In a mdadm RAID-5 setup I have to replace a disk whose health is deteriorating (although not yet kicked out my mdadm).
So I added a new disk with
mdadm /dev/md0 --add /dev/sdf
shows the new disk correctly as a spare.
mdamd /dev/md0 --replace /dev/sda
mdadm starts rebuilding, but after a while stops. That is, the process is still there, the disk led on the system lights continuously without flickering, but nothing seems to happen anymore, and
mdadm --detail /dev/md0
hangs forever. Also the system won’t shutdown properly (I have to do a hard reset).
Nothing can be seen in the journal or in the dmesg output.
To be sure I did a new try with the RAID-system unmounted, but the result is the same.
The data on the disk can be read: I made a full backup before issuing the replacement.
Any idea what might be happening here?