[dm-devel] rdac priority checker changing priorities

[Hannes Reinecke]

Hi Lucas,

Lucas Brasilino wrote:
> Hi
> 
> I don't know if I'm misundertanding something. I've got an DS4700 and I'm
> switching from RDAC[1] to multipath, since it's natively supported in
> the distribution I use
> here (SLES 10 SP2).
> 
> Since RDAC[1] works perfect, I'm trying to use 'rdac' priority in multipath.
> 
> My /etc/multiconf.conf is quite tiny, since I'm building it step-by-step :-) :
> 
> blacklist {
> 	devnode "^sda[0-9]*"
> }
> 
> defaults {
> 	user_friendly_names	yes
> 	prio			rdac
> 	path_checker		tur
> }
> 
> multipaths {
> 	multipath {
> 		wwid	3600a0b8000327b900000107549f85224
> 		alias	mpath0
> 	}
> }
> 
> I think that using 'prio rdac' makes multipath to use 'mpath_prio_rdac' tool.
> 
>  # multipath -v2 -ll
> mpath0 (3600a0b8000327b900000107549f85224) dm-0 IBM,1814      FAStT
> [size=140G][features=1 queue_if_no_path][hwhandler=1 rdac]
> \_ round-robin 0 [prio=6][active]
>  \_ 9:0:0:0  sdb 8:16  [active][ready]
> \_ round-robin 0 [prio=1][enabled]
>  \_ 10:0:0:0 sdc 8:32  [active][ghost]
> 
> So the first path has priority 6, as I can confirm:
> 
> # mpath_prio_rdac /dev/sdb
> 6
> # mpath_prio_rdac /dev/sdc
> 1
> 
> After the first path (prio=6) failure I get:
> 
> # multipath -v2 -ll
> sdb: rdac prio: inquiry command indicates error
> mpath0 (3600a0b8000327b900000107549f85224) dm-0 IBM,1814      FAStT
> [size=140G][features=1 queue_if_no_path][hwhandler=1 rdac]
> \_ round-robin 0 [prio=0][enabled]
>  \_ 9:0:0:0  sdb 8:16  [failed][faulty]
> \_ round-robin 0 [prio=1][enabled]
>  \_ 10:0:0:0 sdc 8:32  [active][ghost]
> 
> Ok.. working great, activating the second path. But after the faulty
> path is restored:
> 
> # multipath -v2 -ll
> mpath0 (3600a0b8000327b900000107549f85224) dm-0 IBM,1814      FAStT
> [size=140G][features=1 queue_if_no_path][hwhandler=1 rdac]
> \_ round-robin 0 [prio=2][enabled]
>  \_ 9:0:0:0  sdb 8:16  [active][ghost]
> \_ round-robin 0 [prio=5][active]
>  \_ 10:0:0:0 sdc 8:32  [active][ready]
> 
> Second path is now priority!!! And of course does not fails back! By
> the way, my LUN is configured in
> DS4700 in sort a way that the first path *is* the path to preferred controller.
> 
> I think path priorities should not change. If so first path goes back
> to 'active' status.
> Am I misunderstanding something ? Or messing things up?
> 
You are using an old version of multipathing for SLES10 SP2.
This had a bug triggering priority inversion on RDAC.
Please update to the latest version.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare at suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)