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RAID 1

Create a RAID 1 system of 2 disks and 2 partitions

In the following examples we are going to use sdb and sdc for the disc to use in the RAID. Adapt it to your situation.

Create the partitions

fdisk /dev/sdb
  • p check the partition table
  • n create partition (ex +128M)
  • t filesystem
  • a bootflag
  • w write 

Set the RAID1 system on the 2 partitions

mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sdb2 /dev/sdc2

Check the RAID-DEVICES

cat /proc/mdstat

Make the file system

mkfs.ext3 /dev/md0
mkfs.ext4 /dev/md1

Mount the disks

mkdir /mnt/md0
mkdir /mnt/md1
mount /dev/md0 /mnt/md0/
mount /dev/md1 /mnt/md1/

Copy the data of Home

cd /home
tar c * | tar x -C /mnt/md1

Find the UUID of the 1st partition

blkid
/dev/md1: UUID="3968404e-6571-4671-a157-9113a9f2fcba" TYPE="ext4"

Make md1 be the home directory

emacs /etc/fstab
# /home was on /dev/sda9 during installation
UUID=3968404e-6571-4671-a157-9113a9f2fcba /home ext3 defaults 0 2

 

Add new Hard drive

Connect the new hard disk and boot a system.

This will create on the new drive a partition table identical to the one of the existing working drive (this will also copy GRUB).

(Assuming that /dev/sda is the existing working drive and /dev/sdb is the newly added drive)

dd if=/dev/sda of=mbr.bin bs=512 count=1
dd if=mbr.bin of=/dev/sdb bs=512 count=1

Check the status of the RAID devices to see the device numbers

cat /proc/mdstat

Add the appropriate partition of the new drive to the RAID devices, repeat for each RAID device.

mdadm --manage --add /dev/md0 /dev/sdb1

Remove an md device

Removing /dev/md1 as an example ...

Find which block devices the md device is built on

mdadm --detail /dev/md1

Stop the device:

mdadm --stop /dev/md1

For each block device the device is built on (here /dev/sda2):

mdadm --zero-superblock /dev/sda2

Finally remove the device:

mdadm --remove /dev/md1

Common to all RAID

Start the arrays at once

Some linux system integrated an mdadm tool called mdadm-startall. You can install it if not already done.

It doesn't require any argument and will assemble all the md drives found.

mdadm-startall
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