[dm-devel] Clariion CX600 automatic failback support

[goggin, edward]

On Date: Mon, 31 Oct 2005 08:58:06 -0500
Brian Long <brilong at cisco.com> wrote 

> 
> On Wed, 2005-10-26 at 15:37 -0400, Phil Lowden (plowden) wrote:
> > I'm using LVM2 with device-mapper-multipath 0.4.5 on GA 
> RHEL 4 update 2 
> > release, kernel version 2.6.9-22.ELsmp.  Storage is 4 Clariion CX600
> > LUNs, 
> > 2 with a primary path on SP A and 2 on SP B.  HBAs are QLA3240 with
> > firmware 3.03.15 IPX and the RedHat-distributed driver version
> > 8.01.00b5-rh2.
> > 
> > When I disrupt one path by disabling a host or SP switch port,
> > failover works great but failback doesn't happen automatically
> > with the current config (below).  By this I mean
> > when the connection to e.g. SP B is restored, all
> > 4 LUNs stay trespassed to SP A.  Is this by design?
> > Or is there support for automatic failback, i.e.
> > I/O is paused and a trespass is issued to restore
> > the 2 SP B LUNs to their primary paths?
> > 
> > Of course manual failback is possible, but without
> > quiescing I/O I found I was able to munge my LVM2
> > objects up quite nicely.  Manual failback with quiesced 
> > I/O is fine.
> 
> No one has automatic failback working on Clarrion storage?

Unfortunately, this doesn't just work "out of the box" yet.

You need to setup a default failback setting of immediate in the
/etc/multipath.conf configuration file, ...

	defaults {
		failback 	immediate
	}

... or selectively set the failback setting to immediate in the
multipath config file for each EMC CLARiiON logical unit

	multipaths {
		multipath {
			wwid	360061 ...
			failback	immediate
		}
		...
	}

Setting this attribute value for the entire EMC CLARiiON class of
devices via the multipath config file "device" attribute doesn't
work because of a bug (mpp->hwe field is never set for multipathd)
in the multipathd code which is patched to work by the single line
patch below.  Due to the same bug, a patch I submitted many weeks
ago to libmultipath/hwtable.c to setup the default failback policy
for EMC CLARiiON to immediate also does not work.

Once the distributors pick up both this single line change and the
change in hwtable.c, immediate path group failback for CLARiiON
will just work.

-------------------------------------------------------------------
diff --git a/multipathd/main.c b/multipathd/main.c
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -146,6 +146,7 @@ adopt_paths (struct vectors * vecs, stru
 		if (!strncmp(mpp->wwid, pp->wwid, WWID_SIZE)) {
 			condlog(4, "%s ownership set", pp->dev_t);
 			pp->mpp = mpp;
+			mpp->hwe = pp->hwe;
 		}
 	}
 }