[dm-devel] Re: User specific priorities on for iscsi paths doesn't seem to work
Akshay Lal
alal at cleversafe.com
Fri Aug 7 21:31:17 UTC 2009
Akshay Lal wrote:
> Mike Snitzer wrote:
>> On Fri, Aug 07 2009 at 5:07pm -0400,
>> Akshay Lal <alal at cleversafe.com> wrote:
>>
>>
>>> Mike Snitzer wrote:
>>>
>>>> On Fri, Aug 07 2009 at 4:25pm -0400,
>>>> Akshay Lal <alal at cleversafe.com> 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
>>
>
> I tried out John's approach as well and it still seems to be giving me
> the similar results to what I mentioned before, i.e., replicating
> multibus
>
>
> Priority list:
> --------------
> 192.168.7.103:3260-iscsi-iqn.2008-07.com.cleversafe:vault-2 5
> 192.168.7.106:3260-iscsi-iqn.2008-07.com.cleversafe:vault-2 10
> 192.168.7.103:3260-iscsi-iqn.2008-07.com.cleversafe:vault-1 10
> 192.168.7.106:3260-iscsi-iqn.2008-07.com.cleversafe:vault-1 5
>
> iSCSI disk associated with iSCSI sessions:
> ------------------------------------------
> Target: iqn.2008-07.com.cleversafe:vault-1
> Current Portal: 192.168.7.106:3260,1
> Persistent Portal: 192.168.7.106:3260,1
> Attached scsi disk sdb State: running
> Current Portal: 192.168.7.103:3260,1
> Persistent Portal: 192.168.7.103:3260,1
> Attached scsi disk sdd State: running
>
> Target: iqn.2008-07.com.cleversafe:vault-2
> Current Portal: 192.168.7.106:3260,1
> Persistent Portal: 192.168.7.106:3260,1
> Attached scsi disk sdc State: running
> Current Portal: 192.168.7.103:3260,1
> Persistent Portal: 192.168.7.103:3260,1
> Attached scsi disk sde State: running
>
>
> 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][enabled]
> \_ 84:0:0:0 sdb 8:16 [active][ready]
> \_ 86:0:0:0 sdd 8:48 [active][ready]
>
>
>
> Versions being used:
> dm-multipath: device-mapper-multipath-0.4.7-23.el5_3.4
> kernel: 2.6.29.6
>
>
Sorry I forgot to add the multipath conf file
/etc/multipath.conf :
---------------------
# Blacklist all devices by default. Remove this to enable multipathing
# on the default devices.
#blacklist {
# devnode "*"
#}
##
## Defaults for the multipath daemon
##
#
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 /sbin/mpath_prio_alt %n"
path_checker tur
# rr_min_io 128
max_fds 8192
rr_weight uniform
failback immediate
no_path_retry queue
user_friendly_names yes
}
devices {
device {
vendor "dummy"
product "dummy"
prio_callout "/sbin/mpath_prio_alt %n"
}
}
--
Akshay Lal
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