align="left"> iSCSI </th> <td> + </td> <td> + </td> <td> + </td> <td> + </td>
+</tr>
+<tr>
+<th align="left"> Fibre Channel </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> SRP </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> iSER </th> <td> - </td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Parallel (Wide) SCSI </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> SAS </th> <td> Under
+ development </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> FCoE </th> <td> Under
+ development </td> <td>Under
+ development</<td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> IBM pSeries Virtual SCSI </th> <td> - </td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+
+<tr bgcolor="#E0E0E0">
+<td colspan="5"> <b>Supported backstorage</b>
+</td></tr>
+<tr>
+<th align="left"> Kernel side FILEIO </th> <td> + </td> <td> - </td> <td> + </td> <td> + </td>
+</tr>
+<tr>
+<th align="left"> Kernel side BLOCKIO </th> <td> + </td> <td> - </td> <td> + </td> <td> + </td>
+</tr>
+<tr>
+<th align="left"> User space side FILEIO </th> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> SCSI Pass-through </th> <td> + </td> <td> - </td> <td> - </td> <td> Single initiator only, not enforced
+ <sup><A HREF="#8">8</A></sup></td>
+</tr>
+<tr>
+<th align="left"> 4k sectors support in pass-through mode </th> <td> + </td> <td> - </td> <td> - </td> <td> ? </td>
+</tr>
+<tr>
+<th align="left"> 4k, 2k, 1k and 512 byte sectors emulation
+in modes, other than pass-through </th> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
+</tr>
+<tr>
+<th align="left"> CDROM emulation from ISO files </th> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+
+<tr bgcolor="#E0E0E0">
+<td colspan="5"> <b>iSCSI Target</b>
+</td></tr>
+<tr>
+<th align="left"> Architecture </th> <td> Split <sup>
+ <A HREF="#2">2</A>
+ </sup> </td> <td> User space
+ only </td> <td> Split <sup>
+ <A HREF="#2">2</A>
+ </sup></td> <td> Kernel only </td>
+</tr>
+<tr>
+<th align="left"> MC/S </th> <td> - </td> <td> - </td> <td> - </td> <td> + </td>
+</tr>
+<tr>
+<th align="left"> Max ErrorRecoveryLevel </th> <td> 0 </td> <td> 0 </td> <td> 0 </td> <td> 2 </td>
+</tr>
+<tr>
+<th align="left"> Bidirectional Commands </th> <td> + <sup>
+ <A HREF="#5">5</A>
+ </sup></td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Extended CDB (size >16 bytes) </th> <td> + <sup>
+ <A HREF="#5">5</A>
+ </sup></td> <td> + </td> <td> - </td> <td> - </td>
+</tr>
+<tr>
+<th align="left"> Support for Asynchronous Event Notifications
+(AEN) </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
+</tr>
+<th align="left"> Safe implementation of connections and sessions
+reinstatement <sup><A HREF="#9">9</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
+</tr>
+<tr>
+<th align="left"> iSCSI MIBs </th> <td> - </td> <td> - </td> <td> - </td> <td> -
+ <sup><A HREF="#10">10</A></sup></td>
+</tr>
+</table>
+
+<br/>
+<p><strong><big><u>REMARKS:</u></big></strong></p>
+
+<p><A NAME="1"></A> 1. STGT has SCSI target engine in user space and small hooks in the kernel to interact with in-kernel target drivers.</p>
+
+<p><A NAME="2"></A> 2. All iSCSI management implemented in user space and actual data transfers in kernel space without user space involved.</p>
+
+<p><A NAME="3"></A> 3. The conclusion made by source code study only. LIO should have performance
+ on the IET level or slightly less, because of more processing overhead. </p>
+
+<p><A NAME="4"></A> 4. Some zero-copy functionality isn't available from user space. For instance, zero-copy send to a socket.</p>
+
+<p><A NAME="5"></A> 5. Not well tested, because at the moment there is no backend using this functionality.</p>
+
+<p><A NAME="6"></A> 6. SCSI requires that if an initiator clears reservation held by another initiator, the reservation holder must be notified
+ about the reservation clearance. Otherwise, several initiators can at the same time change supposed to be protected by the
+ reservation data, which can corrupt them.</p>
+
+<p><A NAME="7"></A> 7. After a task management command completed and corresponding response was sent to initiator, who sent that task management
+ command, all the affected SCSI commands must get into a state, where they can't affect following after
+ the tasks management response commands from this initiator. This is the safe implementation.
+ The unsafe implementation only marks all the affected
+ SCSI commands as aborted and then immediately send task management response to the initiator. This implementation only
+ guarantees that the initiator will never receive responses from those commands, but it doesn't
+ guarantee that none of those commands will get executed by backstorage <strong>*AFTER*</strong> any
+ SCSI command, which initiator will send after it received the task management response thinking
+ that all the aborted commands actually fully aborted. This could lead to a data corruption.</p>
+
+<p><A NAME="8"></A> 8. LIO doesn't emulate all the necessary SCSI host functionality to allow to share a SCSI device
+ in pass-through mode to several initiators. It can only pass SCSI commands from initiator to
+ the SCSI device. This is safe only if there is only one initiator. This limitation
+ isn't enforced anyhow by LIO. You can find more technical information about that in
+ <a href="http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html">
+ http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html</a></p>
+
+<p><A NAME="5"></A> 9. Connections and sessions reinstatement is, basically, a kind of Task Management command.
+ For instance, open-iscsi uses it as such in eh_target_reset_handler() callback. So, similarly
+ to <A HREF="#7">(7)</A> above, a safe implementation
+ must not accept SCSI commands from new connection/session until all the SCSI commands in
+ being reinstated connection/session get into a state, where they can't affect the new commands.</p>
+
+<p><A NAME="10"></A> 10. SCSI-MIB (RFC 4455) - not supported;
+ SBE-SCSI-MIB - supported by LIO v2.6, not supported by LIO v3.0;
+ SBE-ISCSI-MIB - supported by LIO v2.6, not supported by LIO v3.0;
+ SBE-IPS-AUTH-MIB - supported by LIO v2.6, not supported by LIO v3.0
+
+</p>
+
+<br/>
+<hr style="width: 100%; height: 1px; margin-left: 15px; margin-right: 0px;">
+<br/>
+
+<p><strong>P.S.</strong> LIO has similar comparison
+<a href="http://www.linux-iscsi.org/index.php/Overview_Page">page</a>. It is very much
+wrong about SCST. I asked that page author, Nicholas Bellinger, to
+correct the wrong items (see <a href="http://sourceforge.net/mailarchive/forum.php?thread_name=49AECE0B.5030009%40vlnb.net&forum_name=scst-devel">my e-mail</a>),
+but Nicholas Bellinger refused to do it. Moreover, he blocked my access
+to the LIO mailing list, preventing me from tell that to the interested
+people myself. After all our previous discussions and with his skills
+and experience I can't believe that Nicholas Bellinger doesn't know that
+SCST is a lot more generic than LIO and has zero-copy in all the same
+places, where LIO has. So, that comparison page looks like rather a
+deliberate cheating attempt. Definitely, SCST in all major
+technical areas is so much superior over LIO, so Nicholas Bellinger started
+attacking people's perception about SCST trying to inspire them the
+opposite.</strong></p>
+
+ </div> \r
+ </div>\r
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+ © Copyright 2008 <b><font color="#EC981F">Vladislav Bolkhovitin & others.</font> \r
+ Design by: <b><font color="#EC981F">Daniel Fernandes</font></b> \r
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