[CentOS] Turning root partition into a RAID array
Peter Farrow
peter at farrows.org
Tue Nov 15 15:56:51 UTC 2005
Once you've mdadm and done you're other stuff you can use grub, to
install a boot loader on each disk, if you are using grub...
You might find this excerpt useful:
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From: Michael Martucci <m.martucci at gmx.net>
To : <linuxsa at linuxsa.org.au>
Date: Tue, 29 Jul 2003 14:44:46 +0930
GRUB + RAID howto
In the Software RAID howto it is mentioned that it is not known how
to set up GRUB to boot off RAID. Here is how I did it:
**Follow at your own risk. If you break something it's your fault.**
==================================================================
Configuration:
- /dev/hda (Pri. Master) 60 GB Seagate HDD (blank)
- /dev/hdc (Sec. Master) 60 GB Seagate HDD (blank)
- /dev/hdd (Sec. Slave) CDROM Drive
Setup Goals:
- /boot as /dev/md0: RAID1 of /dev/hda1 & /dev/hdc1 for redundancy
- / as /dev/md1: RAID1 of /dev/hda2 & /dev/hdc2 for redundancy
- swap*2 with equal priority: /dev/hda3 & /dev/hdc3 for more speed
- GRUB installed in boot records of /dev/hda and /dev/hdc so either
drive can fail but system still boot.
Tools:
- mdadm (http://www.cse.unsw.edu.au/~neilb/source/mdadm/)
(I used 1.2.0, but notice that as of 20030729 1.3.0 is available)
1. Boot up off rescue/installation CD/disk/HDD/whatever with mdadm
tools installed.
2. Partitioning of hard drives:
(I won't show you how to do this. See: # man fdisk ; man sfdisk )
But here's how stuff was arranged:
------------------------------------------------------------------
# sfdisk -l /dev/hda
Disk /dev/hda: 7297 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting
from 0
Device Boot Start End #cyls #blocks Id System
/dev/hda1 * 0+ 16 17- 136521 fd Linux raid autodetect
/dev/hda2 17 7219 7203 57858097+ fd Linux raid autodetect
/dev/hda3 7220 7296 77 618502+ 82 Linux swap
/dev/hda4 0 - 0 0 0 Empty
------------------------------------------------------------------
To make /dev/hdc the same:
------------------------------------------------------------------
# sfdisk -d /dev/hda | sfdisk /dev/hdc
------------------------------------------------------------------
/dev/hd[ac]1 for /dev/md0 for /boot
/dev/hd[ac]2 for /dev/md1 for /
/dev/hd[ac]3 for 2*swap
It is important to make md-to-be partitions with ID 0xFD, not 0x83.
3. Set up md devices: (both are RAID1 [mirrors])
------------------------------------------------------------------
# mdadm --create /dev/md0 --level=1 \
--raid-devices=2 /dev/hda1 /dev/hdc1
# mdadm --create /dev/md1 --level=1 \
--raid-devices=2 /dev/hda2 /dev/hdc2
------------------------------------------------------------------
4. Make filesystems:
------------------------------------------------------------------
# mke2fs /dev/md0
# mkreiserfs /dev/md1
# mkswap /dev/hda3
# mkswap /dev/hdc3
------------------------------------------------------------------
5. Install Your distribution:
Simply treat /dev/md0 and /dev/md1 as the partitions to install on,
and install the way your normally do. Eg, for Gentoo:
------------------------------------------------------------------
# mkdir newinst
# mount -t reiserfs /dev/md1 ./newinst
# cd newinst
# mkdir boot
# mount -t ext2 /dev/md0 ./boot
# tar -xvjpf ../stage1-x86-1.4_rc2.tbz2
# mount -o bind /proc ./proc
# chroot ./
...
------------------------------------------------------------------
Here're the relevant entries /etc/fstab for the newly created
partitions:
------------------------------------------------------------------
/dev/md0 /boot ext2 noauto,noatime 1 1
/dev/md1 / reiserfs noatime 1 1
/dev/hda3 none swap sw,pri=1 0 0
/dev/hdc3 none swap sw,pri=1 0 0
------------------------------------------------------------------
The "pri=1" for each of the swap partitions makes them the same
priority so the kernel does striping and that speeds up vm. Of
course, this means that if a disk dies then the system may crash,
needing a reboot. Perhaps it would be wiser to make hd[ac]3 a RAID1
array too, and just use /dev/md2 as swap.
6. Setting up GRUB: (assuming you've already installed it)
------------------------------------------------------------------
# grub
grub> root (hd0,0)
Filesystem type is ext2fs, partition type 0xfd
grub> setup (hd0)
Checking if "/boot/grub/stage1" exists... yes
Checking if "/boot/grub/stage2" exists... yes
Checking if "/boot/grub/e2fs_stage1_5" exists... yes
Running "embed /boot/grub/e2fs_stage1_5 (hd0)"... 16 sectors are
embedded.
succeeded
Running "install /boot/grub/stage1 (hd0) (hd0)1+16 p
(hd0,0)/boot/grub/stage2 /boot/grub/grub.conf"... succeeded
Done.
grub> root (hd1,0)
Filesystem type is ext2fs, partition type 0xfd
grub> setup (hd1)
Checking if "/boot/grub/stage1" exists... yes
Checking if "/boot/grub/stage2" exists... yes
Checking if "/boot/grub/e2fs_stage1_5" exists... yes
Running "embed /boot/grub/e2fs_stage1_5 (hd1)"... 16 sectors are
embedded.
succeeded
Running "install /boot/grub/stage1 (hd1) (hd1)1+16 p
(hd1,0)/boot/grub/stage2 /boot/grub/grub.conf"... succeeded
Done.
grub> quit
------------------------------------------------------------------
Here is how /boot/grub/grub.conf is: (/dev/md0 mounted as /boot)
(Assuming kernel is installed as /boot/bzImage, and RAID1 support
compiled into the kernel).
------------------------------------------------------------------
# Boot automatically after 30 secs.
timeout 30
# By default, boot the first entry.
default 0
# Fallback to the second entry.
fallback 1
# For booting with disc 0 kernel
title GNU/Linux (hd0,0)
kernel (hd0,0)/bzImage root=/dev/md1
# For booting with disc 1 kernel, if (hd0,0)/bzImage is unreadable
title GNU/Linux (hd1,0)
kernel (hd1,0)/bzImage root=/dev/md1
------------------------------------------------------------------
Now you should be able to reboot your system and play!
==================================================================
Please let me know of any errors, feedback, etc.
Michael Martucci.
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Nigel kendrick wrote:
>I have a CentOS 4.2 system that was set up VERY quickly following the demise
>of its former life as a CentOS 3 server - you don't want the full story, but
>it had to be done quickly to get a company up and working following a slight
>disaster involving an electrician, a portable appliance safety tester and a
>pulled power cable - anyway, here's where I am at...
>
>Everything is running fine but I now want to mirror the root partition
>(/dev/hda3). I have read quite a few set of notes on the theory but since
>they contain conflicting advice I am hoping someone here can set me straight
>- here's what IO want to do:
>
>hda3 and hde3 become a mirrored pair (/dev/md0) and this is mounted at boot
>time as /
>
>Is it as simple as a quick mdadm command and then an edit of /etc/inittab??
>
>If I try and use mdadm right now I get complaints that /dev/hda3 is busy
>(fair enough) so I guess I need to be in less than 'full steam ahead' mode
>to make the change - over to you....
>
>Thanks
>
>_______________________________________________
>CentOS mailing list
>CentOS at centos.org
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