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

["Kevin Foote" <kevin foote gmail com>]

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
>
>
>
>
>
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