Lenny (5.0) and later support having the root and /boot partition on RAID volume. Actually, you can have root on RAID1+LVM partition.
This page contains some screenshots to demonstrate it, and applies to Debian 5.0 through, at least, 8.0.
Root on software RAID+LVM
In this example, we use virtual machine (qemu or kvm)... we can play, and break them 
$ sudo apt-get install kvm $ qemu-img create -f qcow2 hda.qcow2 4G Formatting 'hda.qcow2', fmt=qcow2, size=4194304 kB $ qemu-img create -f qcow2 hdb.qcow2 4G Formatting 'hdb.qcow2', fmt=qcow2, size=4194304 kB $ kvm -hda hda.qcow2 -hdb hdb.qcow2 -cdrom debian-lenny-i386-netinst.iso -boot d
Of course, you need to download a cdrom image.
Root on RAID+LVM example
Those few screenshots show how to install root on lvm on raid :
Once you have reach DebianInstaller partitioning screen...
Choose manual partitioning, then on each disk, manually create a partition (same size on both disks).
Create partitions for RAID
Use as "Physical volume for Raid" :
Configure RAID
We have a raid partition on each disk:
Choose the type of multidisk device to be created:
We have two partition:
- (In this example, we have no spare partition).
Let's select the partitions to use:
That's it !
Configure LVM
Let's configure the Logical volume manager:
First create a volume group:
Here, I chose the name vg1 for the group:
We have only one raid device:
Let's create the logical volume (kind pf partitions):
Our Logical volume (LV) will use some disk space from vg1 (which belongs to md0):
I named my partition foobar_root:
In this example, we wont split the filesystem (we won't even bother to create a swap, which is a bad idea), so I use all the disk space. (which again isn't a good idea, since it's so easy ro resize a partition with LVM)
Finish:
Use the LVM volumes
Let's assign and format the volumes (partitions):
As usually...
Done!
Install the bootloader (GRUB)
In Jessie (8.0), and I believe Wheezy (7.0), the installer will install GRUB even on RAID installs. However, GRUB can not install to a RAID device (e.g., /dev/md0), but will nonetheless work fine.
When asked to install bootloader, install to first device:
attachment:After first boot, consider executing dpkg-reconfigure grub-pc (or dpkg-reconfigure grub-efi-amd64 on EFI systems), and install to all devices. This way, your system will still boot correctly even if you reorder your drives.
attachment:
Install the bootloader (lilo)
At the end of the installation...
In Lenny (5.0), DebianInstaller automatically switch to lilo when you have root on RAID:
Reboot Debian
Debian is booting:
Using D-I rescue, to reinstall lilo
Thanks to DebianInstaller's rescue mode, it's very easy to recover a problem :
Simply boot on the CD, and choose rescue mode, then after the usual DI prompt, you get :
Then:
Reinstall/ rescue/restore lilo :
See also
Recover a DegradedArray RAID array
http://lists.debian.org/debian-user/2008/10/msg01989.html