ZFS lost mirror device

ZFS lost mirror device.txt

I'm using zfs for mirroring on my hypervisors, mitingated from lvm/mdadm-raid1.

Some days ago my zfs-mirroring stopped working, leading to a degraded state. ZFS said,
one of the mirror-devices, which should be normally named sda4, is now called
238018108320 or something like this, and on the last row of zpool status, theres an 
entry like "was: /dev/sda4".

Zfs can't open the device again, I tried:

zpool offline data /dev/sda4
and
zpool dattach data /dev/sda4
than again
zpool attach data /dev/sda4
which leads to:

"zfs cannot open /dev/sda4: The device or resource is busy"

BUSY???

So I searched for the issue, and looked at /proc/mdstat...

There is /dev/sda4 listed as md2, and /dev/sda4 as spare-device
for this raid (without any active devices).

So I stopped /dev/md2 and attached /dev/sda4 again to my zfs.

Strange enouth, that mdadm can lock a device from beeing used
by zfs, the partition type of this partition was BF, means
solaris, not raid-autodetect. I think, mdadm should not do anything
with partitions which don't got the right partition type!