[dm-devel] path state change

[Murthy, Narasimha Doraswamy (STSD)]

Hi,

In the process of testing path failover I noticed the following:

a) when the path is made unavailable(/dev/sdd) for a logical device
"mp1" on a  multipath target, the status of the path becomes
[faulty][active]

                mp1

[size=1 GB][features="0"][hwhandler="0"]

\_ round-robin 0 [enabled]

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

\_ round-robin 0 [active][first]

  \_ 1:0:0:1 sdd  8:48    [faulty ][active]

 

b) When an dd is executed on /dev/mapper/mp1, the state of the paths is
as follows

                mp1

[size=1 GB][features="0"][hwhandler="0"]

\_ round-robin 0 [active][first]

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

\_ round-robin 0 [enabled]

  \_ 1:0:0:1 sdd  8:48    [faulty ][failed]

 

 

b) Now if the path is made available for the same logical device
(/dev/sdd), the status is as follows

                mp1

[size=1 GB][features="0"][hwhandler="0"]

\_ round-robin 0 [active][first]

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

\_ round-robin 0 [enabled]

  \_ 1:0:0:1 sdd  8:48    [ready ][failed]

 

Note the path /dev/sdd has become [ready][failed] not [ready][active].

 

Now if path /dev/sda is made unavailable, then if "dd" is run on
/dev/mapper/mp1, it returns with input/output error, as none of the path
will be in [ready][active] state. The following is the state now:

 

                mp1

[size=1 GB][features="0"][hwhandler="0"]

\_ round-robin 0 [active][first]

  \_ 0:0:0:1 sda  8:0     [faulty]][active]

\_ round-robin 0 [enabled]

  \_ 1:0:0:1 sdd  8:48    [ready ][failed]

 

Kindly explain me what the two states for each path infer. Like
[ready][active] or [faulty][active] or [faulty][failed] or
[ready][failed]. Also let me know how to failover to other path
(/dev/sdd) as it shows [ready][failed] status. If I execute just
"multipath" tool  from the command prompt the states get updated
properly as

 

                mp1

[size=1 GB][features="0"][hwhandler="0"]

\_ round-robin 0 [active][first]

  \_ 0:0:0:1 sda  8:0     [faulty]][active]

\_ round-robin 0 [enabled]

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

 

After this I will be able to do IO using "dd".  I suspect that I haven't
configured my hotplug to call "multipath" tool as the path is made
available/unavailable.  I am not sure on where I get hotplug script for
multipath and how to configure hotplug for calling the "multipath" tool.
I appreciate if anyone can help me out in this regard.

 

Thanks and regards

Murthy

 

 

 

 

 

 

 

 

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