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...

In this example I have two hard drives, /dev/sda and /dev/sdb, with the partitions /dev/sda1 and /dev/sda2 as well as /dev/sdb1 and /dev/sdb2. /dev/sda1 and /dev/sdb1 make up the RAID1 array /dev/md0. /dev/sda2 and /dev/sdb2 make up the RAID1 array /dev/md1. /dev/sda1 + /dev/sdb1 = /dev/md0 /dev/sda2 + /dev/sdb2 = /dev/md1 /dev/sdb has failed, and we want to replace it.   2 How Do I Tell If A Hard Disk Has Failed? If a disk has failed, you...