[Bug 1468897] Re: multipath creates binding for Removable(USB) drives

[Steve Langasek]

The verification-* tag flip-flop is due to a private conversation about
concerns over the correctness of the test case.  These are resolved, so
marking v-done again.

** Tags removed: verification-failed
** Tags added: verification-done

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https://bugs.launchpad.net/bugs/1468897

Title:
  multipath creates binding for Removable(USB) drives

Status in multipath-tools package in Ubuntu:
  Fix Released
Status in multipath-tools source package in Trusty:
  Fix Committed

Bug description:
  [Impact]
  Users installing with a USB key attached to the installing system, or adding a USB key on an installed system with multipath enabled will see the USB devices picked up by multipath. This is confusing because it changes the paths required to be used to access/mount/format the USB drives to paths under /dev/mapper, with mpath names.

  [Test Case]
  1) Attach a USB key on a system with multipath enabled; either from the installer (booting the installer with USB attached), or on an installed system.
  2) See that the device is picked up by multipath-tools and shows up in the output of 'multipath -ll' and under /dev/mapper with the same name as provided by multipath -ll.

  [Regression Potential]
  Some USB 3.0 devices *can* support multipath; users of such custom configurations will see USB devices not being considered as multipath devices. Other devices which should be considered as multipathed may not be picked up anymore.

  ----

  On a system with a multipath configuration, multipath bindings are
  being created for removable(USB) drives rendering them inaccessible as
  normal removable drives.

  in this case, the usb drive is detected as /dev/sdi:

  # lsblk|grep -A2 sdi
  sdi                        8:128  1  14.7G  0 disk
  ├─sdi1                     8:129  1  14.7G  0 part
  └─mpath4 (dm-9)          252:9    0  14.7G  0 mpath
    └─mpath4-part1 (dm-10) 252:10   0  14.7G  0 part

  # cat /etc/multipath/bindings
  # This file was created by curtin while installing the system.
  mpath0 1IBM     IPR-0   5EC2590000000080
  # End of content generated by curtin.
  # Everything below is maintained by multipath subsystem.
  mpath1 1IBM     IPR-0   5EC2590000000060
  mpath2 1IBM     IPR-0   5EC2590000000040
  mpath3 1IBM     IPR-0   5EC2590000000020
  mpath4 1ADATA   USB Flash Drive

  Upon trying to format /dev/sdi1:

  # mkfs.ext4 /dev/sdi1
  mke2fs 1.42.9 (4-Feb-2014)
  /dev/sdi1 is apparently in use by the system; will not make a filesystem here!

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: multipath-tools 0.4.9-3ubuntu7.2
  ProcVersionSignature: User Name 3.16.0-41.55~14.04.1-generic 3.16.7-ckt11
  Uname: Linux 3.16.0-41-generic ppc64le
  ApportVersion: 2.14.1-0ubuntu3.10
  Architecture: ppc64el
  Date: Thu Jun 25 20:44:13 2015
  ProcEnviron:
   TERM=screen
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: multipath-tools
  UpgradeStatus: No upgrade log present (probably fresh install)

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