Cannot add disk to software raid “–re-add fails”

Just found a new bug on the latest mdadm-3.2.2-9.el6.x86_64 release in centos6.2!

Once you remove a partition from a software raid (fail/remove) you can’t add it back. Error message is:

“mdadm: /dev/sdxx reports being an active member for /dev/mdx, but a –re-add fails”

All you need to do is zero the md info on the partition with: mdadm –zero-superblock /dev/sda1

and then you can add it back to the raid device with: mdadm /dev/md0 –add /dev/sda1