lk/data/mdadm.md

RAID5

You will need 4 disks and the mdadm package. The total size will be equal to the disks x 3, because one will be used for redundancy.

sudo mdadm --create --verbose /dev/md127 --level=5 --raid-devices=4 /dev/sdb /dev/sdc /dev/sdd /dev/sde

Note the variable parts:

• The name of the device could be /dev/md12 or whatever
• The number of devices could be larger, but must be at least 4 for raid 5
• We end by listing all devices in the new md device.

Now look at how the raid status:

cat /proc/mdstat

This will increase until the entire thing is fine.

Check the health of your mdadm array:

sudo mdadm --detail /dev/md127

You should see State : clean. If you see it is degraded, then a disk has broken.

Replacing a Disk

First, prepare the disk with both a gpt partition table, and a partition:

sudo parted --script /dev/sdb mklabel gpt mkpart primary 1MiB -2048s

Add the appropriate file system to it, e.g.:

sudo mkfs.ext4 /dev/sdb1

Then finally, add the disk:

sudo mdadm --add /dev/md127 /dev/sdb1