[Linux-cluster] GNBD Configuration Question

[Curt Moore]

On 2/13/06, Benjamin Marzinski <bmarzins at redhat.com> wrote:
> On Fri, Feb 10, 2006 at 01:03:36PM -0600, Curt Moore wrote:
> > Hello all.
> >
> > I've been experimenting with RH Cluster Suite and GFS and have come
> > upon a few questions which I hope the list will be able to help.
> > Kudos to all of the developers, RHCS and GFS are really cool!
> >
> > To my question, I'm trying to setup a storage network with GFS and
> > GNBD using a 3 layered approach as shown in Figure 5 in the following
> > link:
> >
> > http://www.redhat.com/magazine/008jun05/features/gfs/#fig=multipath
> >
> > and also here:
> >
> > http://www.redhat.com/docs/manuals/csgfs/browse/rh-gfs-en/s1-ov-perform.html#S2-OV-MODPRICE
> >
> > Obviously, the intent is to eliminate any SPOF for the storage network.
> >
> > For the sake of example, let's say that I have 2 GNBD servers
> > connected directly to the SAN, snode001 and snode002.
> >
> > If I export the the same SAN block device from these 2 GNBD servers
> > for load sharing purposes and snode001 fails, how do the GNBD clients
> > importing that block device from snode001 know that they can also find
> > that block device on snode002?  Is this somehow handled at a lower
> > level by configuring a resource within the RH Cluster Suite?
> >
> > I've scoured the list archives and found the following example, using
> > multipath, which seems to come very close:
> >
> > http://www.redhat.com/archives/linux-cluster/2005-April/msg00065.html
> >
> > However, the documentation states that multipath GNBD cannot be used
> > with GFS 6.1:
> > http://www.redhat.com/docs/manuals/csgfs/browse/rh-gfs-en/ch-gnbd.html
> >
> > Is there another way of accomplishing this without using multipath or
> > am I misunderstanding the concept of how multipath is utilized in this
> > setup?
>
> The only way for a gnbd client to access the same data served up by two gnbd
> servers is to use some multipath implementation. Currently there is no
> mulipath implementation that supports gnbd devicse. sorry.
>
> -Ben
>

Ben,

Thanks for your reply.

That's a bummer.  So, older versions of GFS supported multipath but
6.1 somehow broke this?

I suppose I could accomplish this using iSCSI SAN devices or perhaps
even setup a few servers running as iSCSI targets which are in turn
physically connected to the FC SAN.  Either of these scenarios should
support multipath, correct?

Has anyone had good or bad experiences when trying to run multipath on
iSCSI devices for a fault tolerant SAN?

Thanks,
-Curt

>
> > Any feedback would be appreciated.
> >
> > Thanks!
> > -Curt
> >
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