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git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@890 d57e44dd-8a1f-0410-8b47-8ef2f437770f
This commit is contained in:
Vladislav Bolkhovitin
2009-06-03 18:57:37 +00:00
parent 3fe62e70a8
commit b25f375dac
4 changed files with 42 additions and 41 deletions
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66
www/comparison.html
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@@ -43,7 +43,7 @@
<div id="main">
<h1>Features comparison between Linux SCSI targets</h1>
<p><small>As on April 2009</small></p>
<p><small>As on June 2009</small></p>
<table bgcolor="#F0F0F0" border="1" cols="5" cellspacing="1" cellpadding="7" style="text-align:center" width="620">
@@ -145,20 +145,22 @@ resized through AENs or Unit Attentions</th> <td> + </td> <td> - </td> <td>
<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 </td> <td> Not safe </td>
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>
</tr>
<th align="left"> Safe implementation of Task Management commands
<sup><A HREF="#13">13</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
<sup><A HREF="#14">14</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="#21">
21</A></sup></td> <td> -, <br/>data
<sup><A HREF="#15">
15</A></sup></td> <td> -, <br/>data
corruption possible
<sup><A HREF="#21">
21</A></sup> </td>
<sup><A HREF="#15">
15</A></sup> </td>
</tr>
<tr>
<th align="left"> Persistent Reservations <br/>
@@ -172,7 +174,7 @@ ORDERED commands</th> <td> + </td> <td> + </td> <td> -, <br/> data
</tr>
<tr>
<th align="left"> SCSI MIBs </th> <td> - </td> <td> - </td> <td> - </td> <td> -
<sup><A HREF="#15">15</A></sup></td>
<sup><A HREF="#16">16</A></sup></td>
</tr>
<tr>
<th align="left"> Cluster Storage Integration </th> <td> - </td> <td> - </td> <td> - </td> <td> VHACS </td>
@@ -226,14 +228,14 @@ ORDERED commands</th> <td> + </td> <td> + </td> <td> -, <br/> data
</tr>
<tr>
<th align="left"> SCSI pass-through
<sup><A HREF="#16">16</A></sup></th> <td> + </td> <td> - </td> <td> - </td> <td> Single initiator only, not enforced
<sup><A HREF="#17">17</A></sup></td>
<sup><A HREF="#17">17</A></sup></th> <td> + </td> <td> - </td> <td> - </td> <td> Single initiator only, not enforced
<sup><A HREF="#18">18</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="#18">18</A>
<A HREF="#19">19</A>
</sup></td> <td> - <sup>
<A HREF="#8">8</A>
</sup> </td> <td> BLOCKIO </td> <td> BLOCKIO, pass-
@@ -276,7 +278,7 @@ devices</th> <td> - </td> <td>Experimental</td> <td> - </td> <td> - </t
</tr>
<tr>
<th align="left"> Zero-copy data send/receive</th> <td> Send only<sup>
<A HREF="#19">19</A>
<A HREF="#20">20</A>
</sup> </td> <td> None <sup>
<A HREF="#8">8</A>
</sup> </td> <td> Send only</td> <td> Send only </td>
@@ -303,13 +305,13 @@ devices</th> <td> - </td> <td>Experimental</td> <td> - </td> <td> - </t
(AEN) </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
</tr>
<th align="left"> Safe implementation of connections and sessions
reinstatement <sup><A HREF="#20">20</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
reinstatement <sup><A HREF="#21">21</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="#21">21</A></sup></th> <td> Safe </td> <td> ? </td> <td> Not safe </td> <td> ?</td>
<th align="left"> Safe restart <sup><A HREF="#22">22</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="#15">15</A></sup></td>
<sup><A HREF="#16">16</A></sup></td>
</tr>
</table>
@@ -322,9 +324,8 @@ reinstatement <sup><A HREF="#20">20</A></sup></th> <td> Safe </td> <td> Not s
<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. ISER target driver has long known (since Feb 2008) data corruption problem, which localization hasn't been determined yet and might be
in the STGT core. See <a href="http://lists.berlios.de/pipermail/stgt-devel/2008-February/001367.html">
http://lists.berlios.de/pipermail/stgt-devel/2008-February/001367.html</a> and
<a href="http://lists.wpkg.org/pipermail/stgt/2009-February/002630.html">http://lists.wpkg.org/pipermail/stgt/2009-February/002630.html</a>.</p>
in the STGT core. See <a href="http://lists.berlios.de/pipermail/stgt-devel/2008-February/001367.html">here</a> and
<a href="http://lists.wpkg.org/pipermail/stgt/2009-February/002630.html">here</a>.</p>
<p><A NAME="4"></A> 4. The result "in average" is listed. One target can be better somewhere, another one somewhere else. Although manual tuning of target and
system parameters tends the restore the difference listed in the comparison. You can find example measurements <a href="vl_res.txt">here</a>,
@@ -362,7 +363,11 @@ reinstatement <sup><A HREF="#20">20</A></sup></th> <td> Safe </td> <td> Not s
<a href="http://communities.vmware.com/thread/53797?tstart=0&start=15">"Russian roulette with your data"</a> on the VMware
community forum by someone working for VMware.</p>
<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
<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
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
@@ -372,35 +377,34 @@ reinstatement <sup><A HREF="#20">20</A></sup></th> <td> Safe </td> <td> Not s
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="14"></A> 14. Both IET and LIO report in INQUIRY command response support for full task management model. But they process ORDERED
<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
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="15"></A> 15. The IETF SCSI-MIB (RFC 4455) is not supported by LIO, only proprietary MIBs SBE-SCSI-MIB, SBE-ISCSI-MIB and SBE-IPS-AUTH-MIB are supported.</p>
<p><A NAME="16"></A> 16. The IETF SCSI-MIB (RFC 4455) is not supported by LIO, only proprietary MIBs SBE-SCSI-MIB, SBE-ISCSI-MIB and SBE-IPS-AUTH-MIB are supported.</p>
<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
<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
SCSI tape or SATA DVD-RW device to your iSCSI network.</p>
<p><A NAME="17"></A> 17. LIO doesn't emulate all the necessary SCSI host functionality to allow to share SCSI devices
<p><A NAME="18"></A> 18. LIO doesn't emulate all the necessary SCSI host functionality to allow to share SCSI devices
in pass-through mode to several initiators. It 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 LIO doesn't issue no warning about it, so you can quietly corrupt your data.
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>
isn't enforced anyhow and LIO doesn't issue no warning about it, so an user will not be notified about it
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="18"></A> 18. You can find proposal how to implement zero-copy FILEIO in SCST on the <a href="contributing.html#ZC_READ">
<p><A NAME="19"></A> 19. 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="19"></A> 19. Doesn't need any kernel patch, except in case, when used with user space backend.</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="20"></A> 20. Connections and sessions reinstatement is, basically, a kind of Task Management command, because it implies commands aborting.
<p><A NAME="21"></A> 21. 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="21"></A> 21. "Safe restart" means that after the iSCSI target restart, all the connected initiators will seamlessly restore all existing before
<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
the restart connections. "Not safe" means that, most likely, the connected initiators will fail to restore
existing connections with some errors.</p>

8
www/mc_s.html
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@@ -173,7 +173,7 @@ commands get executed, although it would be better for performance to
reorder them. As result, MPIO sometimes has better performance, than
MC/S, especially in setups, where maximum IOPS number is important. See,
for instance,
<a href="http://article.gmane.org/gmane.linux.scsi/16311">http://article.gmane.org/gmane.linux.scsi/16311</a>.
<a href="http://article.gmane.org/gmane.linux.scsi/16311">here</a>.
</p>
<h2>When MC/S is better than MPIO</h2>
@@ -232,10 +232,8 @@ and backup applications one or both can be true. But on practice:</p>
<p> Simply, MC/S is done on the wrong level. No surprise then that no
Open Source OS'es neither support, nor going to implement it. Moreover,
when back to 2005 there was an attempt to add MC/S in Linux, it was
rejected. See for more details <a
href="http://article.gmane.org/gmane.linux.scsi/15769">http://article.gmane.org/gmane.linux.scsi/15769</a>
and <a
href="http://article.gmane.org/gmane.linux.scsi/16301">http://article.gmane.org/gmane.linux.scsi/16301</a>.
rejected. See for more details <a href="http://article.gmane.org/gmane.linux.scsi/15769">here</a>
and <a href="http://article.gmane.org/gmane.linux.scsi/16301">here</a>.
</p>
<p>If in future SCSI standards gain possibility to group several I_T nexuses

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@@ -49,8 +49,8 @@
found its way to the kernel.</p>
<p>But such architecture has several inherent problems. Among them performance and complexity.
See description for the set of patches, submitted for the first iteration of in-kernel inclusion review and comments
<a href="http://lkml.org/lkml/2008/12/10/245">http://lkml.org/lkml/2008/12/10/245</a></p>
See <a href="http://lkml.org/lkml/2008/12/10/245">description</a> for the set of patches, submitted for
the first iteration of in-kernel inclusion review and comments in Linux kernel mailing list.</p>
<p>See also the following important discussions:
<ul>
@@ -63,8 +63,7 @@
<li><span><a href="http://news.gmane.org/find-root.php?message_id=%3c43987F75.2000301%40vlnb.net%3e">
"Stgt a new version of iscsi target?"</a>, especially pay attention to
this message: <a href="http://article.gmane.org/gmane.linux.scsi/21073">
http://article.gmane.org/gmane.linux.scsi/21073</a> why STGT's architecture was considered "right".
<a href="http://article.gmane.org/gmane.linux.scsi/21073">this</a> message why STGT's architecture was considered "right".
</span></li>
</ul></p>

2
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@@ -54,7 +54,7 @@
<div id="main">
<h1>Target driver for QLogic 22xx/23xx cards</h1>
<p><img src="images/t_qlogic.gif" width="100" height="120" class="float-left" />
This is target driver for QLogic 22xx/23xx Fibre Channel cards. It is stable and well tested.</p>
This is target driver for QLogic 22xx/23xx (qla2200/qla2300) Fibre Channel cards. It is stable and well tested.</p>
<p>The latest stable version is 1.0.1. Requires Linux kernel version 2.6.16.x or higher and
SCST version 1.0.1 or higher.</p>