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
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