Bug#808041: s390-zfcp: Install Debian on FC-attached SCSI devices on s390

[Hendrik Brueckner <brueckner@linux.vnet.ibm.com>]

Hi Dimitri,

On Tue, Dec 15, 2015 at 07:33:56PM +0000, Dimitri John Ledkov wrote:
> On 15 December 2015 at 17:07, Cyril Brulebois <kibi@debian.org> wrote:
> > Hendrik Brueckner <brueckner@linux.vnet.ibm.com> (2015-12-15):
> >> Package: d-i.debian.org
> >> Severity: normal
> >> Tags: d-i
> >>
> >> Dear Debian Installer Team and Maintainers,
> >>
> >> I would like to contribute a new package for the Debian Installer
> >> to configure FCP devices and install Debian on SCSI devices which
> >> are available on Linux on z Systems.
> >>
> >> FCP device provide access to SAN storage, for example, SCSI devices.
> >> SCSI devices and DASD devices are the main storage devices on a mainframe.
> >>
> >> With the FCP configuration utility, users can enable FCP devices.
> >> Depending on the hardware configuration of the FCP devices, LUNs will
> >> be automatically detected and attached;  alternatively, users are guided
> >> to manually add LUNs.  The FCP configuration utility can be preseeded
> >> to perform an unattended configuration of FCP devices.
> >>
> >> I will attach the patches for this new utility, as well as, a README
> >> with more details in another mail.
> >>
> >> Feedback for the FCP configuration utility is very welcome!
> >> I am looking forward to discuss and work with you on the steps to make
> >> it available with the Debian Installer.
> >
> > Thanks! I'm adding Philipp and S/390 people in copy so that we get as
> > many eyes as possible on your proposed patches. I'm afraid I don't know
> > much about this platform for one thing, and lack time to learn more
> > about it right now for another; sorry about that. :/
> 
> 
> I'm part of debian-installer team, and have been mostly uploading
> partman-* et.al. packages. So I don't know all of the d-i, but do have
> a fairly good working knowledge of it. I certainly can review /
> sponsor things for you.

Great!  Thank you very much for helping me and it would be amazing if you
could act as sponsor.

> I also have access to s390x hardware to test things out. But my s390x
> specific skills are extremely basic at the moment. I can just about
> ipl things to get me into installer.
> 

That's good to know ;-)  First of all, if you questions regarding s390x,
do not hesitate to ask me or the debian-s390 mailing list.  If you can
IPL the system and get into the installer, you have already master lots
of things.  Within the Linux instance, then, things looks similar to Linux
on other platforms.... maybe except the way how devices are managed.

Let me provide some more insights into device management on the mainframe
because that's one of the fundamental differences to other platforms.

A mainframe is a large system and there can be numerous devices.  These
devices managed through an I/O subsystem, called the channel subsystem.
To handle devices on the channel subsystem, the Linux kernel provides a
dedicated layer, the common I/O layer (CIO).  This layer represents the
maninframe (s390) devices to Linux.  A device on the channel subsystem
is represented by a bus-ID in Linux, for example, 0.0.1224.  The "1234"
portion is the device number ranging from 0000 to FFFF.  Managing this
range of possible devices can be complex.

Due to the complexity, devices are disabled by default. Hence, devices
that the Linux instances require must be enabled first, i.e., the devices
must be set online.  This step can include some device configuration
changes.
After the devices are enabled, they appear to the Linux instance, for
example, as DASDs or FCP devices.  Some device configuration can or must
be performed at enablement.

This particular enablement step is unique to Linux on the mainframe.
After enablement, device management is similar to other Linux platforms.

So that's why there the DASD and the FCP device configuration module: to
enable DASD and FCP devices and block devices and SCSI devices available
to the Linux instance.  Then, they can be partitioned like any other
SCSI disk.


Thanks and kind regards,
  Hendrik

-- 
Hendrik Brueckner
brueckner@linux.vnet.ibm.com      | IBM Deutschland Research & Development GmbH
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