SATA RAID Boot Recipe

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Recipe for Creating Mirrored OS Drives from Existing OS Drive

Please keep in mind the following:

  • This recipe works with recent 2.6.x kernels and recent Linux distributions that use UDEV. Older distributions that rely on DEVFS and that include older versions of mdadm probably will require some variations in the steps. I tested this with Mandriva 2006 and a 2.6.16 kernel.
  • This recipe is designed for SATA drives and a motherboard with SATA controllers that are supported by the current Linux kernels. It might not work with all motherboards.
  • If you have IDE drives instead of SATA drives, you should substitute /dev/hdX where I have /dev/sdX.
  • Many other instructions that you can find on the Web claim that it is necessary to create a separate boot partition in order to boot with mirrored drives. I found that I was able to create mirrored OS drives WITHOUT a separate boot partition. FYI -- my installation has three partitions -- the "root" partition "/" as well as a partition for "swap" and "home". You may have a different layout. Just go with the layout to which you are accustomed. It should work.
  • This recipe does NOT require compiling RAID drivers or other drivers into the kernel. It uses an "initial ramdisk" (initrd) to load the required drivers during the early stages of booting up.
  • The distribution YOU use may have some important differences from Mandriva 2006. For instance, Mandriva puts the mdadm.conf in /etc/ and some other distributions put it in /etc/mdadm/. In addition, Mandriva doesn't require editing any sort of "initrd.conf" file in order to build a proper initrd so that it includes the required drivers. Your distribution may require you to specify what you want to put in the initrd.


  • One or Two NEW SATA drives of the same size. If you only supply ONE new drive, you must have an existing SATA drive of the SAME size that you can use as the other part of your mirrored pairs.
  • A Live CD/DVD Linux Distribution such as Mandriva One or Knoppix


  • It is probably best to have two NEW SATA drives in addition to an existing SATA OS drive. However, if you decide to use your existing SATA drive as one of your RAID drives, you should back up your existing OS drive. That way, if you make a mistake, you can always put the current SATA OS drive back in your system.

For Backup, I highly recommend using Acronis True Image. It's a great, fast, and relatively inexpensive imaging product that allows you to copy your existing OS image from one disk and restore it to another.


If you normally boot off an IDE drive but want to switch to SATA, you can use Acronis True Image make an image from your IDE drive and then restore it to a SATA drive. Then, you only need to edit your /etc/fstab and boot loader configuration file (i.e., /etc/lilo.conf) so that they refer to /dev/sdX instead of /dev/hdX.


  • Assuming you already boot from a SATA drive, install a second SATA drive. If you are going to use both drives as members of your mirrored pairs, the NEW drive should be the same size or larger than the first drive.
  • Boot your computer as you normally do from the SATA drive.
  • Assuming that your existing OS drive comes up as /dev/sda and that the new drive comes up as /dev/sdb, copy the partition layout from /dev/sda to /dev/sdb so that you have identical partition layouts on each disk:
           sfdisk -d /dev/sda | sfdisk /dev/sdb
  • Set the partition type on all /dev/sdb partitions to "raid autodetect -- type fd", except on any EXTENDED PARTITION. For example, assuming your root (/) partition is currently on /dev/sda1, and you have an extended partition on 2, and two logical partitions (swap and home) on 5 and 6:
           fdisk /dev/sdb
           ENTER "t"
           SELECT "1" for partition 1
           ENTER "fd" for partition type
           Repeat for partitions 5 and 6
  • Shutdown your computer
  • Reboot using a Live CD/DVD distribution (i.e., Mandriva One, or Knoppix)
  • Open a terminal (i.e., KDE's Konsole) and become root.
  • Create "degraded mirrored RAIDS" on /dev/sdb1, /dev/sdb5, /dev/sdb6 (or on ALL partitions that are part of your OS drive and that you want to mirror). The basic idea is that your motherboard probably only has built-in support for two SATA drives. In order to copy your existing OS from the current standalone SATA drive to the mirrored drives, you have to create the mirrors such that they are initially MISSING their second parts. You will add the second parts latter after you copy everything from the standalone SATA OS drive.
       mdadm -Cv -ayes /dev/md0 -n2 -l1 missing /dev/sdb1
       mdadm -Cv -ayes /dev/md1 -n2 -l1 missing /dev/sdb5
       mdadm -Cv -ayes /dev/md2 -n2 -l1 missing /dev/sdb6
  • Confirm that the RAIDS are running:
       cat /proc/mdstat

You should see that each RAID is listed as "_U"

  • Format the md devices. For example:
       mkfs.ext3 /dev/md0
       mkswap /dev/md1
       mkfs.ext3 /dev/md2
  • Make mountpoints for old and new partitions. This assumes your "Live Distro" allows you to create new mountpoints inside /mnt.
        mkdir /mnt/oldroot
        mkdir /mnt/oldhome
        mkdir /mnt/newroot
        mkdir /mnt/newhome
  • Mount partitions from /dev/sdaX (the original OS drive) and from the NEW /dev/md devices (the "degraded" md devices you just created above).
        mount -t ext3 /dev/sda1 /mnt/oldroot
        mount -t ext3 /dev/sda5 /mnt/oldhome
        mount -t ext3 /dev/md0 /mnt/newroot
        mount -t ext3 /dev/md2 /mnt/newhome
  • Run rsync to copy contents from your existing OS drive
        rsync -av /mnt/oldroot /mnt/newroot
        rsync -av /mnt/oldhome /mnt/newhome

NOTE: Running rsync from your Live Distro will avoid copying over any unwanted files from /proc or /sys or any "lock files" or "PID" files that SHOULD NOT be copied.

-- edit fstab on /mnt/newroot/etc/fstab so that you will be mounting mdX devices and not sdX devices. You can use an editor such as "vim" or "emacs". For example:

   vim /mnt/newroot/etc/fstab

Make sure the "/", "swap" and "home" partitions refer to "/dev/mdX" instead of "/dev/sdX"

       /dev/md0 / ext3 defaults 1 1
       /dev/md2  /home ext3 defaults 1 2
       /dev/hdc /mnt/cdrom iso9660 ro,noauto,user,exec 0 0
       none /proc proc defaults 0 0
       /dev/md1 swap swap defaults 0 0

  • edit lilo.conf (if you use the LILO bootloader). If you use GRUB, you'll have to figure out what to do in YOUR case.
       vim /mnt/newroot/etc/lilo.conf
       Set "boot=/dev/md0"  (no quotes)
       Add line to lilo.conf main section that says:
             "raid-extra-boot=/dev/sda,/dev/sdb"  (no quotes)
       change root=/dev/md0 on all kernels
       change resume=/dev/md1 on all kernels  (assuming your swap
       partition is /dev/md1
  • If you were planning to remove your existing OS drive and replace it with a new drive, SHUTDOWN NOW. Remove the original SATA OS drive. Replace it with a NEW SATA drive (same size as the other one you installed at the beginning). Then reboot again with your LIVE Distro and skip down TWO steps to where it says "copy partition layout from /dev/sdb to /dev/sda"


If you plan on using your existing OS drive as part of your mirrored OS drive, follow the next two instructions

  • Unmount /dev/sda partitions. You may need to close your Terminal window and open it again so that it doesn't tell you the partitions are "busy"
       umount /mnt/oldroot
       umount /mnt/oldhome

Delete partitions on /dev/sda

       fdisk /dev/sda
       SELECT "d" for "delete"
       SELECT "6" for "partition 6"
       SELECT "d" for "delete"
       SELECT "5" for "partition 5"
       SELECT "d" for "delete"
       SELECT "2" for "partition 2"
       SELECT "d" for "delete"
       SELECT "1" for "partition 1"
  • copy partition layout from /dev/sdb to /dev/sda
       sfdisk -d /dev/sdb | sfdisk /dev/sda

  • add partitions from /dev/sda to each "degraded" md device (which currently only consist of partitions from /dev/sdb.
       mdadm /dev/md0 -a /dev/sda1
       mdadm /dev/md1 -a /dev/sda5
       mdadm /dev/md2 -a /dev/sda6
  • Check resyncing progress with
       cat /proc/mdstat
  • WHEN resyncing is done, copy your running RAID configuration to mdadm.conf. To do that,

as root type:

       mdadm --detail --scan >> /mnt/newroot/etc/mdadm.conf
  • Edit your new /mnt/newroot/etc/mdadm.conf file. This file will need TWO extra instructions in order to start the RAIDS automatically on booting. Open the file with a text editor. For example:
       vim /mnt/newroot/etc.mdadm.conf

At at top of mdadm.conf, add:

       DEVICE /dev/sda1 /dev/sda5 /dev/sda6 /dev/sdb1 /dev/sdb5 /dev/sdb6

(Note: be sure to include any OTHER partitions that are part of your RAID 1 mirrored pairs. For example, if you have a separate partition for /usr you might need to add another listing. If your drives are NOT sda and sdb, use the correct device letters

Next, at the end of each ARRAY statement add:


The above option, "auto=yes" is required if you are running under UDEV so that mdadm will recreate the device nodes /dev/md1 and /dev/md2 EACH time you boot. Leave a space before "auto" and the UUID number.

  • chroot to /mnt/newroot
       chroot /mnt/newroot
  • run mkinitrd. For example:
       /sbin/mkinitrd -v /boot/initrd-

Substitute YOUR EXACT KERNEL for (which is the kernel I am running)

In MY case I also had to tell mkinitrd NOT to worry about a 3ware driver (3w_9xxx) that I use for my storage array because it wasn't finding it. I think that's because there's an inconsistency between the name of the 3ware driver (with an underscore "_") and the name of the driver file 3w-9xxx.ko (with a dash "-"). Having a "--builtin" statement (see below) tells mkinitrd that the driver is built into the kernel so not to worry about putting the module into the initrd. In my case, the driver is NOT built into the kernel, but I don't need the driver to be present early in the boot process so it's okay to load it later.

   /sbin/mkinitrd -v --builtin=3w_9xxx /boot/initrd-

  • run lilo
  • exit chroot environment
  • unmount RAIDS
       umount /dev/md0
       umount /dev/md1
       umount /dev/md2
  • stop RAIDS
       mdadm --stop /dev/md2
       mdadm --stop /dev/md1
       mdadm --stop /dev/md0

NOTE: I perform the above two steps because I have seen various Live CDs crash or freeze on exit and I want to be sure I have cleanly unmounted and stopped my RAIDs before rebooting.

  • reboot without Live CD to be sure everything is working. Your MIRRORED OS DRIVE should now boot.

I hope that works for you. Please feel free to pass these instructions along to other.

Andy Liebman

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