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Re: [dm-devel] DM-Multipath path failure questions..



Kevin,

Correct me if im wrong, but I if I changed the path_grouping_policy to "failover" I lose the ability to aggregate IO traffic across multiple active paths at once. Unfortunately in our situation the performance hit would be undesirable.

With your setup do your backend block device names ever change? Say if you had an extended network outage and had to manually reconnect to the SAN?

-Mike

On Wed, 14 Nov 2007 13:26:32 -0500
"Kevin Foote" <kevin foote gmail com> wrote:

> Mike,
> If you are going for failover things should look like this..
> We go to an Equallogic PS box as well .. through a QLA4052 HBA
> 
> You need to change this line in your /etc/multipath.conf file to
> reflect what you want multipathd to do.
> >         path_grouping_policy    multibus
> should read ...
>          path_grouping_policy    failover
> 
> In turn your maps will look like this ..  (multipath -ll)
> media-oracle (30690a018a0b3d369dd4f04191c4090f9)
> [size=8 GB][features="0"][hwhandler="0"]
> \_ round-robin 0 [active]
>   \_ 2:0:8:0 sdj 8:144 [active][ready]
> \_ round-robin 0 [enabled]
>   \_ 3:0:8:0 sdr 65:16 [active][ready]
> 
> and dmsetup table <dev>
> #> dmsetup table /dev/mapper/media-oracle
> 0 16803840 multipath 0 0 2 1 round-robin 0 1 1 8:144 100 round-robin 0
> 1 1 65:16 100
> 
> will show a multipath failover setup
> 
> 
> -- 
> :wq!
> kevin.foote
> 
> On Nov 14, 2007 1:07 AM, Michael Vallaly <vaio nolatency com> wrote:
> >
> > Hello,
> >
> > I am currently using the dm-multipather (multipath-tools) to allow high-availability / increased capacity to our Equallogic iSCSI SAN. I was wondering if anyone had come across a way to re-instantiate a failed path / paths from a multipath target, when the backend device (iscsi initiator) goes away.
> >
> > All goes well until we have a lengthy network hiccup or non-recoverable iSCSI error in which case the multipather seems to get wedged. The path seems to get stuck in a [active][faulty] state and the backend block device (sdX) actually gets removed from the system. I have tried reconnecting the iSCSI session, after this happens, and get a new (different IE: sdg vs. sdf) backend block level device, but the multipather never picks it up / never resumes IO operations, and I generally have then to power cycle the box.
> >
> > We have anywhere from 2 to 4 iSCSI sessions open per multipath target, but even one path failing seems to cause the whole multipath to die. I am hoping there is a way to continue on after a path failure, rather than the power cycle. I have tried multipath-tools 0.4.6/0.4.7/0.4.8, and almost every permutation of the configuration I can think of. Maybe I am missing something quite obvious.
> >
> > Working Multipather
> > <snip>
> > mpath89 (36090a0281051367df57194d2a37392d5) dm-4 EQLOGIC ,100E-00
> > [size=300G][features=1 queue_if_no_path][hwhandler=0]
> > \_ round-robin 0 [prio=2][active]
> >  \_ 5:0:0:0  sdf 8:80  [active][ready]
> >  \_ 6:0:0:0  sdg 8:96  [active][ready]
> > </snip>
> >
> > Wedged Multipather (when a iSCSI session terminates) (All IO queues indefinitely)
> > <snip>
> > mpath94 (36090a0180087e6045673743d3c01401c) dm-10 ,
> > [size=600G][features=1 queue_if_no_path][hwhandler=0]
> > \_ round-robin 0 [prio=0][enabled]
> >  \_ #:#:#:#  -   #:#   [active][faulty]
> > </snip>
> >
> > Our multipath.conf looks like this:
> > <snip>
> > defaults {
> >         udev_dir                /dev
> >         polling_interval        10
> >         selector                "round-robin 0"
> >         path_grouping_policy    multibus
> >         getuid_callout          "/lib/udev/scsi_id -g -u -s /block/%n"
> >         #prio_callout            /bin/true
> >         #path_checker            readsector0
> >         path_checker            directio
> >         rr_min_io               100
> >         rr_weight               priorities
> >         failback                immediate
> >         no_path_retry           fail
> >         #user_friendly_names     no
> >         user_friendly_names     yes
> > }
> >
> > blacklist {
> >         devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st|sda)[0-9]*"
> >         devnode "^hd[a-z][[0-9]*]"
> >         devnode "^cciss!c[0-9]d[0-9]*[p[0-9]*]"
> > }
> >
> >
> > devices {
> >         device {
> >                 vendor                  "EQLOGIC"
> >                 product                 "100E-00"
> >                 path_grouping_policy    multibus
> >                 getuid_callout          "/lib/udev/scsi_id -g -u -s /block/%n"
> >                 #path_checker            directio
> >                 path_checker            readsector0
> >                 path_selector           "round-robin 0"
> >                 ##hardware_handler        "0"
> >                 failback                immediate
> >                 rr_weight               priorities
> >                 no_path_retry           queue
> >                 #no_path_retry           fail
> >                 rr_min_io               100
> >                 product_blacklist       LUN_Z
> >         }
> > }
> >
> > </snip>
> >
> > Thanks for your help.
> >
> > - Mike Vallaly
> >
> >
> >
> >
> >
> > --
> > dm-devel mailing list
> > dm-devel redhat com
> > https://www.redhat.com/mailman/listinfo/dm-devel
> >
> 
> --
> dm-devel mailing list
> dm-devel redhat com
> https://www.redhat.com/mailman/listinfo/dm-devel


-- 

Michael Vallaly
Senior System Administrator
CashNetUSA
200 W Jackson Blvd, Suite 2400
Chicago, IL 60606
mvallaly cashnetusa com
(W) 312-568-4230 
(P) 312-933-9589
(C) 847-769-5568

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