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Installing Debian with SATA based RAID

Late breaking news (4/05)

The newer Debian installers have Raid (and also LVM) working, so this guide should not be needed unless you are transitioning from a standard set up to raid without reinstalling. It might also be helpful if you are debugging a broken raid.

Now for 2.6 kernel version

I've read that there will soon be an installer that will do raid installs and  perhaps even support SATA, but today it is manual.  My install on a Intel D865PERL mother board got 'interesting'.  The last Debian (beta 4) testing installer does support SATA as does a version of Debian/Libranet, but going on to RAID is a manual task.

The basic idea was to Install all on one drive, then partition the second drive with just the same sizes. Install mdadm (the new and improved replacement for raidtools). I'm assuming we are using clean drives. If one re-uses previously used disks the superblocks must be zeroed (--zero-superblock option to mdadm) before adding the partitions to the array.

This guide was produced using a Tyan S2875 Moter board.

The whole mess is harder than it should be and I hope this page becomes the basis for someone's automating script (hint hint).

Overview of steps

• Install Debian on first drive (/dev/sda)
• Creating a degraded RAID1 array on disk 2 (/dev/sdb)
• Update initrd
• Copying the Debian installation over from disk 1 (sda to sdb)
• Fix fstab on /Dev/md2
• Add disk 1 to the degraded array to create final raid array
• Update initrd again
• Produce /etc/mdadm/mdadm.conf
• Setup the monitoring daemon

In this example Disk1 and disk2 are /dev/sda and /dev/sdb respectively.

 The partitions I used are:

/boot 200m
/swap 1Gig raid0
/ rest of drive

A note on raid systems and swap:
It is possible for a system to crash if the swap area drive fails. If this is not a concern you could also set it up as simple swap areas or as raid0 to improve performance. (Raid1 also provides faster reads as a side benefit, but there is the cost  slower writes - but swap tends to be read more times than  written so you might still come out ahead.)).

Install Debian on first drive

I used the following partitions

Device	Size	Id	Eventual mount point
/dev/sda1	200M	83	/boot/
/dev/sda5	1G	82	swap
/dev/sda6	100G	83	/

I'm assuming you know how to do the above by running fdisk from the install of your choice.

After installing:

#apt-get install wajig (you don't want to be without wajig - it makes apt and dpkg user friendly!! )
#wajig install mdadm
#wajig install rsync
#wajig install e3
#wajig install jfsutils
Update kernel to kernel-image-2.6.8-1-k7-smp 

Partition Drive2 with fdisk

Device	Size	Id	Eventual mount point
/dev/sdb1	200M	fd	/boot/
/dev/sdb5	1G	fd	swap
/dev/sdb6	100G	fd	/

Create the raid devices

# mdadm --create /dev/md0 --level 1 --raid-devices=2 missing /dev/sdb1

The above line is the long version of the next line just for reference. .

#mdadm -Cv /dev/md0 -l1 -n2 missing /dev/sdb1
#mdadm -Cv /dev/md1 -l1 -n2 missing /dev/sdb5
#mdadm -Cv /dev/md2 -l1 -n2 missing /dev/sdb6

This creates 3 degraded RAID1 devices (for /boot, swap, and /) consisting of a dummy drive "missing" (why was this so hard to figure out!)

Now, a cat of /proc/mdstat will show your degraded raid devices are up and running

#cat /proc/mdstat
Personalities : [raid1]
md1 : active raid1 sdb5[1]
      979840 blocks [2/1] [_U]

md0 : active raid1 sdb1[1]
      192640 blocks [2/1] [_U]

md2 : active raid1 sdb6[1]
      159661888 blocks [2/1] [_U]

unused devices: 

Note how one drive in all three cases is missing ("_") as opposed to 'Up and running' ("U").

Creating the file systems and Mount them

#mkfs.jfs /dev/md0
#mkfs.jfs /dev/md2
#mkswap /dev/md1
#mkdir /mntroot
#mkdir/mntboot
#mount /dev/md2 /mntroot
#mount /dev/md0 /mntboot

Fix up initrd

If you are using a SATA drive you pay attention!

edit /etc/mkinitrd/mkinitrd.conf and change:

    MODULES=most

to

###MODULES=most
MODULES=dep

and

ROOT=probe

to

###ROOT=probe
ROOT="/dev/md2 jfs"

This tells init to use what it takes to boot off of a raid device not the /dev/sda device currently used.

Now run

#mkinitrd -o /boot/initrd.img-2.6.8-1-k7-smp-md 2.6.8-1-k7-smp

Edit /boot/grub/menu.lst

Copy the old listing below and paste it below:

title Debian GNU/Linux, kernel 2.6.8-1-k7-smp
root (hd0,0)
kernel /vmlinuz-2.6.8 root=/dev/sda6 ro 
initrd /initrd.img-2.6.8
savedefault
boot

Now edit the new stanzas noting the changes in bold:

title Debian GNU/Linux, kernel 2.6.8-1-k7-smp-md Disk1
root (hd0,0)
kernel /vmlinuz-2.6.8 root=/dev/md2 ro 
initrd /initrd.img-2.6.8-1-k7-smp-md
savedefault
boot

Now make a copy of the New stanza you just made and make the changes in bold:

title Debian GNU/Linux, kernel 2.6.8-1-k7-smp-md disk2
root (hd1,0)
kernel /vmlinuz-2.6.8 root=/dev/md2 ro 
initrd /initrd.img-2.6.8-1-k7-smp-md
savedefault
boot

Producing /etc/mdadm/mdadm.conf

edit /etc/mdadm/mdadm.conf

The top line in this example should be

DEVICE /dev/sda* /dev/sdb*

Then run:

mdadm --detail --scan >> /etc/mdadm/mdadm.conf

This should produce a proper file

Copy over everything to the degraded raid

#rsync -auHxv --exclude=/proc/* --exclude=/sys/* --exclude=/boot/* --exclude=/mntboot --exclude=/mntroot/ /* /mntroot/
#mkdir /mntroot/proc /mntroot/boot /mntroot/sys 
#chmod 555 /mntroot/proc
#rsync -auHx   /boot/ /mntboot/

Make Changes in /mntroot/etc/fstab

Changes in bold

# /etc/fstab: static file system information.
#
#      
proc /proc proc defaults 0 0
/dev/md1 none swap sw 0 0
/dev/md0 /boot jfs defaults 0 2
/dev/md2 / jfs defaults,errors=remount-ro 0 1
/dev/hda /media/cdrom iso9660 ro,user,noauto 0 0
/dev/fd0 /media/floppy auto rw,user,noauto 0 0
/dev/hda /cdrom iso9660 ro,user,noauto 0 0

Reboot

If it won't work you should be able to boot off of the old grub listing

At this point the box should be running off the degraded RAID1 devices.on the second drive (/dev/sdb)

Check that everything works

If all is OK you should chnge the partition types of the first drive (/dev/sda) - but you will lose all data!!

Device	Size	Id	Eventual mount point
/dev/sda1	200M	fd	/boot/
/dev/sda5	1G	fd	swap
/dev/sda6	100G	fd	/

Attach the original drive's partitions to the existing (degraded) RAID arrays:

# mdadm /dev/md0 -a /dev/sda1
# mdadm /dev/md1 -a /dev/sda5
# mdadm /dev/md2 -a /dev/sda6

#cat /proc/mdstat

Personalities : [raid1]
md0 : active raid1 sda1[0] sdb1[1]
      192640 blocks [2/2] [UU]

md1 : active raid1 sda5[0] sdb5[1]
      979840 blocks [2/2] [UU]

md2 : active raid1 sda6[2] sdb6[1]
      159661888 blocks [2/1] [_U]
      [===>.................]  recovery = 17.9% (28697920/159661888) finish=56.4min speed=38656K/sec
unused devices: 

After a while all devices are in sync:

# cat /proc/mdstat

Personalities : [raid1]

md0 : active raid1 sda1[0] sdb1[1]
      192640 blocks [2/2] [UU]

md1 : active raid1 sda5[0] sdb5[1]
      979840 blocks [2/2] [UU]

md2 : active raid1 sda6[2] sdb6[1]
      159661888 blocks [2/2] [UU]

unused devices: 

Regenerate initrd

Yes, this needs to happen again after the raid is complete!

#mkinitrd -o /boot/initrd.img-2.6.8-1-k7-smp-md 2.6.8-1-k7-smp

This is still a needed step! If initrd.img is generated with a degraded array you will end up with a degraded array every time you reboot! This includes when you install a new kernel-image pkg which runs a script that produces a initrd.img! You have been warned!

Regenerate /etc/mdadm/mdadm.conf

edit /etc/mdadm/mdadm.conf

Delete all but the top line

DEVICE /dev/sda* /dev/sdb*

Then run:

mdadm --detail --scan >> /etc/mdadm/mdadm.conf

Your final file should look like:

DEVICE /dev/sda* /dev/sdb*
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=4d58ade4:dd80faa9:19f447f8:23d355e3
   devices=/dev/sda1,/dev/sdb1
ARRAY /dev/md1 level=raid1 num-devices=2 UUID=3f1bdce2:c55460b0:9262fd47:3c94b6ab
   devices=/dev/sda5,/dev/sdb5
ARRAY /dev/md2 level=raid1 num-devices=2 UUID=7dfd7fcb:d65245d6:f9da98db:f670d7b6
   devices=/dev/sdb6,/dev/sda6

Note - you need the top DEVICE line and the lower devices lines 

Configure grub to boot from both drives

Install the MBR on the second disk

#grub --device-map=/boot/grub/device.map

>> root (hd0,0)
>> setup (hd0)
>> root (hd1,0)
>> setup (hd1)
>> quit 

Have Grub point to your MD root device. Note that things after the '#" symbol make a difference here (note to grub developers: this confuses people why not use a different delimiter?)

Edit /boot/grub/menu.lst 

## default kernel options for automagic boot options
## If you want special options for specifiv kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
# kopt=root=/dev/sda6 ro

TO

## default kernel options for automagic boot options
## If you want special options for specifiv kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
# kopt=root=/dev/md2 ro

Setup the monitoring daemon

Just run:

dpkg-reconfigure mdadm

Test Test and Test

Test boot from both drives

Kill a drive and see if you get a email about the event.

Write up a step by step procedure to restore from a drive outage. (send a copy this way for this page!)

You should be all finished!

Please send notes of any typos/corrections to the email address below.

Special thanks to Onni Koskinen of Finland, whose gentle yet expert emails removed several glaring errors on this page and resulted in a vastly improved document.

Q & As

Re: section on configuring GRUB: will GRUB automatically boot from the
good drive in the event of a disk failure?

Yes, IF you install Grub on both drives and your BIOS will roll over to the first bootable drive.

How do you see what is in a initrd file?

mount -o loop /tmp/myinitrd /mnt/myinitrd

Notes from others:

I would like to add that this in fact maps the device names /dev/mdx to
the physical drives. In your setup, this does not matter because you
have md0, md1, md2, ... However when you produce a setup of for example:
/dev/md0 for /
/dev/md4 for /var
/dev/md5 for /mnt

And you do not create the mdadm.conf file, your device names will differ
into:
/dev/md0 for /
/dev/md1 for /var
/dev/md2 for /mnt

More info can be found in the file /etc/init.d/mdadm-raid that is run at
bootup before the mounting starts.
In their, you will run:
mdadm -A -s -a.

However if the /etc/mdadm/mdadm.conf file is empty, it will run
mdrun
which will assign numbers md0, 1, 2, and so on.


A second note when using udev on 2.6 kernels (as far as I know, not
tested on 2.4), you need to point you DEVICE line
in /etc/mdadm/mdadm.conf to the "static" entries as otherwise the system
will not find it at boot time.

So for example in case of UDEV:
your /etc/mdadm/mdadm.conf should look like:

DEVICE /dev/.static/dev/sda* /dev/.static/dev/sdb*
ARRAY /dev/md0 level=raid1 num-devices=2 spares=1
UUID=5c88a427:c5655de8:b97d2fa2:f5b1627e
   devices=/dev/.static/dev/sda1,/dev/.static/dev/sdb1