Package: mdadm

"mdadm" package binaries on CentOS:

/sbin/mdadm /sbin/mdmon /usr/sbin/raid-check

You may install this package on CentOS with yum install mdadm

"mdadm" package binaries on Debian:

/sbin/mdadm /sbin/mdmon

You may install this package on Debian with apt-get install mdadm