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
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