Recipe for Mirrored OS Drives

A few weeks ago, I promised that I would put my "recipe" here for creating "mirrored OS drives from an existing OS Drive". This "recipe" combines what I learned from MANY OTHER sometimes conflicting documents on the same subject -- documents that were probably developed for earlier kernels and distributions.

I tried to follow the other instructions and always found that some steps didn't work for me or weren't necessary, or that some important steps were missing. I hope my recipe helps others who are trying to create mirrored drives with their recent Linux distributions.

Please keep in mind the following:

1) 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.

2) 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.

3) If you have IDE drives instead of SATA drives, you should substitute "/dev/hdX" where I have "/dev/sdX"

4) Many other instructions that I read claimed that it was 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.

5) 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.

6) 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.

Recipe for Creating Mirrored OS Drives from Exiting OS Drive

REQUIREMENTS:

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

CAUTION:

-- 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 WANT TO SWITCH FROM IDE TO SATA:

If you normally boot off of 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.

THE PROCEDURE

-- 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 /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 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

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

       /dev/md0 /
       /dev/md2  /home
       cdrom
       proc
       /dev/md1 swap

-- 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"

OR

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:

auto=yes

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-2.6.16.20.img 2.6.16.20

Substitute YOUR EXACT KERNEL for 2.6.16.20 (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 arrays 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-2.6.16.20-es1.img
2.6.16.20-es1

-- run lilo

/sbin/lilo

-- exit chroot environment

exit

-- 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

Feel free to add it here:
http://linux-raid.osdl.org/index.php/Main_Page

I haven't been able to do much for a few weeks (typical - I find some time and use it all up just getting the basic setup done - still it's started!)

David

Any hints on how to add a page?

Andy

Yep :)

First off it would help to read up on Wikis :
http://meta.wikimedia.org/wiki/Help:Contents

Basically you:
* go to the page where you want to link from
* edit that page to link to your new (not yet created) page
* save your edit
* click on the (red) link and you'll be given a page to edit
* type...

I suggest you link from http://linux-raid.osdl.org/index.php/RAID_Boot

David

On 2 Oct 2006, David Greaves spake:

The pages don't really have the same purpose. RAID_Boot is how to boot your RAID system using initramfs'; this is how to set up a RAID system in the first place', i.e., setup.

I'll give it a bit of a tweak-and-rename in a bit.

`In typical emacs fashion, it is both absurdly ornate and
 still not really what one wanted.' --- jdev

Fair :)

FYI I've done quite a bit on the Howto section:
http://linux-raid.osdl.org/index.php/Overview

It still needs a lot of work I think but it's getting there...

David

On Tue, 03 Oct 2006, David Greaves prattled cheerily:

Ka wow.

Yeah: the `booting on RAID' and RAID_Boot could be merged, and it certainly could do with a refactor and update.

But it's a *lot* better than having it rotting in a HOWTO.

I'll look at it shortly.

`In typical emacs fashion, it is both absurdly ornate and
 still not really what one wanted.' --- jdev

At least add the -H flag to copy hardlinks. -S for sparse files might also be useful.

Erik

+-- Erik Mouw -- www.harddisk-recovery.com -- +31 70 370 12 90 --
| Lab address: Delftechpark 26, 2628 XH, Delft, The Netherlands