[Bug 1540407] Comment bridged from LTC Bugzilla

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------- Comment From thorsten.diehl at de.ibm.com 2016-02-29 08:50 EDT-------
Regarding the above strange behaviour in #5:
On a 4.4.0-8 system freshly installed (not updated from 4.4.0-7) with libzfcphbaapi0 installed the paths are recoverd and re-added as expected, as already described in case #2. And again, with case #1 the problem is reproducable.

What is this libzfcphbaapi0 package doing undercover? Normally it has no
interatice with multipath daemon. Does it change anything in the
multipath configuration?

Adding the libzfcphbaapi0 package to prevent symptoms of this bug can
not be the solution and it might be just by chance, that the symptom
vanished. I talked to zfcp development, and they confirmed that.

As already promised, I will continue some long term tests (cable pull
and other path loosing scenarios) on a 4.4.0-8 system with multipath-
tools_0.5.0+git1.656f8865-4 and kpartx_0.5.0+git1.656f8865-4. Results
should be available by tomorrow.

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https://bugs.launchpad.net/bugs/1540407

Title:
  multipathd drops paths of a temporarily lost device

Status in multipath-tools package in Ubuntu:
  New

Bug description:
  == Comment: #0 - Thorsten Diehl <thorsten.diehl at de.ibm.com> - 2016-02-01 08:57:28 ==
  # uname -a
  Linux s83lp31 4.4.0-1-generic #15-Ubuntu SMP Thu Jan 21 22:19:04 UTC 2016 s390x s390x s390x GNU/Linux

  # dpkg -s multipath-tools|grep ^Version:
  Version: 0.5.0-7ubuntu9

  # cat /etc/multipath.conf
  defaults {
      default_features "1 queue_if_no_path"
      user_friendly_names yes
      path_grouping_policy multibus
      dev_loss_tmo 2147483647
      fast_io_fail_tmo 5
  }

  blacklist {
      devnode '*'
  }

  blacklist_exceptions {
      devnode "^sd[a-z]+"
  }

  ---------------------------------------
  On a z Systems LPAR with a single LUN, 2 zfcp devices, 2 storage ports, and the following multipath topology:

  mpatha (36005076304ffc3e80000000000003050) dm-0 IBM,2107900
  size=1.0G features='1 queue_if_no_path' hwhandler='0' wp=rw
  `-+- policy='round-robin 0' prio=1 status=active
    |- 0:0:0:1079001136 sda 8:0  active ready running
    |- 0:0:1:1079001136 sdb 8:16 active ready running
    |- 1:0:0:1079001136 sdc 8:32 active ready running
    `- 1:0:1:1079001136 sdd 8:48 active ready running

  I observed the following:
  When I deconfigure one of the two zfcp devices (e.g. via chchp -c 0, or directly on the HMC), the multipathd removes the two paths via these devices from the pathgroup after 10 seconds. When the zfcp devices comes back, it runs through zfcp error recovery and is being set up properly, and also the mid layer objects are looking fine. However, the multipathd does not add them to the path group again.

  Expected behaviour: multipathd does not remove the paths from topology
  list, but holds them as "failed faulty offline" until dev_loss_tmo
  timout is reached (which is infinite here).

  I discussed this already with zfcp development, and it looks most
  likely as a problem with multipathd, rather than zfcp or mid-layer.

  Easy to reproduce: you need two zfcp devices, one LUN, and preferably
  two ports on the storage server (WWPNs). Configure LUN via 2 zfcp
  devices * 2 WWPNs = 4 paths.

  This can be also reproduced on a z/VM guest. Instead of configuing the
  CHPID off, just detach one zfcp device and re-attach it after 30....60
  seconds. Same problem.

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