+
ISCSI-SCST is a forked (with all respects) version of IET 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.
+
+
ISCSI-SCST has the following major advantages over the mainline IET:
+
+
+ - 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:
+
+
+ - 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.
+
+ - More advances devices visibility management, when different
+initiators can see different set of devices with different access
+permissions from the same target.
+ - 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.
+ - 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.
+ - Virtual CD/DVD-ROMs without necessity for manual patching.
+ - Ability to create target devices emulators in the user space.
+ - Ability to create multi-transport SCSI targets, which can export
+(possibly, the same) devices over multiple transports.
+
+
+ - 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.
+
+
+ - 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.
+
+
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 >0,
+etc., which eventually make it really "enterprise".
+
+
ISCSI-SCST is available for download from the SCST SVN repository. See
+above how to setup access to it.
+
+
After some testing for month-two, iSCSI-SCST is going to be fully
+released.
+
+
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.
+
+