NAME
       mdadm - manage MD devices aka Linux Software Raid.

SYNOPSIS
       mdadm [mode] <raiddevice> [options] <component-devices>

DESCRIPTION
       RAID  devices  are  virtual  devices  created  from two or more real block devices. This allows multiple
       devices (typically disk drives or partitions there-of) to be combined into a single device to hold  (for
       example)  a  single  filesystem.   Some RAID levels include redundancy and so can survive some degree of
       device failure.

       Linux Software RAID devices are implemented through the md (Multiple Devices) device driver.

       Currently, Linux supports LINEAR md devices, RAID0 (striping), RAID1 (mirroring), RAID4,  RAID5,  RAID6,
       RAID10, MULTIPATH, and FAULTY.

       MULTIPATH  is  not  a  Software  RAID  mechanism, but does involve multiple devices.  For MULTIPATH each
       device is a path to one common physical storage device.

       FAULTY is also not true RAID, and it only involves one device.  It provides a layer over a  true  device
       that can be used to inject faults.

http://bashconsole.org/man.8.mdadm