[zeuux-linux] Fwd: [ANNOUNCE]: ISCSI target driver iSCSI-SCST released

[WANG Cong]

----- Forwarded message from Vladislav Bolkhovitin <> -----

From: Vladislav Bolkhovitin <>
Date: Tue, 08 Jul 2008 23:17:58 +0400
User-Agent: Thunderbird 2.0.0.9 (X11/20071115)
To: linux-kernel at vger.kernel.org, linux-scsi at vger.kernel.org
CC: scst-devel <scst-devel at lists.sourceforge.net>
Subject: [ANNOUNCE]: ISCSI target driver iSCSI-SCST released

I'm glad to announce that version 1.0.0 of iSCSI target driver iSCSI-SCST 
released and available for download from  
http://scst.sourceforge.net/downloads.html.

ISCSI-SCST is a forked (with all respects) version of IET with updates to 
work in SCST environment (http://scst.sourceforge.net) as well as with many 
improvements and bugfixes. ISCSI-SCST has the following major advantages 
over the mainline IET:

* It uses full power of SCST without loosing existing features. Namely, you 
can additionally use with it:

          o Pass-through mode with one to many relationship, i.e. when
            multiple initiators can connect to the exported pass-through
            devices.

          o More advances devices visibility management, when different
            initiators can see different set of devices with different
            access permissions from the same target.

          o 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.

          o With 4KB blocks you can forget about abysmal write
            performance caused by misaligned partitions.

          o Virtual CD/DVD-ROMs without necessity for manual patching.

          o Ability to create target devices emulators in the user
            space.

          o 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. Many IET users use it for ages without problems, so 
they consider it problemless. But, in fact, unfortunately, it isn't so. 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, and crashing itself with 
BUG() macro, as it is for malformed packets from initiators, to possible 
data corruption.

* Due to reworked I/O architecture and SCST backend iSCSI-SCST has better 
performance in many cases. In future with upcoming improvements in SCST 
core, like zero-copy with Linux cache, 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 for best performance IET a on 3-30%. The 
difference is especially noticeably with real storage, not NULLIO or RAM 
disks. On 10GbE hardware the performance difference is often as high as 
100-200% or even more. With higher number of initiators the difference will 
be even bigger. This is because iSCSI-SCST has less commands processing 
overhead per command, hence has smaller processing latency and puts less 
load on CPU.

Detail description of iSCSI-SCST you can find on its page
http://scst.sourceforge.net/target_iscsi.html.

This driver is being prepared in form of patch for review and
inclusion into the kernel.

Vlad

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