Installing Arch on a RAID (for dummies)

Question

Playing with RAID's is fun for all the family, and makes things go faster.
this is how I (re)installed Arch Linux, in a simple RAID configuration.
Ingredients
===========
1. Two 160GB drives
2. Arch Linux CD (Dont Panic)
Planning
========
1. root partition on a RAID 1 setup (mirroring)
2. home partition on a RAID 0 setup (striping)
3. swap partition on a RAID 0 setup (striping)
in this kinda setup, one disk can fry, but the system will still boot and function normally.
home will be lost for ever, but I always back it up anyway (and so should you).
*Important* - make sure your two IDE drives are not connected to the same cable, setup one as a primary master and the second as a secondary master.
The works
=========
1. Boot the machine using the setup CD.
2. Using cfdisk, partition the two drives exactly the same:
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        4863    39062016   83  Linux
/dev/sda2            4864       17021    97659135   83  Linux
/dev/sda3           17022       17083      498015   82  Linux swap / Solaris
I chose 40GB for root, 100GB for home (results in 200GB), and 1GB for swap.
Do exactly the same on the second drive /dev/sdb
3. create the RAIDs using mdadm:
modprob raid1
modprob raid0
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1
mdadm --create /dev/md1 --level=0 --raid-devices=2 /dev/sda2 /dev/sdb2
mdadm --create /dev/md2 --level=0 --raid-devices=2 /dev/sda3 /dev/sdb3
4. create filesystems on the partitions:
mkfs.xfs /dev/md0
mkfs.xfs /dev/md1
mkswap /dev/md2
5. mount the root partition on /mnt
mount /dev/md0 /mnt
6. start the setup program
/arch/setup
7. select all base packages
8. install packages
9. configure:
choose configure system and then, edit mkinitcpio.conf modules section:
MODULES="ata_generic ata_piix raid1 raid0 xfs"
In this line, I only added "raid1 raid0 xfs" to the modules.
then, edit mkinitcpio.conf hooks section, and add the RAID stuff after that:
HOOKS="base udev raid autodetect pata scsi sata usbinput keymap filesystems"
md=0,/dev/sda1,/dev/sdb1
md=1,/dev/sda2,/dev/sdb2
md=2,/dev/sda3,/dev/sdb3
In the hooks line, I have added the raid hook before autodetect
10. install the kernel
choose install kernel from the menu.
11. Install grub
choose install bootloader then grub
edit the grub entry to:
# (0) Arch Linux
title  Arch Linux  [/boot/vmlinuz26]
root   (hd0,0)
kernel /boot/vmlinuz26 root=/dev/md0 ro md=0,/dev/sda1,/dev/sdb1
initrd /boot/kernel26.img
install grub to /dev/sda
when prompted about root partition choose /dev/sda1
when prompted about RAID stuff choose no
do exactly the same on /dev/sdb
12. exit the setup program
13. fix mdadm.conf
mdadm -D --scan >>/mnt/etc/mdadm.conf
14. fix fstab
add this to /mnt/etc/fstab:
/dev/md0                /       xfs     defaults                0       0
/dev/md1                /home   xfs     defaults                0       0
/dev/md2                swap    swap    defaults                0       0
15. reboot and install the rest of the system
16. make sure all is well:
cat /proc/mdstat
Personalities : [raid1] [raid0] [linear] [multipath] [raid6] [raid5] [raid4] [raid10]
md2 : active raid0 sda3[0] sdb3[1]
      995840 blocks 64k chunks
md1 : active raid0 sda2[0] sdb2[1]
      195318016 blocks 64k chunks
md0 : active raid1 sdb1[1] sda1[0]
      39061952 blocks [2/2] [UU]
mount
/dev/md0 on / type xfs (rw)
/dev/md1 on /home type xfs (rw)
make sure swap is on:
cat /proc/swaps
Filename                                Type            Size    Used    Priority
/dev/md2                                partition       995832  0       -1
17. If things go wrong, you can reassemble the RAIDs after booting from the setup CD, dont recreate them:
mdadm --reassemble /dev/md0 /dev/sda1 /dev/sdb1
for more reading, consult the WIKI: http://wiki.archlinux.org/index.php/Ins … AID_or_LVM
Last edited by daf666 (2008-03-08 20:36:42)

Answer 1

Sorry for the late reply clickit, I guess you might have fixed it already.
There is a mistake in the guide, I will correct it now, the types in these lines should be --level=0
mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sda2 /dev/sdb2
mdadm --create /dev/md2 --level=1 --raid-devices=2 /dev/sda3 /dev/sdb3
Very sorry about that, but that does not cause your problem, because it would have created a mirror RAID instaed of a stripe.
Your BIOS has nothing to do with the Linux software RAID, the RAID settings you see in BIOS are probably to enable the on-board RAID controller you have.
The grub part is tricky, you have to make sure whats in the configuration file is according to the setup that you have (not just copy from the guide).
Also keep in mind that if you have SATA, things might look different and the setup might need to be different.
PS - regarding swap, since I wrote the guide I removed the swap space and instead I use a swap file on the RAID0.. I guess it the same because my system  rarely uses swap anyway
Last edited by daf666 (2007-10-17 21:31:59)