Resolving LVM: Unrecognised LVM device type 259

Trying to create a md raid1 device for 2 phyiscal 1TB disks failed unexpectedly with a strange (and very undescriptive error, that is only revealed when running with the verbose option (-vvv): Wiping internal VG cache /dev/md0p2: Skipping: Unrecognised LVM device type 259 Device /dev/md0p2 not found (or ignored by filtering).

The problem seems to be that the type 259 is simply not recognized, although it is defined in /proc/devices and known as blkext there. So adding this to /etc/lvm/lvm.conf in the devices section: types = [ "blkext", 64 ]

After adding this the mdadm command to create the md device succeeds: mdadm --create /dev/md0 --level=1 --raid-disks=2 /dev/sda /dev/sdb