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ISCSI-SCST updates

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git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@163 d57e44dd-8a1f-0410-8b47-8ef2f437770f
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Vladislav Bolkhovitin
2007-08-15 09:59:46 +00:00
parent e6a57baa14
commit 5d4789c8c0
1 changed files with 100 additions and 2 deletions
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@@ -201,6 +201,104 @@ enabling/disabling target mode on your target SCSI controller.<br>
<p><a
href="http://sourceforge.net/project/showfiles.php?group_id=110471">Download</a>
</p>
<hr
style="width: 100%; height: 2px; margin-left: 0px; margin-right: 0px;">
<h1><small>ISCSI target driver iSCSI-SCST<br>
</small></h1>
<div style="text-align: justify;">
<p>ISCSI-SCST is a forked (with all respects) version of <a
href="http://iscsitarget.sourceforge.net/">IET</a> with
updates to work over SCST as well as with many improvements and
bugfixes. The reason of fork is that the necessary changes are
intrusive and with the current IET 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 IET
trunk.<br>
</p>
<p>ISCSI-SCST has the following major advantages over the mainline IET:<br>
</p>
<ul>
<li>It uses full SCST power without loosing any existing feature
(except, maybe, "illegal" from SCSI specifications point of view MPIO).
Namely, you can use with it:</li>
</ul>
<ul style="list-style-type: circle; margin-left: 40px;">
<li>Pass-through mode with one to many relationship, i.e. when
multiple initiators can connect to the exported pass-through devices
(see above). For instance, you can safely export your parallel SCSI
tape or tape library on your iSCSI net and multiple initiators can
share it without risk of data loss because of the shared usage.
Existing "rawio" patch for IET supports only non-enforced 1:1
relationship, so it is unsafe to use it in multiple initiators
environments.<br>
</li>
<li>More advances devices visibility management, when different
initiators can see different set of devices with different access
permissions from the same target.</li>
<li>O_DIRECT, i.e. "BLOCKIO on files", 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.</li>
<li>With 4KB blocks you can forget about abysmal write performance
caused by misaligned partitions. All modern OS'es, including Windows
starting from, at least, Windows 2000, work perfectly with 4KB block
devices without any additional storage or handling overhead.</li>
<li>Virtual CD/DVD-ROMs without necessity for manual patching.</li>
<li>Ability to create target devices emulators in the user space.</li>
<li>Ability to create multi-transport SCSI targets, which can export
(possibly, the same) devices over multiple transports.</li>
</ul>
<ul>
<li>It has many code improvements and cleanups, including stability
and iSCSI RFC violations fixes. If you are an IET user and consider IET
problemless, I'm sorry for the bad news. IET works well only on "fast"
paths and regularly used branches, in many other less used cases IET
has various problems, from simply ignoring error processing, as it is
with memory allocations, to crashing itself with BUG() macro, as it is
for malformed packets from initiators. ChangeLog file lists most
noticeable fixes, but there were a lot of many other smaller ones.</li>
</ul>
<ul>
<li>Due to its reworked IO architecture and SCST backend iSCSI-SCST
has better performance in many cases. In future with upcoming SCST
improvements, like zero-copy with Linux cache FILEIO, the performance
difference is going to be even bigger. Currently in tests from a single
initiator over a single connection on 1GbE hardware over FILEIO vdisk
iSCSI-SCST with default settings usually outperforms tuned IET a on
3-10% (by default IET has not too good settings, so it shows
considerably worse results) or has the similar performance. The bigger
difference is expected with 10GbE hardware or with higher number of
initiators, since iSCSI-SCST has less commands processing overhead per
command, hence put less load on CPU. If you find a case where
iSCSI-SCST has worse performance, than IET, please report it to SCST
mailing list scst-devel@lists.sourceforge.net, it will be greatly
appreciated.</li>
</ul>
<p>Also, in contrast to IET, iSCSI-SCST is open for any new
development, modifications and improvements, so people who want to fix
or implement something new will not have to keep and maintain separate
patches as it is currently necessary with IET. ISCSI-SCST is going to
be actively developed and gain in the future new features like support
for multiple connections per session, error recovery levels &gt;0,
etc., which eventually make it really "enterprise".<br>
</p>
<p>ISCSI-SCST is available for download from the <a
href="http://svn.sourceforge.net/scst">SCST SVN repository</a>. See
above how to setup access to it.<br>
</p>
<p>After some testing for month-two, iSCSI-SCST is going to be fully
released.<br>
</p>
<p>If you are an IET user, please, 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 iscsi-scstd.conf file in /etc, but using corresponding SCST
facilities. This is because now the responsibilities are divided (as it
should be) between the target driver (iSCSI-SCST) and the SCST core.
The target driver is responsible for handling targets and their
parameters, SCST core is responsible for handling backstorage.<br>
</p>
</div>
<hr
style="width: 100%; height: 2px; margin-left: 0px; margin-right: 0px;">
<h1><small>Target driver for QLogic 2200/2300 cards<br>
@@ -231,7 +329,7 @@ to it.<br>
<h1><small>Target driver for LSI/MPT cards</small></h1>
Target driver LSI/MPT cards was originally developed by Hu Gang, then
Erik Habbinga has continued the development. This driver is on the
alpha stage and available from the <a
alpha stage and available for download from the <a
href="http://svn.sourceforge.net/scst">SCST SVN repository</a>. See
above how to setup access to it.<br>
<br>
@@ -257,7 +355,7 @@ One major difference of this driver from the above target driver for
QLogic 2200/2300 cards is that it supports 24xx series of chipsets.<br>
<br>
This driver is unstable and on the
alpha stage. It is available from the <a
alpha stage. It is available for download from the <a
href="http://svn.sourceforge.net/scst">SCST SVN repository</a>. See
above how to setup access to it.<br>
<br>