Manually expanding a RAID1 array on Ubuntu

Here are the notes I took while manually expanding an non-LVM encrypted RAID1 array on an Ubuntu machine.

My original setup consisted of a 1 TB drive along with a 2 TB drive, which meant that the RAID1 array was 1 TB in size and the second drive had 1 TB of unused capacity. This is how I replaced the old 1 TB drive with a new 3 TB drive and expanded the RAID1 array to 2 TB (leaving 1 TB unused on the new 3 TB drive).

Partition the new drive

In order to partition the new 3 TB drive, I started by creating a temporary partition on the old 2 TB drive (/dev/sdc) to use up all of the capacity on that drive:

$ parted /dev/sdc
unit s
print
mkpart
print

Then I initialized the partition table and creating the EFI partition partition on the new drive (/dev/sdd):

$ parted /dev/sdd
unit s
mktable gpt
mkpart

Since I want to have the RAID1 array be as large as the smaller of the two drives, I made sure that the second partition (/home) on the new 3 TB drive had:

  • the same start position as the second partition on the old drive
  • the end position of the third partition (the temporary one I just created) on the old drive

I created the partition and flagged it as a RAID one:

mkpart
toggle 2 raid

and then deleted the temporary partition on the old 2 TB drive:

$ parted /dev/sdc
print
rm 3
print

Create a temporary RAID1 array on the new drive

With the new drive properly partitioned, I created a new RAID array for it:

mdadm /dev/md10 --create --level=1 --raid-devices=2 /dev/sdd1 missing

and added it to /etc/mdadm/mdadm.conf:

mdadm --detail --scan >> /etc/mdadm/mdadm.conf

which required manual editing of that file to remove duplicate entries.

Create the encrypted partition

With the new RAID device in place, I created the encrypted LUKS partition:

cryptsetup -h sha256 -c aes-xts-plain64 -s 512 luksFormat /dev/md10
cryptsetup luksOpen /dev/md10 chome2

I took the UUID for the temporary RAID partition:

blkid /dev/md10

and put it in /etc/crypttab as chome2.

Then, I formatted the new LUKS partition and mounted it:

mkfs.ext4 -m 0 /dev/mapper/chome2
mkdir /home2
mount /dev/mapper/chome2 /home2

Copy the data from the old drive

With the home paritions of both drives mounted, I copied the files over to the new drive:

eatmydata nice ionice -c3 rsync -axHAX --progress /home/* /home2/

making use of wrappers that preserve system reponsiveness during I/O-intensive operations.

Switch over to the new drive

After the copy, I switched over to the new drive in a step-by-step way:

  1. Changed the UUID of chome in /etc/crypttab.
  2. Changed the UUID and name of /dev/md1 in /etc/mdadm/mdadm.conf.
  3. Rebooted with both drives.
  4. Checked that the new drive was the one used in the encrypted /home mount using: df -h.

Add the old drive to the new RAID array

With all of this working, it was time to clear the mdadm superblock from the old drive:

mdadm --zero-superblock /dev/sdc1

and then change the second partition of the old drive to make it the same size as the one on the new drive:

$ parted /dev/sdc
rm 2
mkpart
toggle 2 raid
print

before adding it to the new array:

mdadm /dev/md1 -a /dev/sdc1

Rename the new array

To change the name of the new RAID array back to what it was on the old drive, I first had to stop both the old and the new RAID arrays:

umount /home
cryptsetup luksClose chome
mdadm --stop /dev/md10
mdadm --stop /dev/md1

before running this command:

mdadm --assemble /dev/md1 --name=mymachinename:1 --update=name /dev/sdd2

and updating the name in /etc/mdadm/mdadm.conf.

The last step was to regenerate the initramfs:

update-initramfs -u

before rebooting into something that looks exactly like the original RAID1 array but with twice the size.