topic difference b/w the values in multipath output in Operating System - Linux

difference b/w the values in multipath output

Maaz — Sat, 16 May 2009 12:37:45 GMT

there are differences b/w the output of 'multipath -ll' and 'multipath -l' .. why ?

Why the difference in the value of 'prio' ? .
And in case of '-ll' it is "[ready]" while in '-l' its "[undef]" .. why ?

# multipath -ll

3600508b40006e2cc0000c00000400000dm-0 HP,HSV200

[size=305G][features=0][hwhandler=0]

\_ round-robin 0 [prio=100][active]

\_ 0:0:3:1 sdb 8:16 [active][ready]

\_ 1:0:3:1 sdd 8:48 [active][ready]

\_ round-robin 0 [prio=20][enabled]

\_ 0:0:2:1 sda 8:0 [active][ready]

\_ 1:0:2:1 sdc 8:32 [active][ready]

NFL-PRD:~ # multipath -l

3600508b40006e2cc0000c00000400000dm-0 HP,HSV200

[size=305G][features=0][hwhandler=0]

\_ round-robin 0 [prio=0][active]

\_ 0:0:3:1 sdb 8:16 [active][undef]

\_ 1:0:3:1 sdd 8:48 [active][undef]

\_ round-robin 0 [prio=0][enabled]

\_ 0:0:2:1 sda 8:0 [active][undef]

\_ 1:0:2:1 sdc 8:32 [active][undef]

Re: difference b/w the values in multipath output

Matti_Kurkela — Sun, 17 May 2009 12:38:06 GMT

"multipath -l" gets its information from sysfs and device mapper only. It does not invoke path checkers.

"multipath -ll" gets information from all relevant sources, including path checkers. If your storage system is of active/passive type (i.e. the servers should prefer the currently "active" paths, instead of just using any available path), and your multipath configuration is not yet aware of it, this may cause disk I/O delays.

In other words: depending on the type of your storage system, "multipath -ll" may or may not be slightly unsafe if your multipath policy is configured incorrectly; "multipath -l" does not give as much information but should always be safe to use.

MK

Re: difference b/w the values in multipath output

Maaz — Sun, 17 May 2009 17:20:56 GMT

thanks MK for help, reply and suggestion.

please also let me know the difference b/w the output and values

there are differences b/w the output of 'multipath -ll' and 'multipath -l' .. why ?
Why the difference in the value of 'prio' ? .
And in case of '-ll' it is "[ready]" while in '-l' its "[undef]" .. why ?

and one more thing I got the 4 columns(instead of three)
1, round-robin
2, 0
3, [prio=value] ### extra column
4, [enabled/active]

I mean as per the http://kbase.redhat.com/faq/docs/DOC-2644;jsessionid=640A0C46553CAB54A761E7C3A620B475.ab46478d

For each path group:
_ scheduling_policy [path_group_priority_if_known][path_group_status_if_known]

so in my case
scheduling_policy is "round-robin"
path_group_priority is "0"
path-group_status "[active/enabled]"

but [prio=0/100] is what ?

Regards