What you see (the multipath message) is from a kernel module that gets
loaded. That does not necessarily mean it is really used. That is the
way that dmraid, lvm, multipath and mdadm work. Only mdadm is different
in using different kernel driver modules than the rest.

But in general the commands are responsible for reading meta-data from
the devices and detecting whether those contain logical devices they can
handle. Then the info is used to create a simpler representation of that
which is passed to kernel drivers. And those create the logical disks
that you then can use.

The debug data you get unfortunately does not really give a hint why the
raid is not detected. Mind, at that stage the kernel is not yet
involved. The fact that the device-mapper kernel driver has different
versions is not surprising for different kernels. The more important
number would be the ioctl-version and that is the same. But still I do
not think dmraid is already talking to device-mapper at that stage.

So the only visible difference in the debug is that one is longer than
the other (btw, the man page mentions you might get more details when
repeating the -d option, like -d -d -d). The only way to guess which
disks it looks at might be to compare the offsets to disk size. But that
is not very reliable.

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https://bugs.launchpad.net/bugs/1611277

Title:
  Kernel Shipped With Ubuntu 16.04.1 Cannot Recognize fakeRaid

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