Linux raid software is a good low-cost feature for securing your data. It provides drive mirroring and handling of drives in array.

Last time, I've got a failed drive (failed controller to be exact) that failed a software RAID.

After replacing the drive and rebooting, it was back in the system. But I couldn't put it back in the RAID array. The error message was:

[root@my_server ~]# mdadm --manage /dev/md1 --add /dev/sdd
mdadm: Cannot open /dev/sdd: Device or resource busy