The mdadm tool manages MD devices, such as Linux Software RAID.
In most cases the package is pulled in during the kernel installation as a dependency when a RAID is present.
# emerge mdadm
Configuring mdadm is done via the
/etc/mdadm.conf file. By default, after installation this file is entirely commented out. One may remove the comment hash
# in front of the line that most suits the RAID in use and alter the line to point to the correct devices, or add a new line, based on the examples given.
To start mdadm at boot, add it to the default runtime level:
# rc-update add mdadm boot
Not doing so results in unbootable system.
If you're upgrading an existing system to Funtoo, backup the existing
/etc/mdadm.conf file to a secure location and copy it back prior to rebooting into the new install.
mdadm can be very tricky to administer for novices. Install Webmin and use its webinterface to create and use a new RAID.