<div id="main">
<h1>Features comparison between Linux SCSI targets</h1>\r
- <p><small>As on August 2009</small></p>
+ <p><small>As on October 2009</small></p>
<table bgcolor="#F0F0F0" border="1" cols="5" cellspacing="1" cellpadding="7" style="text-align:center" width="620">
<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="#12">12</A></sup></th> <td> Safe </td> <td> Safe </td> <td> Not safe
- <sup><A HREF="#13">
- 13</A></sup> </td> <td> Not safe </td>
+SCSI requirements <sup><A HREF="#12">12</A></sup></th> <td> Safe </td> <td> Safe </td> <td> Safe from
+ v1.4.18</td> <td> Not safe </td>
</tr>
<th align="left"> Safe implementation of Task Management commands
-<sup><A HREF="#14">14</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
+<sup><A HREF="#13">13</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
</tr>
<tr>
<th align="left"> Support for SCSI task attributes, including
ORDERED commands</th> <td> + </td> <td> + </td> <td> -, <br/> data
corruption possible
- <sup><A HREF="#15">
- 15</A></sup></td> <td> -, <br/>data
+ <sup><A HREF="#14">
+ 14</A></sup></td> <td> -, <br/>data
corruption possible
- <sup><A HREF="#15">
- 15</A></sup> </td>
+ <sup><A HREF="#14">
+ 14</A></sup> </td>
</tr>
<tr>
<th align="left"> Persistent Reservations <br/>
</tr>
<tr>
<th align="left"> SCSI MIBs </th> <td> - </td> <td> - </td> <td> - </td> <td> +-
- <sup><A HREF="#16">16</A></sup></td>
+ <sup><A HREF="#15">15</A></sup></td>
</tr>
<tr>
<th align="left"> Cluster Storage Integration </th> <td> - </td> <td> - </td> <td> - </td> <td> VHACS </td>
</tr>
<tr>
<th align="left"> SCSI pass-through
- <sup><A HREF="#17">17</A></sup></th> <td> + </td> <td> Disks only, single
+ <sup><A HREF="#16">16</A></sup></th> <td> + </td> <td> Disks only, single
initiator only, not
enforced <sup>
- <A HREF="#18">18</A>
+ <A HREF="#17">17</A>
</sup> </td> <td> - </td> <td> Single initiator only, not enforced
- <sup><A HREF="#18">18</A></sup></td>
+ <sup><A HREF="#17">17</A></sup></td>
</tr>
<tr>
<th align="left"> Zero-copy data read/write to/from backstorage</th> <td>BLOCKIO, user space
FILEIO in O_DIRECT mode,
pass-through <sup>
- <A HREF="#19">19</A>
+ <A HREF="#18">18</A>
</sup></td> <td> - <sup>
<A HREF="#8">8</A>
</sup> </td> <td> BLOCKIO </td> <td> BLOCKIO, pass-
</tr>
<tr>
<th align="left"> Zero-copy data send/receive</th> <td> Send only<sup>
- <A HREF="#20">20</A>
+ <A HREF="#19">19</A>
</sup> </td> <td> None <sup>
<A HREF="#8">8</A>
</sup> </td> <td> Send only</td> <td> Send only </td>
(AEN) </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
</tr>
<th align="left"> Safe implementation of connections and sessions
-reinstatement <sup><A HREF="#21">21</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
+reinstatement <sup><A HREF="#20">20</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
</tr>
-<th align="left"> Safe restart <sup><A HREF="#22">22</A></sup></th> <td> Safe </td> <td> ? </td> <td> Not safe </td> <td> ?</td>
+<th align="left"> Safe restart <sup><A HREF="#21">21</A></sup></th> <td> Safe </td> <td> ? </td> <td> Not safe </td> <td> ?</td>
</tr>
<tr>
<th align="left"> iSCSI MIBs </th> <td> - </td> <td> - </td> <td> - </td> <td> +-
- <sup><A HREF="#16">16</A></sup></td>
+ <sup><A HREF="#15">15</A></sup></td>
</tr>
</table>
community forum by someone working for VMware. But, sure, it can affect not only VMware, but also any other cluster
implementation, relying on this functionality.</p>
-<p><A NAME="13"></A> 13. The problem in IET
- <a href="http://sourceforge.net/mailarchive/message.php?msg_name=1239130617.11478.1282.camel%40blackadder">
- was confirmed</a> in IET mailing list.</p>
-
-<p><A NAME="14"></A> 14. After a task management command completed and before the corresponding response was sent to the initiator, who sent that task management
+<p><A NAME="13"></A> 13. After a task management command completed and before the corresponding response was sent to the 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 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="15"></A> 15. Both IET and LIO report in INQUIRY command response support for full task management model. But they process ORDERED
+<p><A NAME="14"></A> 14. Both IET and LIO report in INQUIRY command response support for full task management model. But they process ORDERED
commands the same way as SIMPLE commands, i.e. allow free reorder of them before they get executed. That violates SCSI standard
and can lead to a data corruption to any application relying on commands order provided by ORDERED attribute.</p>
-<p><A NAME="16"></A> 16. LIO exports the information needed for an RFC 4455 implementation, but requires additional RFC 4455 implementing module.
+<p><A NAME="15"></A> 15. LIO exports the information needed for an RFC 4455 implementation, but requires additional RFC 4455 implementing module.
At the moment, there is no open source implementation of such module.</p>
-<p><A NAME="17"></A> 17. SCSI pass-through mode allows to export your local SCSI-capable device. For instance with it you can share your parallel
+<p><A NAME="16"></A> 16. SCSI pass-through mode allows to export your local SCSI-capable device. For instance with it you can share your parallel
SCSI tape or SATA DVD-RW device to your iSCSI network.</p>
-<p><A NAME="18"></A> 18. STGT and LIO don't emulate all the necessary SCSI host functionality to allow to share SCSI devices
+<p><A NAME="17"></A> 17. STGT and LIO don't emulate all the necessary SCSI host functionality to allow to share SCSI devices
in pass-through mode to several initiators. They can only pass SCSI commands from initiators to
SCSI devices and responses back. This is safe only with a single initiator. This limitation
isn't enforced anyhow and both STGT and LIO don't issue any warning about it, so an user will not be notified about this
limitation and can quietly corrupt his/her data. You can find more technical information about it
<a href="http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html">here</a>.</p>
-<p><A NAME="1
9"></A> 19. You can find a proposal how to implement zero-copy FILEIO in SCST on the <a href="contributing.html#ZC_READ">
+<p><A NAME="1
8"></A> 18. You can find a proposal how to implement zero-copy FILEIO in SCST on the <a href="contributing.html#ZC_READ">
Contributing</a> page.</p>
-<p><A NAME="20"></A> 20. Doesn't need any kernel patch, except in the case, when used with user space backend.</p>
+<p><A NAME="19"></A> 19. Doesn't need any kernel patch, except in the case, when used with user space backend.</p>
-<p><A NAME="21"></A> 21. Connections and sessions reinstatement is, basically, a kind of Task Management command, because it implies commands aborting.
+<p><A NAME="20"></A> 20. Connections and sessions reinstatement is, basically, a kind of Task Management command, because it implies commands aborting.
For instance, open-iscsi uses it as a less intrusive substistute for target reset in eh_target_reset_handler() callback. So, similarly
to the safe task management above, a safe implementation of connections and sessions reinstatement
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 new commands.</p>
-<p><A NAME="22"></A> 22. "Safe restart" means that after the iSCSI target restart, all the connected initiators will seamlessly restore all existing before
+<p><A NAME="21"></A> 21. "Safe restart" means that after the iSCSI target restart, all the connected initiators will seamlessly restore all existing before
the restart connections. "Not safe" means that, most likely, the connected initiators will fail to restore
existing connections with some errors. However, your iSCSI initiator also should be able to handle the safe restart. For instance,
old (pre-CentOS/RHEL 5) open-iscsi has problems in this area. But the latest versions do it pretty well.</p>
</span></li>
- <li><span>ISCSI-SCST has many code improvements and cleanups, including <strong>stability</strong>
- and <strong>iSCSI RFC violations fixes</strong>.
+ <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
- corruption. See, for instance, <a href="http://communities.vmware.com/thread/53797?tstart=0&start=15">this</a>
- thread on a VMware forum about in which <strong>Russian roulette</strong> IET users play using it with VMware.</span></li>
+ corruptions, because of, for instance, unsafe task management or sessions reinstatement implementations.</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 <strong>zero-copy
- with Linux cache FILEIO</strong>. In many tests iSCSI-SCST outperforms tuned for best
- performance IET on <strong>more than 100%</strong>.
+ 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%.
</ul></p>\r
<p>If you are an IET user before installation carefully read README files of both iSCSI-SCST and
http://git.etherboot.org / mirror / scst / .git / commitdiff