[CLUG-tech] IBM SAN multipath

Michael Wood michael at frogfoot.com
Wed Dec 12 11:09:30 SAST 2007

On Wed, Dec 12, 2007 at 10:27:21AM +0200, Adrian Moisey wrote:
> Hi
> > A few more questions. The answers may or may not help me help you, but
> > bear with me.
> Unfortunately they took my server away and I won't have one to play with soon.
> > > I've got an IBM SAN plugged into 2 single port HBA QLogic cards, but
> > > I'm failing at getting multipath going.  I haven't much experience in
> >
> > What type of server are the HBAs in? Also an IBM? OR perhaps a Dell?
> > Or homebuilt or other brand? Also what model? And what model/type etc.
> > is the SAN?
> A 2900 Dell box.  The SAN is a DS3400 IBM.

My experience with a DS4300 (note, NOT the DS3400 that Adrian has but
perhaps it works the same way) is that you can get to each LUN via
either path, but one is the preferred path.  When you create the LUNs
you can specify which controller should handle each one.

So I am pretty sure that the normal Linux multipath stuff should work.
(We were not using the DS4300 with Linux.)

On Linux, you can do multipath using multipathd (which as far as I
understand it is the way it's supposed to be done these days) or in the
HBA driver itself.  e.g. Qlogic drivers are able to do multipath so that
you only see one SCSI device per array instead of seeing sda and sdb and
then using multipathd to join them together.

Adrian, your initial message about this said that multipath was
complaining that one of the paths was down.  I assume you checked all
the cables etc? :)

Also, I'm not sure that round-robin is the correct option to use if you
have a primary/secondary path situation instead of two equal paths.  I
used multipathd on an HP EVA storage array, and the paths are all equal,
so I haven't tried any other scheduler.

> > Also, I'm not sure about the IBM ones, but quite a few SANs come with
> > their own proprietary multipathing software/drivers. You might want to
> > check that's not a requirement for yours to work.
> Will look into it
> Can't get the other info for you until they get me a new server
> > Fianlly, what distro and output of uname -a
> Stock Ubuntu Gutsy.
> Sorry for the lack of info :/

Michael Wood <michael at frogfoot.com>

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