Useful MDADM commands

Notes: /dev/hdb{1,2,3} are current RAID members. /dev/hdb4 is a new "drive"

#RAID Status
cat /proc/mdstat
mdadm --detail /dev/md0

#Copy Partition Structure for a New Drive (Useful when adding a new drive)
sfdisk -d /dev/hdb1 | sfdisk /dev/hdb3

#Add another drive to an array
mdadm /dev/md0 --add /dev/hdb4
mdadm /dev/md0 --grow -n 4
resize2fs /dev/md0
xfs_growfs /mnt/RAID (for XFS)

#Replace a failed drive
mdadm /dev/md0 --fail /dev/hdb2
mdadm /dev/md0 --remove /dev/hdb2
//Partition the new drive same as others (info above)
mdadm /dev/md0 --add /dev/hdb4

#Increase size of array (all the drives have gotten bigger)
mdadm /dev/md0 --grow --size=max
resize2fs /dev/md
xfs_growfs /mnt/RAID (for XFS)

#Remove RAID array
//fail and remove all the drives (see replace a failed drive above)
//unmount array
mdadm --stop /dev/md0