Setting up Debian on a Serial ATA RAID device

This page explains how to use Debian Installer to set up Debian on a Serial ATA (SATA) RAID disk (using dmraid).Note that support for SATA RAID is experimental and is only available in the Lenny version of the installer.SATA RAID support has been significantly improved after the Lenny Beta 2 release, especially with regard to partitioning. Users are therefore strongly advised to use either daily built images or Lenny Release Candidate (RC) images.SATA RAID is only supported for the architectures i386 and amd64.There have not yet been any tests installing Debian alongside an existing Windows installation. We expect that that is possible, but there is a risk that the Windows partition will become corrupted. It is strongly recommended that you make a backup of any data on your system that you do not wish to lose before using this option.

SATA RAID or Software RAID

The RAID support offered by most Serial ATA disk controllers is not hardware RAID. Instead it can best be classified as “software RAID provided by the BIOS of the controller”.Various terms are used to refer to this type of RAID support: SATA RAID, BIOS RAID, fake RAID, software RAID. We have decided to use the term SATA RAID. We prefer to reserve the term “software RAID” to refer to the RAID support in the Linux kernel.The general consensus is that using Linux software RAID is to be preferred over using this relatively cheap, and because of that possibly less reliable, software RAID offered by SATA disk controllers.However, if your system already has another operating system installed on a SATA RAID disk and you want to install Debian alongside that, using dmraid is basically your only option.In all other cases we strongly suggest that you use Linux software RAID (using the mdadm package), which is also much better supported by the installer.Of course, if your system has a SATA-based RAID controller that does offer real hardware RAID, you should just completely ignore the information on this page.

Booting the installer

Because the support for SATA RAID is still experimental, you will need to boot the installer with a special boot parameter ‘dmraid=true‘.This parameter can be added by first pressing the <TAB> key at the desired option in syslinux menu and then entering the option.

Hardware detection

When the boot parameter is passed, the SATA RAID disk should be automatically detected and if it is detected, some additional installer components will be loaded.If it’s not detected, please file an installation report! The syslog can be checked for possible causes of a failure to detect the hardware.

Partitioning

Starting with the Lenny RC1 release partitioning of SATA RAID disks is completely supported. The RAID disk can be partitioned just like a normal hard disk, including the use of “guided partitioning”, LVM and encryption.See the installation guide for further details.

Boot loader installation

SATA RAID devices are currently not really supported by either grub or lilo, basically because its not possible to probe the BIOS for the device. But it is possible to install grub using a semi-manual method. This method has been implemented in grub-installer. Only grub (“grub legacy”) is supported, not grub-pc (“grub2”).Using lilo is currently not supported, but it may be possible to set up lilo manually if you prefer.The installer will automatically detect if /boot is on a dmraid device and will then install grub in the master boot record (MBR) of that device. No other options will be offered.
As the current installation procedure assumes that the SATA RAID device is (hd0), the SATA RAID disk should be listed as the first hard disk in the boot order in your BIOS configuration.In case of problems, please check the log file /var/log/grub-dmraid.log.The os-prober component should detect the presence of other operating systems such as Microsoft Windows on the SATA RAID device, but the bootloader may not be correctly configured to boot those. It should be possible to make other operating systems boot correctly with minor changes in the GRUB configuration.

Installing GRUB manually

The installer basically runs ‘grub’ and executes some commands in the GRUB command interface. This example gives an impression of the commands executed by the installer (values between ‘<>’ should be changed according to your situation):  

# grub  --device-map=/dev/null
grub> device (hd0,<1>) /dev/mapper/<isw_dhiiedgihc_Volume02>
grub> device (hd0) /dev/mapper/<isw_dhiiedgihc_Volume0>
grub> root (hd0,<1>)
grub> setup (hd0)
grub> quit

You can of course perform this procedure manually if you want to change your GRUB installation, or if you need a different setup than the installer currently offers. See Gerte’s page for details.

Remember that the GRUB partition number is one less than the actual partition number as GRUB numbers partitions starting at zero.