On Fri, 2009-08-07 at 17:21 -0400, Mike Snitzer wrote:
> On Fri, Aug 07 2009 at 5:07pm -0400,
> Akshay Lal <alal@xxxxxxxxxxxxxx> wrote:
>
> > Mike Snitzer wrote:
> >> On Fri, Aug 07 2009 at 4:25pm -0400,
> >> Akshay Lal <alal@xxxxxxxxxxxxxx> wrote:
> >>
> >>
> >>> I'm having a few issues with path priorities. It seems that the
> >>> choice of path to use during I/O is independent of the user defined
> >>> priorities for each path.
> >>>
> >>> I am setting the priorities by executing writing a script that is
> >>> used by prio_callout. This seems to work when I execute multipath
> >>> -ll since all the specified priorities show up correctly. (the
> >>> path_grouping_policy being used is failover)
> >>>
> >>
> >> ...
> >>
> >>
> >>> Is there something I'm doing wrong? I would like to be able to define
> >>> the priorities per device, and ensure that data only traverses on
> >>> the lower priority path when
> >>> a) a failure to the first path (path with a higher priority) occures
> >>> b) no other path with a higher priority exists
> >>>
> >>
> >> Do things behave as you'd like if you change path_grouping_policy to
> >> 'group_by_prio'?
> >>
> >> Mike
> >>
>
>
> > Mike:
> >
> > It seems that if I were to set the path_grouping_policy to
> > "group_by_prio", then it seems to be working similar to a multibus
> > configuration. What I would like is for within a single multipath group,
> > (say mpath1), specify a primary path and an alternate/failover path. If
> > I can make this configurable via user land tool that'd be great. In this
> > vein, I had considered priorities with hope that if I can set the
> > priority of a certain path within a group then the path with the highest
> > priority will always be chosen and the other path (with the lower
> > priority) will only come into play when the primary goes down.
> >
> > Below is the output of the multipath -ll & conf file when setting the
> > path_grouping_policy to group_by_prio.
> >
> >
> > multipath -ll:
> > --------------
> > mpath2 (244534e3833623961) dm-1 DSNET,Dispersed Store
> > [size=47G][features=1 queue_if_no_path][hwhandler=0][rw]
> > \_ round-robin 0 [prio=15][enabled]
> > \_ 85:0:0:0 sdc 8:32 [active][ready]
> > \_ 87:0:0:0 sde 8:64 [active][ready]
> > mpath1 (244534e3266616134) dm-0 DSNET,Dispersed Store
> > [size=47G][features=1 queue_if_no_path][hwhandler=0][rw]
> > \_ round-robin 0 [prio=15][active]
> > \_ 84:0:0:0 sdb 8:16 [active][ready]
> > \_ 86:0:0:0 sdd 8:48 [active][ready]
> >
> >
> > /etc/multipath.conf:
> > --------------------
> > defaults {
> > udev_dir /dev
> > polling_interval 1
> > selector "round-robin 0"
> > path_grouping_policy group_by_prio
> > getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
> > prio_callout "/bin/bash
> > /root/MultipathScripts/mpath_prio_alt %n"
> > path_checker tur
> > rr_min_io 128
> > max_fds 8192
> > rr_weight priorities
> > failback immediate
> > no_path_retry queue
> > user_friendly_names yes
> > }
>
>
> Please don't top-post.
>
> I'm pretty sure John meant to say "group_by_prio" rather than "failover"
> in his initial reply to this thread. John originally got this insight
> (dummy device section et. al. applies to RHEL 5.3) back in April:
>
> https://www.redhat.com/archives/dm-devel/2009-April/msg00157.html
>
> Which multipath/distro are you using?
>
> Mike
<snip>
Actually, we are using failover in our environment. Perhaps I have
missed something but it is working well for us as far as I can tell. We
have a single path unless it fails in which case we go to the next path
in priority order. We are handling load balancing across paths in a
different way as we found the performance of multibus was less than we
could achieve otherwise. Then again, this is not an area of expertise
for me. Thanks - John
--
John A. Sullivan III
Open Source Development Corporation
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