Comment 38 for bug 1611277

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.