Joseph Herlant
version 1.0.0, 2014-07-05 : Initial version

You’ll need the mdadm package here.

Creating a logical /dev/md0 RAID 5 device from /dev/sdb1, /dev/sdc1 and /dev/sdd1 partitions.

# First verify that all the partitions have been created using fdisk
fdisk -l
# If not, create them
fdisk /dev/sdd
# Finally create the RAID
mdadm -Cv /dev/md0 --level=5 -n3 /dev/sdb1 /dev/sdc1 /dev/sdd1

Then verify the status using

# First verify the md number taken by the RAID
cat /proc/mdstat
# Then get the details
mdadm --detail /dev/md0

Fail a given disk of md0 using

mdadm /dev/md0 -f /dev/sdb1

Remove a disk from the array using

mdadm /dev/md0 -r /dev/sdb1

Or combine them using: mdadm -v /dev/md0 -f /dev/sdb1 -r /dev/sdb1

Add a disk in the array using

mdadm /dev/md0 -a /dev/sdb1

Add then the RAID device to LVM using the classic pvcreate /dev/md0

Drop the array using

# First switch array offline after removing from LVM using pvremove
mdadm -vS /dev/md0
# Then remove the device (seems not needed on Centos 6.5)
mdadm --remove /dev/md0
# Finally, zero the superblock
mdadm --zero-superblock /dev/sdb1 /dev/sdc1 /dev/sdd1

Find stopped RAID arrays:

# mdadm -v --examine --scan
ARRAY /dev/md/0  level=raid5 metadata=1.2 num-devices=3 UUID=187b93af:44c4a179:06ae2b77:59e32205 name=RHEL01:0

Changing the device name from a given device. Here our device is called /dev/md127 and we would like to start it as /dev/md0, do:

# First switch array offline after removing from LVM using pvremove
mdadm -vS /dev/md127
# Then scan the offline devices to get the UUID
mdadm -v --examine --scan
# And use this UUID to start the device with the new device name
mdadm --assemble --run -u 187b93af:44c4a179:06ae2b77:59e32205 /dev/md0
# And check the drive is now available from /proc/mdstat
cat /proc/mdstat
# If you want your new configuration to be preserved between reboots
mdadm --detail --brief /dev/md0 >> /etc/mdadm.conf
# And remove the line related to the old configuration of this device if exists
# in this configuration file.
/boot can only use basic partitions or logical RAID 1 because GRUB don’t undestand the other types of RAID.