patch posted to the kernel-team mailing list:

https://lists.ubuntu.com/archives/kernel-team/2017-June/084718.html

** Description changed:

  [Impact]
  
   * The SES driver causes a long delay in disk discovery when
     a large number of disks is present in the disk enclosure,
     which increases with the number of disks attached.
  
   * This delays the addition and visibility of the disk devices
     to userspace, which among other things causes multipath not
     to have multiple paths, actually, until the disk discovery
     eventually/finally finishes.
  
   * The fix significantly shortens the time taken by the SES
     driver to handle disk discovery, causing no extra delays,
     by removing a superfluous SCSI command sent to enclosure.
  
  [Test Case]
  
   * Load the module to access the enclosure and its disks; e.g.,
  
     $ sudo modprobe mpt3sas
  
   * Notice the interval between the discovery of each disk; e.g., dmesg
  
     $ dmesg -T | grep 'Attached SCSI disk' | tail -n2
     [Thu Jun 1 14:18:30 2017] sd 17:0:100:0: [sdcr] Attached SCSI disk
     [Thu Jun 1 14:18:35 2017] sd 17:0:101:0: [sdcs] Attached SCSI disk
  
   * The interval should be in the same second or so range with the fix.
  
     $ dmesg -T | grep 'Attached SCSI disk' | tail -n2
     [Wed Jun  7 13:11:59 2017] sd 18:0:176:0: [sdly] Attached SCSI disk
     [Wed Jun  7 13:11:59 2017] sd 18:0:175:0: [sdlx] Attached SCSI disk
  
  [Regression Potential]
  
   * The power status of the disks in the enclosure is no longer
     checked during probe time.  However, the patch demonstrates that
     initial value was never used in any way.  So, little regression
     potential.
  
   * Nonetheless, users of SES enclosures which verify the power status
     of disks in the enclosure might _theoretically_ see a problem, iff
     the fix has a problem (which has not been found yet).
  
  [Other Info]
  
   * None at this time.
  
- ==== State: Open by: nguyenp on 31 May 2017 15:46:14 ====
- 
-  Product Name          : OpenPOWER Firmware
-  Product Version       : open-power-SMC-P8DTU-V2.00.GA2-20170126-prod
-  Product Extra         :      op-build-3782262
-  Product Extra         :      hostboot-7fdfb37
-  Product Extra         :      occ-e6e194f
-  Product Extra         :      skiboot-5.4.2
-  Product Extra         :      linux-4.4.24-openpower1-9641b3a
-  Product Extra         :      petitboot-v1.4.0-2f8598b
-  Product Extra         :      p8dtu-xml-9a8fee2
- 
- Cable configuration:
- ====================
- On this P8-Briggs system, I have 2 Seagate Storages running with max 
configuration. There are 84 HDDs drives in each storage. So the total drives is 
168 HDDs for both Seagate storages.
- 
- I connected 2 LSI 9300-8e SAS adapters to 2 Seagate storages with
- alternate cabling for redundancy. See a Figure on the connection below:
- 
- Note:  Each Seagate storage has 2 I/O moudules connection in the back.
-        Both I/O modules from each Seagate does see the same set of HDDs
- 
- Cable connection:
- 
- SAS adapter #1:    port1  ----->  Seagate #1-A I/O module
-                    port0  --------------------------------------> Seagate 
#2-B I/O module
- 
- SAS adapter #2:    port1  ---->  Seagate #2-A I/O module
-                    port0  --------------------------------------> Seagate 
#1-B I/O module
- 
- Ubuntu 16.04.2:
- ===============
- 
- - Running with new kernel Ubuntu 4.8.0-520-generic #550~16.04.1+bz154734
- from Mauricio Faria De Oliveira.
  
  Problem Description:
  ====================
- In this Briggs system, I'm running with new Ubuntu 4.8.0-520-generic 
#550~16.04.1+bz154734 that has fix for Multipath problem. Mauricio helped to 
patch the system with this kernel last week to fix the multipath io_setup 
failed problem in LTCBug154734.
  
  This week, I went ahead and scaled up my test configuration to max
  configuration 2x5U84_Enclosures,_MaxCfg_168HDDs. This time, it hit a
  different issue. The issue is that some multipaths only have a single
  path and no redundancy. Others have multiple paths and redundancy.
- 
- == Comment: #13 - Paul Nguyen - 2017-06-01 15:19:58 ==
- 
- -  I agreed with Mauricio that this problem is a timing problem.
- 
- - I re-ran the test and noticed that it took more than 50 minutes after
- system reboot to discover all disks and to build Multipaths correctly.
- 
- - So for it to take this long, it's going to be a problem.
- 
- - I have gathered all logs and attaching to the bug for Mauricio to look
- and confirm.
- 
- - If there is a workaround or fix for faster probe time then I will try
- it out.
- 
- - Below is more information I captured:
  
  Checkpoint #1:
  ==============
  - system reboot around 2pm (14:00)
  
  Checkpoint # 2:
  ===============
  - It took several minutes for first disk to be detected.
  
- root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | head
- [Thu Jun  1 14:06:48 2017] sd 17:0:1:0: [sdb] Attached SCSI disk
- [Thu Jun  1 14:06:51 2017] sd 17:0:2:0: [sdc] Attached SCSI disk
- [Thu Jun  1 14:06:53 2017] sd 17:0:3:0: [sdd] Attached SCSI disk
- [Thu Jun  1 14:06:57 2017] sd 17:0:4:0: [sde] Attached SCSI disk
- [Thu Jun  1 14:07:00 2017] sd 17:0:5:0: [sdf] Attached SCSI disk
- [Thu Jun  1 14:07:03 2017] sd 17:0:6:0: [sdg] Attached SCSI disk
- [Thu Jun  1 14:07:05 2017] sd 17:0:7:0: [sdh] Attached SCSI disk
- [Thu Jun  1 14:07:08 2017] sd 17:0:8:0: [sdi] Attached SCSI disk
- [Thu Jun  1 14:07:11 2017] sd 17:0:9:0: [sdj] Attached SCSI disk
- [Thu Jun  1 14:07:14 2017] sd 17:0:10:0: [sdk] Attached SCSI disk
- root@smb1p1:~#
- 
- ...
  
  root@smb1p1:~# multipath -ll|grep dm |wc -l
  103
+ 
  root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
  [Thu Jun  1 14:18:30 2017] sd 17:0:100:0: [sdcr] Attached SCSI disk
  [Thu Jun  1 14:18:35 2017] sd 17:0:101:0: [sdcs] Attached SCSI disk
  [Thu Jun  1 14:18:40 2017] sd 17:0:102:0: [sdct] Attached SCSI disk
  [Thu Jun  1 14:18:44 2017] sd 17:0:103:0: [sdcu] Attached SCSI disk
  [Thu Jun  1 14:18:54 2017] sd 17:0:105:0: [sdcv] Attached SCSI disk
  [Thu Jun  1 14:18:59 2017] sd 17:0:106:0: [sdcw] Attached SCSI disk
  [Thu Jun  1 14:19:04 2017] sd 17:0:107:0: [sdcx] Attached SCSI disk
  [Thu Jun  1 14:19:09 2017] sd 17:0:108:0: [sdcy] Attached SCSI disk
  [Thu Jun  1 14:19:14 2017] sd 17:0:109:0: [sdcz] Attached SCSI disk
  [Thu Jun  1 14:19:19 2017] sd 17:0:110:0: [sdda] Attached SCSI disk
- root@smb1p1:~#
- 
- ...
- 
- root@smb1p1:~# multipath -ll|grep dm |wc -l
- 126
- root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
- [Thu Jun  1 14:20:23 2017] sd 17:0:123:0: [sddn] Attached SCSI disk
- [Thu Jun  1 14:20:28 2017] sd 17:0:124:0: [sddo] Attached SCSI disk
- [Thu Jun  1 14:20:33 2017] sd 17:0:125:0: [sddp] Attached SCSI disk
- [Thu Jun  1 14:20:38 2017] sd 17:0:126:0: [sddq] Attached SCSI disk
- [Thu Jun  1 14:20:44 2017] sd 17:0:127:0: [sddr] Attached SCSI disk
- [Thu Jun  1 14:20:48 2017] sd 17:0:128:0: [sdds] Attached SCSI disk
- [Thu Jun  1 14:20:54 2017] sd 17:0:129:0: [sddt] Attached SCSI disk
- [Thu Jun  1 14:20:59 2017] sd 17:0:130:0: [sddu] Attached SCSI disk
- [Thu Jun  1 14:21:04 2017] sd 17:0:131:0: [sddv] Attached SCSI disk
- [Thu Jun  1 14:21:09 2017] sd 17:0:132:0: [sddw] Attached SCSI disk
  root@smb1p1:~#
  
  ...
  
  root@smb1p1:~# multipath -ll|grep dm |wc -l
  142
  root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
  [Thu Jun  1 14:21:54 2017] sd 17:0:141:0: [sdee] Attached SCSI disk
  [Thu Jun  1 14:21:58 2017] sd 17:0:142:0: [sdef] Attached SCSI disk
  [Thu Jun  1 14:22:04 2017] sd 17:0:143:0: [sdeg] Attached SCSI disk
  [Thu Jun  1 14:22:08 2017] sd 17:0:144:0: [sdeh] Attached SCSI disk
  [Thu Jun  1 14:22:14 2017] sd 17:0:145:0: [sdei] Attached SCSI disk
  [Thu Jun  1 14:22:18 2017] sd 17:0:146:0: [sdej] Attached SCSI disk
  [Thu Jun  1 14:22:24 2017] sd 17:0:147:0: [sdek] Attached SCSI disk
  [Thu Jun  1 14:22:29 2017] sd 17:0:148:0: [sdel] Attached SCSI disk
  [Thu Jun  1 14:22:34 2017] sd 17:0:149:0: [sdem] Attached SCSI disk
  [Thu Jun  1 14:22:39 2017] sd 17:0:150:0: [sden] Attached SCSI disk
  root@smb1p1:~#
  
- ...
- 
- root@smb1p1:~# multipath -ll|grep dm |wc -l
- 163
- root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
- [Thu Jun  1 14:23:48 2017] sd 17:0:164:0: [sdfa] Attached SCSI disk
- [Thu Jun  1 14:23:53 2017] sd 17:0:165:0: [sdfb] Attached SCSI disk
- [Thu Jun  1 14:23:58 2017] sd 17:0:166:0: [sdfc] Attached SCSI disk
- [Thu Jun  1 14:24:03 2017] sd 17:0:167:0: [sdfd] Attached SCSI disk
- [Thu Jun  1 14:24:08 2017] sd 17:0:168:0: [sdfe] Attached SCSI disk
- [Thu Jun  1 14:24:13 2017] sd 17:0:169:0: [sdff] Attached SCSI disk
- [Thu Jun  1 14:24:19 2017] sd 17:0:170:0: [sdfg] Attached SCSI disk
- [Thu Jun  1 14:24:23 2017] sd 17:0:171:0: [sdfh] Attached SCSI disk
- [Thu Jun  1 14:24:28 2017] sd 17:0:172:0: [sdfi] Attached SCSI disk
- [Thu Jun  1 14:24:33 2017] sd 17:0:173:0: [sdfj] Attached SCSI disk
  
  ...
- 
- root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
- [Thu Jun  1 14:24:03 2017] sd 17:0:167:0: [sdfd] Attached SCSI disk
- [Thu Jun  1 14:24:08 2017] sd 17:0:168:0: [sdfe] Attached SCSI disk
- [Thu Jun  1 14:24:13 2017] sd 17:0:169:0: [sdff] Attached SCSI disk
- [Thu Jun  1 14:24:19 2017] sd 17:0:170:0: [sdfg] Attached SCSI disk
- [Thu Jun  1 14:24:23 2017] sd 17:0:171:0: [sdfh] Attached SCSI disk
- [Thu Jun  1 14:24:28 2017] sd 17:0:172:0: [sdfi] Attached SCSI disk
- [Thu Jun  1 14:24:33 2017] sd 17:0:173:0: [sdfj] Attached SCSI disk
- [Thu Jun  1 14:24:38 2017] sd 17:0:174:0: [sdfk] Attached SCSI disk
- [Thu Jun  1 14:24:43 2017] sd 17:0:175:0: [sdfl] Attached SCSI disk
- [Thu Jun  1 14:24:48 2017] sd 17:0:176:0: [sdfm] Attached SCSI disk
- root@smb1p1:~#
- 
- root@smb1p1:~# date
- Thu Jun  1 14:27:03 CDT 2017
- root@smb1p1:~# multipath -ll | grep -c 'sd[a-z]\+'
- 168
- root@smb1p1:~#
- 
- Checkpoint #3:
- =============
- 
- - After 34 minutes, multipath -ll command shows paths with single path
- and no redundancy.
- 
- root@smb1p1:~# multipath -ll > multipath.log.06012017.afterReboot
- root@smb1p1:~# cat multipath.log.06012017.afterReboot |more
- 
- 35000c50086a3ca97 dm-161 IBM-ESXS,ST10000NM0226 E
- size=9.0T features='0' hwhandler='0' wp=rw
- `-+- policy='round-robin 0' prio=1 status=active
-   `- 17:0:170:0 sdfg 130:32  active ready running
- 35000c50086bae8bf dm-144 IBM-ESXS,ST10000NM0226 E
- size=9.0T features='0' hwhandler='0' wp=rw
- `-+- policy='round-robin 0' prio=1 status=active
-   `- 17:0:152:0 sdep 129:16  active ready running
- 35000c50086baa42f dm-143 IBM-ESXS,ST10000NM0226 E
- size=9.0T features='0' hwhandler='0' wp=rw
- `-+- policy='round-robin 0' prio=1 status=active
-   `- 17:0:151:0 sdeo 129:0   active ready running
- ...
- 
- Check point #4:
- ===============
  
  - After 43  minutes, multipath -ll command shows some paths with only
  single path and no redundancy and some path with multiple paths and
  redundancy.
  
  root@smb1p1:~# date
  Thu Jun  1 14:43:00 CDT 2017
  root@smb1p1:~# multipath -ll | grep -c 'sd[a-z]\+'
  252
  root@smb1p1:~#
  
- Checkpoint #5:
- ==============
+ ...
  
  - After 47 minutes, multipath -ll command still shows some paths with
  only single path and no redundancy.
  
- root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | head
- [Thu Jun  1 14:06:48 2017] sd 17:0:1:0: [sdb] Attached SCSI disk
- [Thu Jun  1 14:06:51 2017] sd 17:0:2:0: [sdc] Attached SCSI disk
- [Thu Jun  1 14:06:53 2017] sd 17:0:3:0: [sdd] Attached SCSI disk
- [Thu Jun  1 14:06:57 2017] sd 17:0:4:0: [sde] Attached SCSI disk
- [Thu Jun  1 14:07:00 2017] sd 17:0:5:0: [sdf] Attached SCSI disk
- [Thu Jun  1 14:07:03 2017] sd 17:0:6:0: [sdg] Attached SCSI disk
- [Thu Jun  1 14:07:05 2017] sd 17:0:7:0: [sdh] Attached SCSI disk
- [Thu Jun  1 14:07:08 2017] sd 17:0:8:0: [sdi] Attached SCSI disk
- [Thu Jun  1 14:07:11 2017] sd 17:0:9:0: [sdj] Attached SCSI disk
- [Thu Jun  1 14:07:14 2017] sd 17:0:10:0: [sdk] Attached SCSI disk
- root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
- [Thu Jun  1 14:46:15 2017] sd 18:0:112:0: [sdjo] Attached SCSI disk
- [Thu Jun  1 14:46:20 2017] sd 18:0:113:0: [sdjp] Attached SCSI disk
- [Thu Jun  1 14:46:25 2017] sd 18:0:114:0: [sdjq] Attached SCSI disk
- [Thu Jun  1 14:46:31 2017] sd 18:0:115:0: [sdjr] Attached SCSI disk
- [Thu Jun  1 14:46:36 2017] sd 18:0:116:0: [sdjs] Attached SCSI disk
- [Thu Jun  1 14:46:41 2017] sd 18:0:117:0: [sdjt] Attached SCSI disk
- [Thu Jun  1 14:46:46 2017] sd 18:0:118:0: [sdju] Attached SCSI disk
- [Thu Jun  1 14:46:51 2017] sd 18:0:119:0: [sdjv] Attached SCSI disk
- [Thu Jun  1 14:46:56 2017] sd 18:0:120:0: [sdjw] Attached SCSI disk
- [Thu Jun  1 14:47:01 2017] sd 18:0:121:0: [sdjx] Attached SCSI disk
- root@smb1p1:~#
- root@smb1p1:~#
- root@smb1p1:~# date
- Thu Jun  1 14:47:20 CDT 2017
+ 
  root@smb1p1:~# multipath -ll | grep -c 'sd[a-z]\+'
  288
  root@smb1p1:~#
  
- Checkpoint #6:
- ==============
  
  - After 51 minutes after system reboot, looks like all disk are
  discovered and the Multipath is correctly built.
  
  root@smb1p1:~# multipath -ll | grep -c 'sd[a-z]\+'
  336
  
- root@smb1p1:~# date
- Thu Jun  1 14:52:05 CDT 2017
- root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
- [Thu Jun  1 14:50:47 2017] sd 18:0:167:0: [sdlp] Attached SCSI disk
- [Thu Jun  1 14:50:52 2017] sd 18:0:168:0: [sdlq] Attached SCSI disk
- [Thu Jun  1 14:50:57 2017] sd 18:0:169:0: [sdlr] Attached SCSI disk
- [Thu Jun  1 14:51:02 2017] sd 18:0:170:0: [sdls] Attached SCSI disk
- [Thu Jun  1 14:51:07 2017] sd 18:0:171:0: [sdlt] Attached SCSI disk
- [Thu Jun  1 14:51:13 2017] sd 18:0:172:0: [sdlu] Attached SCSI disk
- [Thu Jun  1 14:51:17 2017] sd 18:0:173:0: [sdlv] Attached SCSI disk
- [Thu Jun  1 14:51:22 2017] sd 18:0:174:0: [sdlw] Attached SCSI disk
- [Thu Jun  1 14:51:27 2017] sd 18:0:175:0: [sdlx] Attached SCSI disk
- [Thu Jun  1 14:51:33 2017] sd 18:0:176:0: [sdly] Attached SCSI disk
- root@smb1p1:~#
  
  == Comment: #24 - Mauricio Faria De Oliveira  - 2017-06-06 11:42:59 ==
  Hi Paul,
  
  Per your logs, yes, it's the slowness with the SES driver.
  
  I'll ask Canonical to pick it up for 16.10 and 17.04 so it makes into
  16.04.2 and 16.04.3.
  
  Thanks,
  Mauricio
  
  == Comment: #26 - Mauricio Faria De Oliveira <mauri...@br.ibm.com> - 
2017-06-06 12:06:32 ==
  The patch applies cleanly in the master-next branch of ubuntu-zesty.git and 
ubuntu-yakkety.git.
  Mirroring to Canonical to get a LP bug number, required in the submission 
process.
  
  == Comment: #27 - Mauricio Faria De Oliveira <mauri...@br.ibm.com> - 
2017-06-06 12:07:58 ==
  The commit is [1].
  
  commit 75106523f39751390b5789b36ee1d213b3af1945
  Author: Mauricio Faria de Oliveira <mauri...@linux.vnet.ibm.com>
  Date:   Wed Apr 5 12:18:19 2017 -0300
  
      scsi: ses: don't get power status of SES device slot on probe
  
  [1]
  
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=75106523f39751390b5789b36ee1d213b3af1945

-- 
You received this bug notification because you are a member of Kernel
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https://bugs.launchpad.net/bugs/1696445

Title:
  OpenPower: Some multipaths temporarily have only a single path

Status in linux package in Ubuntu:
  New

Bug description:
  [Impact]

   * The SES driver causes a long delay in disk discovery when
     a large number of disks is present in the disk enclosure,
     which increases with the number of disks attached.

   * This delays the addition and visibility of the disk devices
     to userspace, which among other things causes multipath not
     to have multiple paths, actually, until the disk discovery
     eventually/finally finishes.

   * The fix significantly shortens the time taken by the SES
     driver to handle disk discovery, causing no extra delays,
     by removing a superfluous SCSI command sent to enclosure.

  [Test Case]

   * Load the module to access the enclosure and its disks; e.g.,

     $ sudo modprobe mpt3sas

   * Notice the interval between the discovery of each disk; e.g., dmesg

     $ dmesg -T | grep 'Attached SCSI disk' | tail -n2
     [Thu Jun 1 14:18:30 2017] sd 17:0:100:0: [sdcr] Attached SCSI disk
     [Thu Jun 1 14:18:35 2017] sd 17:0:101:0: [sdcs] Attached SCSI disk

   * The interval should be in the same second or so range with the fix.

     $ dmesg -T | grep 'Attached SCSI disk' | tail -n2
     [Wed Jun  7 13:11:59 2017] sd 18:0:176:0: [sdly] Attached SCSI disk
     [Wed Jun  7 13:11:59 2017] sd 18:0:175:0: [sdlx] Attached SCSI disk

  [Regression Potential]

   * The power status of the disks in the enclosure is no longer
     checked during probe time.  However, the patch demonstrates that
     initial value was never used in any way.  So, little regression
     potential.

   * Nonetheless, users of SES enclosures which verify the power status
     of disks in the enclosure might _theoretically_ see a problem, iff
     the fix has a problem (which has not been found yet).

  [Other Info]

   * None at this time.

  
  Problem Description:
  ====================

  This week, I went ahead and scaled up my test configuration to max
  configuration 2x5U84_Enclosures,_MaxCfg_168HDDs. This time, it hit a
  different issue. The issue is that some multipaths only have a single
  path and no redundancy. Others have multiple paths and redundancy.

  Checkpoint #1:
  ==============
  - system reboot around 2pm (14:00)

  Checkpoint # 2:
  ===============
  - It took several minutes for first disk to be detected.

  
  root@smb1p1:~# multipath -ll|grep dm |wc -l
  103

  root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
  [Thu Jun  1 14:18:30 2017] sd 17:0:100:0: [sdcr] Attached SCSI disk
  [Thu Jun  1 14:18:35 2017] sd 17:0:101:0: [sdcs] Attached SCSI disk
  [Thu Jun  1 14:18:40 2017] sd 17:0:102:0: [sdct] Attached SCSI disk
  [Thu Jun  1 14:18:44 2017] sd 17:0:103:0: [sdcu] Attached SCSI disk
  [Thu Jun  1 14:18:54 2017] sd 17:0:105:0: [sdcv] Attached SCSI disk
  [Thu Jun  1 14:18:59 2017] sd 17:0:106:0: [sdcw] Attached SCSI disk
  [Thu Jun  1 14:19:04 2017] sd 17:0:107:0: [sdcx] Attached SCSI disk
  [Thu Jun  1 14:19:09 2017] sd 17:0:108:0: [sdcy] Attached SCSI disk
  [Thu Jun  1 14:19:14 2017] sd 17:0:109:0: [sdcz] Attached SCSI disk
  [Thu Jun  1 14:19:19 2017] sd 17:0:110:0: [sdda] Attached SCSI disk
  root@smb1p1:~#

  ...

  root@smb1p1:~# multipath -ll|grep dm |wc -l
  142
  root@smb1p1:~# dmesg -T | grep 'sd 1[78]:' |  grep 'Attached SCSI disk' | tail
  [Thu Jun  1 14:21:54 2017] sd 17:0:141:0: [sdee] Attached SCSI disk
  [Thu Jun  1 14:21:58 2017] sd 17:0:142:0: [sdef] Attached SCSI disk
  [Thu Jun  1 14:22:04 2017] sd 17:0:143:0: [sdeg] Attached SCSI disk
  [Thu Jun  1 14:22:08 2017] sd 17:0:144:0: [sdeh] Attached SCSI disk
  [Thu Jun  1 14:22:14 2017] sd 17:0:145:0: [sdei] Attached SCSI disk
  [Thu Jun  1 14:22:18 2017] sd 17:0:146:0: [sdej] Attached SCSI disk
  [Thu Jun  1 14:22:24 2017] sd 17:0:147:0: [sdek] Attached SCSI disk
  [Thu Jun  1 14:22:29 2017] sd 17:0:148:0: [sdel] Attached SCSI disk
  [Thu Jun  1 14:22:34 2017] sd 17:0:149:0: [sdem] Attached SCSI disk
  [Thu Jun  1 14:22:39 2017] sd 17:0:150:0: [sden] Attached SCSI disk
  root@smb1p1:~#

  
  ...

  - After 43  minutes, multipath -ll command shows some paths with only
  single path and no redundancy and some path with multiple paths and
  redundancy.

  root@smb1p1:~# date
  Thu Jun  1 14:43:00 CDT 2017
  root@smb1p1:~# multipath -ll | grep -c 'sd[a-z]\+'
  252
  root@smb1p1:~#

  ...

  - After 47 minutes, multipath -ll command still shows some paths with
  only single path and no redundancy.

  
  root@smb1p1:~# multipath -ll | grep -c 'sd[a-z]\+'
  288
  root@smb1p1:~#


  - After 51 minutes after system reboot, looks like all disk are
  discovered and the Multipath is correctly built.

  root@smb1p1:~# multipath -ll | grep -c 'sd[a-z]\+'
  336

  
  == Comment: #24 - Mauricio Faria De Oliveira  - 2017-06-06 11:42:59 ==
  Hi Paul,

  Per your logs, yes, it's the slowness with the SES driver.

  I'll ask Canonical to pick it up for 16.10 and 17.04 so it makes into
  16.04.2 and 16.04.3.

  Thanks,
  Mauricio

  == Comment: #26 - Mauricio Faria De Oliveira <mauri...@br.ibm.com> - 
2017-06-06 12:06:32 ==
  The patch applies cleanly in the master-next branch of ubuntu-zesty.git and 
ubuntu-yakkety.git.
  Mirroring to Canonical to get a LP bug number, required in the submission 
process.

  == Comment: #27 - Mauricio Faria De Oliveira <mauri...@br.ibm.com> - 
2017-06-06 12:07:58 ==
  The commit is [1].

  commit 75106523f39751390b5789b36ee1d213b3af1945
  Author: Mauricio Faria de Oliveira <mauri...@linux.vnet.ibm.com>
  Date:   Wed Apr 5 12:18:19 2017 -0300

      scsi: ses: don't get power status of SES device slot on probe

  [1]
  
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=75106523f39751390b5789b36ee1d213b3af1945

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