This is tested on Debian Squeeze, but should work on most Debian derived distributions and on other Linux distributions with small changes. I have written almost the same guide some years ago, but I wanted to add an extra disk to my QNAP NAS and decided to write it down again. Requirements; 2 identical disks
Installation
Partition and install Debian GNU/Linux onto first disk (sda in my case) if you don’t have a running system already. Configure the system and make sure everything works. Install the software raid administration tool ‘mdadm’
# apt-get install mdadm Partition second unused disk (sdb) with same layout as first disk (sda) sfdisk --dump /dev/sda | sfdisk --force /dev/sdb Reboot into single-user mode to make sure partition table is re-read and to avoid having running services when copying data.
Plan your RAID devices
We will create a RAID device for each partition. I have the following layout on my first disk:
Device Boot Start End Blocks Id System /dev/sda1 * 1 43 340992 83 Linux /dev/sda2 43 182402 1464795137 5 Extended /dev/sda5 43 773 5858304 83 Linux /dev/sda6 773 1137 2928640 83 Linux /dev/sda7 1137 1514 3022848 82 Linux swap / Solaris /dev/sda8 1514 1562 389120 83 Linux /dev/sda9 1562 182402 1452592128 83 Linux
This means that I will end up with 6 different RAID devices:
/dev/md0 (sda1 + sdb1) mounted on / /dev/md1 (sda5 + sdb5) mounted on /usr /dev/md2 (sda6 + sdb6) mounted on /var /dev/md3 (sda7 + sdb7) used for swap /dev/md4 (sda8 + sdb8) mounted on /tmp /dev/md5 (sda9 + sdb9) mounted on /home
Create RAID devices
Before we create any RAID devices, we should change the parition type from Linux/SWAP to fd Linux raid auto. Do this with the fdisk command. My /dev/sdb partition table looks like this now:
Device Boot Start End Blocks Id System /dev/sdb1 * 1 43 340992 fd Linux raid autodetect /dev/sdb2 43 182402 1464795137 5 Extended /dev/sdb5 43 773 5858304 fd Linux raid autodetect /dev/sdb6 773 1137 2928640 fd Linux raid autodetect /dev/sdb7 1137 1514 3022848 fd Linux raid autodetect /dev/sdb8 1514 1562 389120 fd Linux raid autodetect /dev/sdb9 1562 182402 1452592128 fd Linux raid autodetect
It would not work if we created the RAID devices with both involved disk drives, but we have the possibility to create a failed RAID device with only the partition from the new unused disk. We use the word ‘missing’ in place of the partition on sda. We create the first RAID device with:
mdadm --create /dev/md0 --chunk=64 --level=1 --raid-devices=2 missing /dev/sdb1
And we create the rest of the RAID devices:
mdadm --create /dev/md1 --chunk=64 --level=1 --raid-devices=2 missing /dev/sdb5 mdadm --create /dev/md2 --chunk=64 --level=1 --raid-devices=2 missing /dev/sdb6 mdadm --create /dev/md3 --chunk=64 --level=1 --raid-devices=2 missing /dev/sdb7 mdadm --create /dev/md4 --chunk=64 --level=1 --raid-devices=2 missing /dev/sdb8 mdadm --create /dev/md5 --chunk=64 --level=1 --raid-devices=2 missing /dev/sdb9
Type ‘cat /proc/mdstat‘ to see the 5 failed RAID devices:
# cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md5 : active (auto-read-only) raid1 sdb9[1] 1452590968 blocks super 1.2 [2/1] [_U] md4 : active (auto-read-only) raid1 sdb8[1] 389108 blocks super 1.2 [2/1] [_U] md3 : active (auto-read-only) raid1 sdb7[1] 3021812 blocks super 1.2 [2/1] [_U] md2 : active (auto-read-only) raid1 sdb6[1] 2927604 blocks super 1.2 [2/1] [_U] md1 : active (auto-read-only) raid1 sdb5[1] 5857268 blocks super 1.2 [2/1] [_U] md0 : active (auto-read-only) raid1 sdb1[1] 340980 blocks super 1.2 [2/1] [_U] unused devices:
Format, Mount and copy RAID devices
Prepare and copy the root partition (md0 mounted on /mnt)
mkfs.ext3 /dev/md0 mount /dev/md0 /mnt cd / && find . -xdev | cpio -pm /mnt
Prepare and copy /usr partition (md1 mounted on /mnt/usr)
mkfs.ext3 /dev/md1 mount /dev/md1 /mnt/usr cd /usr && find . -xdev | cpio -pm /mnt/usr
Prepare and copy /var partition (md2 mounted on /mnt/var)
mkfs.ext3 /dev/md2 mount /dev/md2 /mnt/var cd /var && find . -xdev | cpio -pm /mnt/var
Prepare swap partition (md3)
mkswap /dev/md3
Prepare /tmp partition (md4 mounted on /mnt/tmp)
mkfs.ext3 /dev/md4 mount /dev/md4 /mnt/tmp chmod 777 /mnt/tmp
Prepare /home partition (md5 mounted on /mnt/home)
mkfs.ext4 /dev/md5 mount /dev/md5 /mnt/home cd /home && find . -xdev | cpio -pm /mnt/home
Change fstab
Edit /mnt/etc/fstab and change all devices according to the new RAID devices My /mnt/etc/fstab looks like this now
# <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc defaults 0 0 # / was on /dev/sda1 during installation /dev/md0 / ext3 errors=remount-ro 0 1 # /home was on /dev/sda9 during installation /dev/md5 /home ext4 defaults 0 2 # /tmp was on /dev/sda8 during installation /dev/md4 /tmp ext3 defaults 0 2 # /usr was on /dev/sda5 during installation /dev/md1 /usr ext3 defaults 0 2 # /var was on /dev/sda6 during installation /dev/md2 /var ext3 defaults 0 2 # swap was on /dev/sda7 during installation /dev/md3 none swap sw 0 0 /dev/scd0 /media/cdrom0 udf,iso9660 user,noauto 0 0
Edit /boot/grub/grub.cfg and change root= so it points to /dev/md0.
Reboot on RAID devices
This worked the first time for me, without any console access :) Run update-grub when you are logged in again.
Fix paritions types on sda
Now that we don’t use the partitions on our original system disk (sda) we can edit the partition table and set the partitions to type ‘
fd raid autodetect‘. My sda partition table looks like this now:
Device Boot Start End Blocks Id System /dev/sda1 * 1 43 340992 fd Linux raid autodetect /dev/sda2 43 182402 1464795137 5 Extended /dev/sda5 43 773 5858304 fd Linux raid autodetect /dev/sda6 773 1137 2928640 fd Linux raid autodetect /dev/sda7 1137 1514 3022848 fd Linux raid autodetect /dev/sda8 1514 1562 389120 fd Linux raid autodetect /dev/sda9 1562 182402 1452592128 fd Linux raid autodetect`
Add sda partitions to RAID devices
Now it’s time to add the unused partitions from sda to our failed raid devices.
mdadm --add /dev/md0 /dev/sda1
We can see the RAID device (md0) rebuilding onto the new disk with ‘cat /proc/mdstat‘ Add the other partitions:
mdadm --add /dev/md1 /dev/sda5 mdadm --add /dev/md2 /dev/sda6 mdadm --add /dev/md3 /dev/sda7 mdadm --add /dev/md4 /dev/sda8 madam --add /dev/md5 /dev/sda9
To watch the rebuild, run watch cat /proc/mdstat
Every 2,0s: cat /proc/mdstat Mon Dec 6 19:55:04 2010 Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid1 sda1[2] sdb1[1] 340980 blocks super 1.2 [2/2] [UU] md1 : active raid1 sda5[2] sdb5[1] 5857268 blocks super 1.2 [2/2] [UU] md2 : active raid1 sda6[2] sdb6[1] 2927604 blocks super 1.2 [2/1] [_U] resync=DELAYED md3 : active raid1 sda7[2] sdb7[1] 3021812 blocks super 1.2 [2/1] [_U] resync=DELAYED md4 : active raid1 sda8[2] sdb8[1] 389108 blocks super 1.2 [2/1] [_U] resync=DELAYED md5 : active raid1 sda9[2] sdb9[1] 1452590968 blocks super 1.2 [2/1] [_U] [>....................] recovery = 0.6% (9617600/1452590968) finish=268.3min speed=89629K/sec unused devices:
Don’t reboot until all devices has rebuilt.