Software Raid with MD devices on linux

This article will explain how to convert your one drive system to a raid 1 machine.

Attach the second drive

It is always best to have the second drive same capacity as the first one. We attach a second drive and make sure we see it with fdisk.

Create partitions

Use sfdisk to merely copy the partitions to the new drive.

• sfdisk -d /dev/hda > hda.layout
• sfdisk /dev/hdb < hda.layout

Change partition type

• fdisk /dev/hdb
• l
• t 1 fd
• t 2 fd
• w

Clean up all partitions

• dd if=/dev/zero of=/dev/hdb1 bs=1024 count=100
• dd if=/dev/zero of=/dev/hdb2 bs=1024 count=100

Install Apps

Make sure you have mdadm, rsync, tar and cpio is installed.

Create the Raid volumes

• mdadm --create /dev/md0 --level=1 --raid-devices=2 missing /dev/hdb1
• mdadm --create /dev/md1 --level=1 --raid-devices=2 missing /dev/hdb2

Format the partitions

• mkfs.ext3 /dev/md0
• mkfs.ext3 /dev/md1

Go to run level 1

• init 1

Mount the drive to copy files

• mkdir /mnt/md1
• mount /dev/md1 /mnt/md1
• rsync -avH --delete --exclude 'mnt' --progress -x / /mnt/md1

Replace swap

• swapon -s
• swapoff /dev/hda1
• mkswap /dev/md0
• swapon /dev/md0

Write the raid config

• cat > /mnt/md1/etc/mdadm/mdadm.conf << EOF9
• MAILADDR root
• ARRAY /dev/md0 level=raid 1 num-devices=2 devices=missing,/dev/hdb1
• ARRAY /dev/md1 level=raid 1 num-devices=2 devices=missing,/dev/hdb2

EOF9

Fix fstab in the raid

• vi /mnt/md1/etc/fstab
• /dev/md0 swap swap defaults 0 0
• /dev/md1 / etx3 defaults 1 1