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Comparison between various SCSI targets for Linux added

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git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@750 d57e44dd-8a1f-0410-8b47-8ef2f437770f
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Vladislav Bolkhovitin
2009-04-04 18:48:12 +00:00
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<h1>Target Drivers</h1>
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<div id="main">
<h1>Features comparison between Linux SCSI targets</h1>
<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>
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&copy; Copyright 2008 <b><font color="#EC981F">Vladislav Bolkhovitin & others.</font>&nbsp;&nbsp;
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<h1>SCST vs STGT</h1>
<p><strong><a href="http://stgt.berlios.de/">STGT</a></strong> is alternative, independent from SCST implementation

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growing demand in a such subsystem. At the same time, SCST has reached
<strong>mature and stable </strong> state and <strong>capable to satisfy
</strong> all the requirements. See
<a href="scstvsstgt.html">SCST vs STGT</a> page for more details.</p>
<a href="comparison.html">Comparison</a> page for more details.</p>
<p>Also is has <strong>the widest choice</strong> of supported SCSI transports
(iSCSI, Fibre Channel, Infiniband SRP, parallel SCSI, SAS), <strong>the

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</div>

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www/target_qla_isp.html
View File

@@ -25,7 +25,7 @@
<li id="current"><a href="targets.html">Drivers</a></li>
<li><a href="downloads.html">Downloads</a></li>
<li><a href="contributing.html">Contributing</a></li>
<li><a href="scstvsstgt.html">SCST vs STGT</a></li>
<li><a href="comparison.html">Comparison</a></li>
</ul>
</div>

2
www/target_srp.html
View File

@@ -25,7 +25,7 @@
<li id="current"><a href="targets.html">Drivers</a></li>
<li><a href="downloads.html">Downloads</a></li>
<li><a href="contributing.html">Contributing</a></li>
<li><a href="scstvsstgt.html">SCST vs STGT</a></li>
<li><a href="comparison.html">Comparison</a></li>
</ul>
</div>

2
www/targets.html
View File

@@ -25,7 +25,7 @@
<li id="current"><a href="targets.html">Drivers</a></li>
<li><a href="downloads.html">Downloads</a></li>
<li><a href="contributing.html">Contributing</a></li>
<li><a href="scstvsstgt.html">SCST vs STGT</a></li>
<li><a href="comparison.html">Comparison</a></li>
</ul>
</div>