Growing RAID 1

November 18th, 2009, 9:45 pm

The hard drive in my father’s computer finally died. It was a 74GB Raptor which was originally mine. He wanted to get his computer running as fast as possible, so I hopped on Newegg and ordered a 320GB drive for him.

For kicks, I decided to see if the drive was still under warranty. To my surprise it was! The drive was about 4 years old. I went through the RMA process and just got a replacement a few days ago.

I figured I would use the drive for my / (root),  /home, and swap partitions.

However, on my 2x 750GB HDs I had three raid arrays. One for /boot, / (root), and /home. I wanted to make the /home raid array into /data, but I no longer needed /boot or / (root).

Therefore I need to remove the two unneeded raid arrays and expand the last one, /home.

My RAID 1 Setup looked like this: (2x750GB HD)

  • md0 = /boot (250MB)
  • md1=/ (root) (20GB)
  • md2=/home (640GB)

Goal:

  • md0 = /data (680GB)

In order to do this, we need to stop the other raids that we no longer need.

In this case, md0 and md1:

mdadm --stop /dev/md0
mdadm --stop /dev/md1

Look at /dev/md2:

Personalities : [raid1]
md2 : active raid1 sda3[1] sdb3[0]
      732571904 blocks [2/2] [UU]

There are two partitions that make up md2:  sda3 and sdb3

We need to fail and remove one of the drives in the array. Lets pick sdb3

mdadm -f /dev/md2 /dev/sdb3
mdadm -r /dev/md2 /dev/sdb3

The first command fails the drive and the second command removes the drive.

Once this is done repartition /dev/sdb with one partition (type FD; Linux RAID Autodetect) that uses the whole disk.

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1       91201   732572001   fd  Linux raid autodetect

Now we need to add the bigger partition back into the array.

mdadm --add /dev/md2 /dev/sdb1

This step will take a long time (2-10hrs; maybe longer) because the array has to resync

You can monitor the progress by running this command: watch cat /proc/mdstat

After the resync finishes, repeat the same steps, but for sda

mdadm -f /dev/md2 /dev/sda3
mdadm -r /dev/md2 /dev/sda3
fdisk /dev/sda
mdadm --ad /dev/md2 /dev/sda1

Now we can grow the array by running:

mdadm --grow /dev/md2 --size=max

Lastly we have to expand the file system, but first we want to run a filesystem check to make sure there are no errors.

fsck /dev/md2

And now to resize the filesystem (for ext2, ext3, ext4)

resize2fs /dev/md2

All that is left to do now is modify system files such as /etc/mdadm.conf to get rid of the two unneeded arrays (md0 and md1). Also, I would recommended renaming /dev/md2 to /dev/md0


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