[Bug 1538775] Re: multipath-tools-boot relies on scsi_wait_scan module, fails multipath setup

[Mathieu Trudel-Lapierre]

** Also affects: multipath-tools (Ubuntu Trusty)
   Importance: Undecided
       Status: New

** Changed in: multipath-tools (Ubuntu)
       Status: New => Fix Released

** Changed in: multipath-tools (Ubuntu Trusty)
       Status: New => In Progress

** Changed in: multipath-tools (Ubuntu Trusty)
   Importance: Undecided => Medium

** Changed in: multipath-tools (Ubuntu Trusty)
     Assignee: (unassigned) => Mathieu Trudel-Lapierre (mathieu-tl)

** Description changed:

+ [Impact]
+ Users of multipath may see an error message on every boot (when in verbose mode) about the scsi_wait_scan module being unavailable.
+ 
+ [Test case]
+ Boot 14.04 system with multipath-tools-boot. (Multipath devices installed, and the pacakge multipath-tools-boot installed).
+ 
+ [Regression Potential]
+ None. This module has been removed for a long while; as such this has no effect aside from removing an extra error message on boot.
+ 
+ ------
+ 
  Release: Ubuntu 14.04.3 LTS
  Kernel: linux-image-3.16.0-59-generic
  A clean system installed fresh today (2016-01-27)
  
  In attempting to configure a system to boot-from-SAN and enable
  multipath support I ran into an issue whereby despite the multiple paths
  being detected (when running the multipath command from the CLI) the
  configuration wasn't being enabled at boot. After examining /usr/share
  /initramfs-tools/scripts/local-top/multipath I found the following:
  
  verbose && log_begin_msg "Waiting for scsi storage"
  { rmmod scsi_wait_scan ; modprobe scsi_wait_scan ; rmmod scsi_wait_scan ; } >/dev/null 2>&1
  verbose && log_end_msg
  
  The problem appears to be that the scsi_wait_scan module doesn't  exist
  and so there is no wait before the multipath scan is performed. I
  managed to observe this briefly during bootup (with the script edited)
  and could see it performed the scan before sda/sdb was discovered.
  
  I also found a debian bug report indicating the module was removed a
  while back (https://lists.debian.org/debian-
  kernel/2012/05/msg00791.html).
  
  After adding in an artificial delay for testing the multipath command
  does what is expected and configures the paths accordingly. I'm not sure
  what the correct approach is if the scsi_wait_scan module is removed.
  
  I also found that the same local-top script doesnt have the dm-round-
  robin module loaded (but it is included in the initrd by the associated
  hook script), however I'm not sure if that is by design. I know I need
  it for my specific use-case, but don't know if it is deliberately
  excluded to prevent breakage on SAN units that don't support native
  round-robin.

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https://bugs.launchpad.net/bugs/1538775

Title:
  multipath-tools-boot relies on scsi_wait_scan module, fails multipath
  setup

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