Re: Integration of SCST in the mainstream Linux kernel

Vladislav Bolkhovitin
2008-01-23T17:38:44Z

Bart Van Assche wrote:
> 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.

Sure, I do, although I personally don't see much sense in such move.

> Bart Van Assche.
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