[dm-devel] regarding path failback using HSV110 array.

[Murthy, Narasimha Doraswamy (STSD)]

Hi Alasdair,

As per yesterday's teleconf, I am sending the snapshot of the
/var/log/messages, which has the messages logged when testing the basic
failback functionality.  The testing is conducted on the host with RHEL
U1 and single controller of HP Storageworks HSV110 array. As each HSV110
controller has 2 ports, we effectively see 2 paths per lun. I am using
0.4.5.44 version of multipath tools.  

 

Following is the observation during testing the path failback.

 

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 [active][best]

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

\_ round-robin 0 [enabled]

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

 

b) When an dd is executed on /dev/mapper/mp1 (dd if=/dev/zero
of=/dev/devmapper/mp1), the state of the paths is as follows

mp1

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

\_ round-robin 0 [enabled]

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

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

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

 

 

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

mp1

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

\_ round-robin 0 [enabled]

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

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

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

 

Note the path "/dev/sda" has become [ready][failed] not [ready][active].
For this to change to [ready][active], "multipath -v0" needs to be
executed manually.

 

d) Now if path "/dev/sdd" 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 [enabled][best]

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

\_ round-robin 0 [enabled]

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

 

 

If "multipath -v0" executed from the command prompt the states get
updated properly as

 

mp1

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

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

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

\_ round-robin 0 [enabled]

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

 

After this I will be able to do IO using "dd".   How do we make the path
state update properly with out manually invoking "multipath -v0"? 

I am not sure on how to get the debug build of multipath and multipathd
binaries, if the information in the messages.txt is insufficient, I need
to test with the debug build and send the new log.

 

Any help in resolving this problem is appreciated.

 

Thanks and regards

Murthy

 

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