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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:

[...@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:

[...@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.


[...@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]
[...@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
        }
}

** Affects: multipath-tools (Ubuntu)
     Importance: Undecided
         Status: New

-- 
constantly changes /dev/disk/by-id/{scsi,wwn}-* LUN symlinks with multipathing
https://bugs.launchpad.net/bugs/644489
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