[Bug 644489] Re: constantly changes /dev/disk/by-id/{scsi, wwn}-* LUN symlinks with multipathing

[Peter Petrakis]

We had another incident of this fault, but with an EMC Clariion CX4-120.
After eliminating LVM, and moving to a default MP config. It wasn't
until we removed the "change" rule to the 95-multipath.tools script
that the udev error messages ceased. I'm convinced that this
approach for the boot scripts is broken now and requires additional
scrutiny.

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Title:
  constantly changes /dev/disk/by-id/{scsi,wwn}-* LUN symlinks with
  multipathing

Status in “multipath-tools” package in Ubuntu:
  Confirmed
Status in “udev” package in Ubuntu:
  New

Bug description:
  Binary package hint: udev

  udevd constantly changes LUN device node symlinks (devices/LUNs, not
  the partition nodes) in /dev/disk/by-id. udevd uses ~15% of CPU and
  system time is using ~50-60%.

  For example:

  [jwm at syslog01.roch.ny:pts/0 /dev/disk/by-id> ls -l wwn-0x60a98000486e5339576f596675735354 wwn-0x60a98000486e5339576f596675744c36 scsi-360a98000486e5339576f596675735354 scsi-360a98000486e5339576f596675744c36; sleep 1; echo '======'; ls -l wwn-0x60a98000486e5339576f596675735354 wwn-0x60a98000486e5339576f596675744c36 scsi-360a98000486e5339576f596675735354 scsi-360a98000486e5339576f596675744c36
  lrwxrwxrwx 1 root root 9 2010-09-21 16:12 scsi-360a98000486e5339576f596675735354 -> ../../sde
  lrwxrwxrwx 1 root root 9 2010-09-21 16:12 scsi-360a98000486e5339576f596675744c36 -> ../../sdf
  lrwxrwxrwx 1 root root 9 2010-09-21 16:12 wwn-0x60a98000486e5339576f596675735354 -> ../../sde
  lrwxrwxrwx 1 root root 9 2010-09-21 16:12 wwn-0x60a98000486e5339576f596675744c36 -> ../../sdf
  ======
  lrwxrwxrwx 1 root root 9 2010-09-21 16:12 scsi-360a98000486e5339576f596675735354 -> ../../sdg
  lrwxrwxrwx 1 root root 9 2010-09-21 16:12 scsi-360a98000486e5339576f596675744c36 -> ../../sdh
  lrwxrwxrwx 1 root root 9 2010-09-21 16:12 wwn-0x60a98000486e5339576f596675735354 -> ../../sdg
  lrwxrwxrwx 1 root root 9 2010-09-21 16:12 wwn-0x60a98000486e5339576f596675744c36 -> ../../sdh

  All other device nodes stay the same, such as the device nodes for the
  partitions:

  [jwm at syslog01.roch.ny:pts/0 /dev/disk/by-id> ls -l scsi-360a98000486e5339576f596675735354-part1; sleep 1; echo '======'; ls -l scsi-360a98000486e5339576f596675735354-part1
  lrwxrwxrwx 1 root root 10 2010-09-21 15:47 scsi-360a98000486e5339576f596675735354-part1 -> ../../sdg1
  ======
  lrwxrwxrwx 1 root root 10 2010-09-21 15:47 scsi-360a98000486e5339576f596675735354-part1 -> ../../sdg1

  
  I'm not entirely sure whether this is udev's problem or something related to multipathing. Our most recent experience with multipathing is the last LTS release (hardy), which doesn't exhibit this behavior given similar configurations.

  
  [jwm at syslog01.roch.ny:pts/0 ~> sudo multipath -ll
  rootvol (360a98000486e5339576f596675735354) dm-1 NETAPP  ,LUN           
  [size=36G][features=1 queue_if_no_path][hwhandler=0]
  \_ round-robin 0 [prio=8][active]
   \_ 2:0:2:0 sda 8:0   [active][ready]
   \_ 3:0:2:0 sde 8:64  [active][ready]
  \_ round-robin 0 [prio=2][enabled]
   \_ 3:0:3:0 sdg 8:96  [active][ready]
   \_ 2:0:3:0 sdc 8:32  [active][ready]
  syslog-data (360a98000486e5339576f596675744c36) dm-0 NETAPP  ,LUN           
  [size=1.0T][features=1 queue_if_no_path][hwhandler=0]
  \_ round-robin 0 [prio=8][active]
   \_ 2:0:2:1 sdb 8:16  [active][ready]
   \_ 3:0:2:1 sdf 8:80  [active][ready]
  \_ round-robin 0 [prio=2][enabled]
   \_ 3:0:3:1 sdh 8:112 [active][ready]
   \_ 2:0:3:1 sdd 8:48  [active][ready]
  [jwm at syslog01.roch.ny:pts/0 ~> cat /etc/multipath.conf 
  multipaths {
          multipath {
                  wwid            360a98000486e5339576f596675735354
                  alias           rootvol
          }
          multipath {
                  wwid            360a98000486e5339576f596675744c36
                  alias           syslog-data
          }
  }

  devices {
          device {
                  vendor                  "NETAPP  "
                  product                 "LUN "
                  path_checker            tur
                  path_grouping_policy    group_by_prio
                  prio_callout            "/sbin/mpath_prio_netapp /dev/%n"
                  failback                immediate
                  rr_min_io               128
                  no_path_retry           queue
          }
  }

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