[Bug 1546606] Patch for multipath-tools to load SCSI device handlers before SCSI low-level device drivers (boot time)

[bugproxy]

------- Comment on attachment From mauricfo at br.ibm.com 2016-02-18 13:11 EDT-------


Hi @mathieu-tl,

I'm attaching a patch for multipath-tools as well,
so to avoid any delays and more SCSI errors during boot time.

Tested on another system, attached via FC to DS4800 storage (which uses
RDAC), and with IPR disks (which uses ALUA).

Thanks

** Attachment added: "Patch for multipath-tools to load SCSI device handlers before SCSI low-level device drivers (boot time)"
   https://bugs.launchpad.net/bugs/1546606/+attachment/4574746/+files/multipath-tools_scsi-dh.debdiff

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https://bugs.launchpad.net/bugs/1546606

Title:
  Unable to install Ubuntu 16.04 on Tuleta with multipath setup

Status in hw-detect package in Ubuntu:
  In Progress

Bug description:
  ---Problem Description---
  Unable to succeed in installing  Ubuntu 16.04 on Tuleta with multipath setup; installation hung at scanning disks
   
  == Comment: #11 - Kevin W. Rudd - 2016-02-05 13:13:11 ==

  It looks like the issue in this case involves an RDAC based storage
  controller and I/O errors on the ghost paths.

  == Comment: #23 - Mauricio Faria De Oliveira - 2016-02-17 07:48:23 ==
  Hi Canonical,

  This patch resolves this problem. It's been tested on 16.04.
  Please consider it for uploading. 

  @taco-screen-team, I believe @mathieu-tl would be assigned to this
  one, it it helps.

  
  Testing udeb package:

  	~ # wget http://ausgsa.ibm.com/~mauricfo/public/bugs/bz136625/v1/disk-detect_1.114ubuntu1scsidh1_all.udeb
  	~ # udpkg -i disk-detect_1.114ubuntu1scsidh1_all.udeb 

          Detect disks happened.

  It is working correctly.

  1) The SCSI DH modules are correctly loaded and attached (see
  references count) to SCSI disk.

  
  	~ # lsmod | grep scsi
  	scsi_transport_fc      71759  1 lpfc
  	scsi_dh_alua            9962  16
  	scsi_dh_hp_sw           5252  0
  	scsi_dh_emc             9486  0
  	scsi_dh_rdac            9656  32

  2) The 'Scanning disks' dialog show I/O error dialogs rather than a
  silent, extremely long delay.

          [!] Partition disks

          Error fsyncing/closing /dev/sdag: Input/output error

          Warning!

  	Retry
  	Ignore

          <Go Back>

  == Comment: #26 - Mauricio Faria De Oliveira <mauricfo at br.ibm.com> - 2016-02-17 09:20:28 ==
  Quick summary.

  The long delays are caused due to dmraid scanning the RDAC unowned
  paths to the storage unit (seen in multipath -l as 'ghost' paths).

  They happen in 2 points: during hw-detect/disk-detect and
  partman/init.d/30parted (Scanning disks).

  If you have multipath enabled in the installation, 
  the 2nd delay doesn't happen as the individual SCSI disks (/dev/sdX) are not considered by partman, 
  but the 1st delay does occur *anyway*, as /bin/disk-detect does call dmraid to scan available devices.

  So, the fix is beneficial for both scenarios (multipath enabled and
  disabled; e.g., user forgot to/didn't know he should enable it).

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