Install Woody On RAID1

Introduction

This describes how to install Debian Woody on a RAID-1 system (mirrored disks), with RAID being implemented in the kernel rather than in a dedicated RAID controller. Note that some knowledge of RAID1 under Linux is assumed.

What you will need

• A system with two hard disks. Ideally these disks will be on separate controllers if they are IDE disks; this is for performance reasons. Also ideally the disks will be identical, although again this is not strictly necessary. If the disks are not identical then do the initial installation on the smaller disk.
• A Debian installation CD
• Some Linux experience. By that, I mean that this document is not aimed at someone carrying out his or her first ever Linux installation. I make assumptions (eg, that you can edit files and partition disks), but, that said, if you do have questions then I suggest you ask on the mailing list where I or others will try to help.

A note on BIOS settings

If you have identical disks, try to ensure that the system BIOS is set such that Linux sees both disks with the same cylinder/head/sector readings. This can be checked by booting the Debian installation CD and running cfdisk on each disk, and noting how it reports the C/H/S settings. If they do differ for identical disks, try changing the disk mapping in the BIOS (Normal addressing or possibly CHS seem to work best). Sometimes zeroing the first few blocks of both disks (dd if=/dev/zero of=/dev/hda bs=512 count=10000f) can help.

Assumptions

Your system has /dev/hda and /dev/hdc, and they are identical drives (and the geometry is reported as such by the BIOS). If you are using different devices (eg, /dev/sda and /dev/sdb) then just substitute appropriately.

HOWTO!

1. Boot the Debian installation CD and proceed as usual to disk partitioning and partition /dev/hda. You will need at least two partitions of a size large enough to hold a Debian base installation. Personally, I usually use drives of at least 80Gb, and I partition them as follows:

 /dev/hda1 - / - 5Gb  /dev/hda2 - swap - 512Mb  /dev/hda3 - /tmp - 1Gb  /dev/hda5 - /var - 10Gb  /dev/hda6 - /home - remainder

You can, of course, use smaller partitions, but for the purposes of this HOWTO I’m going to assume that you have the above partitioning scheme, and that both / (root) and /home are at least 1Gb in size.

The filesystem used is not important, but ensure that all partitions on /dev/hda have valid filesystems or swap signatures. The partition types should be 0x83 except for the swap partition, which should be 0x82.

2. When mounting the root partition for the installation, use a partition other than /dev/hda1. In this HOWTO I will use /dev/hda5. At this point, do not specify any other partitions; rather, place the entire installation on /dev/hda5.

3. Continue the installation to completion, carry out the first reboot and configure the system. Do not install any additional packages yet. At this point you should have a minimal Debian system which differs from a normal system only in that it is installed in /dev/hda5 rather than the more traditional /dev/hda1.

4. The default Debian kernel include RAID modules, but if we are to boot from a RAID1 parition we will need to have the RAID1 drivers built in to the kernel, and thus the kernel needs to be rebuilt. If you need help with this, I suggest following the instructions at http://www.debian.org/doc/manuals/reference/ch-kernel.en.html#s-kernel-debian and at LinuxHints/KernelCompiling, but note that you will need to install initrd-tools in addition to the packages mentioned there. The only change you must make to the kernel configuration file is under the section “Multi-device support (RAID and LVM)”, where you must change both “RAID support” and “RAID-1 (mirroring) mode” from modules (“<M>”) to built-in (“<*>”). Rebuild and install the kernel, and reboot.

  * Note: Since this is from a base install you will also need to install 'build-essential' which is  not mentioned on the linked page (pretty much  assumed really!). When it is not installed  the error doesn't specifically request it, but if you read the output from the make  command you see the real cause.

5. Change all partition types on the boot disk to 0xfd, regardless of filesystem used (including the swap partition)

6. Create partitions on /dev/hdc. If the disks are identical, check that the kernel sees them that way too by comparing the output of sfdisk -g /dev/hda and sfdisk -g /dev/hdc. If the kernel does see them as identical then the partition layout can be copied from /dev/hda to /dev/hdc with:

  sfdisk -d /dev/hda | sfdisk /dev/hdc    If the disks are not identical, manually create the partitions on `/dev/hdc` (as type `0xfd`). They must correspond to the partitions on `/dev/hda`, and must not be smaller than the corresponding partition on /dev/hda.

7. Install raidtools2: apt-get install raidtools2

8. Create /etc/raidtab – see raidtab(5). Mine is shown below, and the format should be reasonably intuitive:

 # /  raiddev                /dev/md0  raid-level             1  nr-raid-disks          2  chunk-size             32  persistent-superblock  1  device                 /dev/hda1  raid-disk              0  device                 /dev/hdc1  raid-disk              1

 # swap  raiddev                /dev/md1  raid-level             1  nr-raid-disks          2  chunk-size             32  persistent-superblock  1  device                 /dev/hda2  raid-disk              0  device                 /dev/hdc2  raid-disk              1

 # /tmp  raiddev                /dev/md2  raid-level             1  nr-raid-disks          2  chunk-size             32  persistent-superblock  1  device                 /dev/hda3  raid-disk              0  device                 /dev/hdc3  raid-disk              1

 # /var  raiddev                /dev/md3  raid-level             1  nr-raid-disks          2  chunk-size             32  persistent-superblock  1  device                 /dev/hda5  raid-disk              0  device                 /dev/hdc5  raid-disk              1

 # /home  raiddev                /dev/md4  raid-level             1  nr-raid-disks          2  chunk-size             32  persistent-superblock  1  device                 /dev/hda6  raid-disk              0  device                 /dev/hdc6  raid-disk              1

9. Create the /dev/md0 device with:

  '''`mkraid /dev/md0`'''    You may need to use the -f (`--force`) switch depending upon what filesystems may have been installed before. Once the command completes, check the state of the RAID system with:

  cat /proc/mdstat    This should show you that `/dev/md0` is active, and probably resyncing.

10. Create the required filesystem on /dev/md0 (for example, mke2fs -j /dev/md0 for an ext3 filesystem).

11. Edit /etc/lilo.conf and change the root= line to root=/dev/md0 (leave the boot line as boot=/dev/hda).

12. Copy your one-partition Debian installation to /dev/md0:

  # mount /dev/md0 /mnt   # tar -C / -cvlf - . | tar -C /mnt -xf -

13. chroot to your new root parition and run lilo:

  # chroot /mnt   # lilo   # exit

14. Edit /mnt/etc/fstab and change the root device from /dev/hda5 to /dev/md0, and the swap device from /dev/hda2 to /dev/md1.

15. Check that the RAID disk has finished resyncing (with cat /proc/mdstat)

16. Unmount /dev/md0 and stop RAID:

  # umount /dev/md0   # raidstop /dev/md0    17. Reboot

You should now have a system running on /dev/md0 (check with df and also with cat /proc/mdstat).

Things to do next:

• Create /dev/mdx devices for your other partitions, and create filesystems on them

• Move, for example, /home from the root partition to its own partition, possibly using a variation of the tar command used earlier

• Put some monitoring in place to check and report on the health of the RAID system (no point in having it if you don’t know when one of the disks has problems)

• Beef up the boot support (install lilo-doc and read /usr/share/doc/lilo-doc/README.raid1.gz)

KeithEdmunds, July 2004