I recently switched my home server from Windows Server 2003 to Ubuntu 10.10. The machine is an older Shuttle box I’ve had tucked away in various places over the past few years.
The plan was to disable the BIOS “fakeRAID”, install Ubuntu on one of the drives, copy my data over to it and then have the other disk join the new Linux software RAID array. I figured out the procedure on a VirtualBox before attempting it on my actual machine.
Install the server with NODMRAID and partition the drive with no LVM, that is partition with “Guided – use entire disk”. We can’t have devicemapper getting in the way.
Install on first hard disk (/dev/sda). If there’s any data you need off the other disk, now’s the time to mount it and copy it over.
To start, we need the mdadm package.
sudo apt-get install mdadm
You need two modules to be loaded at boot-time, raid1 and md. In the kernel included with Ubuntu 10.10, md was compiled in, so I didn’t need to worry about loading it as a module.
I verified this by checking the kernel’s config:
fgrep CONFIG_MD /boot/config-$(uname -r)
Add the module raid1 to the /etc/raid1
sudo nano /etc/modules
Let’s load the raid1 module
sudo modprobe raid1
To ensure it is loaded:
lsmod | grep raid1
So, it seems we’re ready for prepare our other disk. A neat little trick is to use sfdisk to dump the partition table of one disk to configure another.
sudo sfdisk -d /dev/sda > sda.out sudo sfdisk /dev/sdb < sda.out
but sfdisk responds with “I don’t like these partitions – nothing changed.” Well, excuse me, sfdisk, but I don’t like your attitude. (Yes, I’m arguing with a disk utility now) So, I added the –force flag. It grudgingly copied the partition table for me. I verified it by comparing the output of sfdisk -l /dev/sda and sfdisk -l /dev/sdb.
Change the partition type of the Linux partition(s) to “Linux raid autodetect”
sudo sfdisk --change-id /dev/sdb 1 fd
We’re ready to create the array. We specify a RAID 1 array with 2 devices. The first is missing and the second is /dev/sdb1:
sudo mdadm --create /dev/md0 --level=1 --raid-devices=2 missing /dev/sdb1
Now, we need an mdadm.conf. It seems like the way to do this is with
sudo cp /etc/mdadm/mdadm.conf /etc/mdadm/mdadm.oldconf sudo cp /etc/mdadm/mdadm.conf mdadm.conf mdadm --detail --scan >> mdadm.conf
It will put in a parameter metadata=00.90 that will cause warnings later. Apparently, this is a bug and it is safe to remove it. After editing it, I copied back to where it belongs.
sudo cp mdadm.conf /etc/mdadm/mdadm.conf
Now, we format the raid volume
mkfs -t ext4 /dev/md0
Find out the UUID of the array
sudo blkid
Make a copy of /etc/fstab in your home directory and change root to mount to the UUID of the array. Don’t change the real /etc/fstab quite yet.
Add a custom setup in GRUB2, I’m going to edit a copy of this file in my home directory too.
cp /etc/grub.d/40_custom 09_swraid1_setup nano 09_swraid1_setup
Details here, but here’s what I added to my file:
menuentry 'Ubuntu, with Linux 2.6.35-22-server' --class ubuntu --class gnu-linux --class gnu --class os {
recordfail
insmod raid
insmod mdraid
insmod ext2
set root='(md0)'
linux /boot/vmlinuz-2.6.35-22-server root=/dev/md0 ro quiet
initrd /boot/initrd.img-2.6.35-22-server
}
This differs from the linked article in that ‘2.6.35-22-server’ is my kernel release version (the one that ships with Ubuntu server) and I’m booting from md0.
Back to the physical console.
sudo telinit 1
Copy the above temp files (fstab and 09_swraid1_setup) to their actual locations
update-grub
Adjust ramdisk
update-initramfs -u
Ensure GRUB2 is on /dev/sdb and sda
grub-install /dev/sdb
grub-install /dev/sda
Mount the array on /tmparray
mount /dev/md0 /tmparray
rsync -aqxP / /tmparray
Restart and we have now booted off the array!
Change the partition type of sda now
sudo sfdisk --change-id /dev/sda 1 fd
Add it to the array:
mdadm --add /dev/md0 /dev/sda1
Welcome to the party, /dev/sda! Let’s watch it sync:
watch cat /proc/mdstat
Our special GRUB entry is no longer needed
rm -f /etc/grub.d/09_swraid1_setup update-grub update-initramfs -u
Done.
I worked out the kinks in the virtual machine and documented it in a draft of this post. I used it as my guide when performing the install on the actual machine. It worked perfectly.
Update, Feb 25, 2011: Clarification in response to comments.
