mdadm
manages Linux software RAID arrays
TLDR
Create RAID array
$ sudo mdadm --create /dev/md/MyRAID --level raid1 --raid-devices 2 /dev/sda1 /dev/sdb1
Stop array$ sudo mdadm --stop /dev/md0
Mark disk failed$ sudo mdadm --fail /dev/md0 /dev/sda1
Remove disk$ sudo mdadm --remove /dev/md0 /dev/sda1
Add disk$ sudo mdadm --assemble /dev/md0 /dev/sdc1
Show details$ sudo mdadm --detail /dev/md0
Clear RAID metadata$ sudo mdadm --zero-superblock /dev/sda1
SYNOPSIS
mdadm [mode] [OPTIONS] device
DESCRIPTION
mdadm manages Linux software RAID arrays (md devices). It can create, assemble, monitor, grow, and manage arrays of various RAID levels including RAID 0, 1, 5, 6, and 10.
PARAMETERS
--create device
Create a new array--assemble device
Assemble a previously created array--stop device
Stop an active array--detail device
Display detailed information about an array--examine device
Examine RAID superblock on a component device--fail device component
Mark a component as failed--remove device component
Remove a component from an array--add device component
Add a component to an array--level level
RAID level (0, 1, 5, 6, 10, linear)--raid-devices n
Number of active devices in array--zero-superblock device
Erase RAID superblock from a device
CAVEATS
Creating an array destroys existing data on component devices. RAID is not a backup solution. RAID 5/6 require minimum 3/4 devices respectively. Always monitor arrays for failed drives.
HISTORY
mdadm is the modern Linux software RAID management tool, replacing older raidtools.