Comment 10 for bug 1567602

------- Comment From <email address hidden> 2016-04-15 13:18 EDT-------
Meanwhile, with kernel 4.4.0-18 and installler version 447, the situation is different:
While the problem originally occured in installer, is happens now, when the target system is being IPLed.

The "switch" (to avoid the word "reason") is the kernel module scsi_dh_alua.
When scsi_dh_alua is loaded, the auto LUN scanning upon activating a zfcp device with NPIV LUNs causes that not all LUNs are detected. I assume, that not the kernel module itself is the problem, but t seems to trigger the problem.

A very easy way to reproduce this is as follows:
have a system installed with kernel 4.4.0-18 (almost GA). Have two NPIV enabled zfcp adaptors (on different PCHIDs) that can access the same (few) LUNs each. Then:

root@s8330005:~# lscss |grep 1732/03
0.0.1905 0.0.0012 1732/03 1731/03 80 80 ff 60000000 00000000
0.0.1945 0.0.0013 1732/03 1731/03 80 80 ff 61000000 00000000
root@s8330005:~# lsmod |grep scsi_dh
root@s8330005:~# chccwdev -e 1905
Setting device 0.0.1905 online
Done
root@s8330005:~# lszfcp -D
0.0.1905/0x50050763070845e3/0x4082405300000000 0:0:0:1079197826
0.0.1905/0x50050763070845e3/0x4083405300000000 0:0:0:1079197827
0.0.1905/0x50050763070845e3/0x4084405300000000 0:0:0:1079197828
0.0.1905/0x50050763070845e3/0x4085405300000000 0:0:0:1079197829
root@s8330005:~# lsmod |grep scsi_dh
root@s8330005:~# modprobe scsi_dh_alua
root@s8330005:~# chccwdev -e 1945
Setting device 0.0.1945 online
Done
root@s8330005:~# lszfcp -D
0.0.1905/0x50050763070845e3/0x4082405300000000 0:0:0:1079197826
0.0.1905/0x50050763070845e3/0x4083405300000000 0:0:0:1079197827
0.0.1905/0x50050763070845e3/0x4084405300000000 0:0:0:1079197828
0.0.1905/0x50050763070845e3/0x4085405300000000 0:0:0:1079197829
0.0.1945/0x50050763071845e3/0x4082405300000000 1:0:0:1079197826
/sbin/lszfcp: line 244: /sys/bus/ccw/drivers/zfcp/0.0.1945/host1/rport-1:0-0/target1:0:0/1:0:0:1079197827//hba_id: No such file or directory
/sbin/lszfcp: line 245: /sys/bus/ccw/drivers/zfcp/0.0.1945/host1/rport-1:0-0/target1:0:0/1:0:0:1079197827//wwpn: No such file or directory
/sbin/lszfcp: line 246: /sys/bus/ccw/drivers/zfcp/0.0.1945/host1/rport-1:0-0/target1:0:0/1:0:0:1079197827//fcp_lun: No such file or directory
0.0.1945/0x50050763071845e3/0x4082405300000000 1:0:0:1079197827
root@s8330005:~#

When a zfcp attached SCSI LUN is used for installation, (almost?) all scsi_dh modules are loaded upon activation of the zfcp device. This causes some LUNs not to be detected.
If I get acces to that system an blacklist the scsi_dh_alua module, the IPL works as expected ( i.e. all the LUNS are detected properly).