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    SubjectIntegration of SCST in the mainstream Linux kernel
    As you probably know there is a trend in enterprise computing towards
    networked storage. This is illustrated by the emergence during the
    past few years of standards like SRP (SCSI RDMA Protocol), iSCSI
    (Internet SCSI) and iSER (iSCSI Extensions for RDMA). Two different
    pieces of software are necessary to make networked storage possible:
    initiator software and target software. As far as I know there exist
    three different SCSI target implementations for Linux:
    - The iSCSI Enterprise Target Daemon (IETD,
    http://iscsitarget.sourceforge.net/);
    - The Linux SCSI Target Framework (STGT, http://stgt.berlios.de/);
    - The Generic SCSI Target Middle Level for Linux project (SCST,
    http://scst.sourceforge.net/).
    Since I was wondering which SCSI target software would be best suited
    for an InfiniBand network, I started evaluating the STGT and SCST SCSI
    target implementations. Apparently the performance difference between
    STGT and SCST is small on 100 Mbit/s and 1 Gbit/s Ethernet networks,
    but the SCST target software outperforms the STGT software on an
    InfiniBand network. See also the following thread for the details:
    http://sourceforge.net/mailarchive/forum.php?thread_name=e2e108260801170127w2937b2afg9bef324efa945e43%40mail.gmail.com&forum_name=scst-devel.

    About the design of the SCST software: while one of the goals of the
    STGT project was to keep the in-kernel code minimal, the SCST project
    implements the whole SCSI target in kernel space. SCST is implemented
    as a set of new kernel modules, only minimal changes to the existing
    kernel are necessary before the SCST kernel modules can be used. This
    is the same approach that will be followed in the very near future in
    the OpenSolaris kernel (see also
    http://opensolaris.org/os/project/comstar/). More information about
    the design of SCST can be found here:
    http://scst.sourceforge.net/doc/scst_pg.html.

    My impression is that both the STGT and SCST projects are well
    designed, well maintained and have a considerable user base. According
    to the SCST maintainer (Vladislav Bolkhovitin), SCST is superior to
    STGT with respect to features, performance, maturity, stability, and
    number of existing target drivers. Unfortunately the SCST kernel code
    lives outside the kernel tree, which makes SCST harder to use than
    STGT.

    As an SCST user, I would like to see the SCST kernel code integrated
    in the mainstream kernel because of its excellent performance on an
    InfiniBand network. Since the SCST project comprises about 14 KLOC,
    reviewing the SCST code will take considerable time. Who will do this
    reviewing work ? And with regard to the comments made by the
    reviewers: Vladislav, do you have the time to carry out the
    modifications requested by the reviewers ? I expect a.o. that
    reviewers will ask to move SCST's configuration pseudofiles from
    procfs to sysfs.

    Bart Van Assche.


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