Building my new NAS I am using a single laptop disk (for now, possibly an SSD later) for my OS and will by adding several 1 TB disks into a RAID. While in Webmin trying to setup the “Linux RAID” feature I ran into an error:
The kernel RAID status file /proc/mdstat does not exist on your system
This means that mdadm was not installed on the box, so via the console I ran
apt-get install mdadm
I didn’t want the base OS to be mirrored so I set the first screen to “none” (instead of “all”) and moved through the prompts (dare I say wizard?). After this I refreshed the module list and “Linux RAID” was installed and ready to use!