Mdadm is the modern tool most Linux distributions use these days to manage software RAID arrays.
Some common usages of mdadm to manage software raid arrays
Verifying the status of the RAID arrays
Checking the status/health of an RAID (also useful for checking a RAID is rebluilding):
cat /proc/mdstat
or
mdadm --detail /dev/md0
Create a new RAID array
Create (mdadm –create) is used to create a new array:
mdadm --create --verbose /dev/md0 --level=1 /dev/sda1 /dev/sdb2
If you get “mdadm: no raid-devices specified” try adding the raid-devices option
mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb2
Remove a disk from an array
We can’t remove a disk directly from the array, unless it is failed, so we first have to fail it (unless it already is):
Fail sda1
mdadm --fail /dev/md0 /dev/sda1
Remove sda1 from array
mdadm --remove /dev/md0 /dev/sda1
Add a disk to an existing array
Normally done when replacing a failed disk:
mdadm --add /dev/md0 /dev/sdb1
Stop and delete a RAID array
If we want to completely remove a raid array we have to stop if first and then remove it:
mdadm --stop /dev/md0
mdadm --remove /dev/md0
Remove Superblock
mdadm --zero-superblock /dev/sda