Table of Contents

Booting from iSCSI with Debian Lenny

Introduction

This howto is similar to how to get iSCSI working with Debian Etch. It is important to note the following differences from that howto:

Doing iSCSI the lenny way

Install open-iscsi 

aptitude install open-iscsi

Touch the indicatorfile, which is queried to determine whether the iscsi tools and scripts are to be copied into the new initrd 

touch /etc/iscsi/iscsi.initramfs

Rebuild your initrd. 

aptitude install initramfs-tools
update-initramfs -u

Configure the parameters to your kernel with the following goals in mind:

Example: 

title           Debian Lenny iSCSI
   kernel       /vmlinuz-2.6.28-11-generic ISCSI_INITIATOR=iqn.2009-04.mynet:general iSCSI_TARGET_NAME=iqn.2009-04.mynet.node1:general.vol1 iSCSI_TARGET_IP=192.168.1.1 ISCSI_TARGET_PORT=3260 root=UUID=021ebcfc-188a-41ba-9864-ee18cbf7af9f ro
   initrd       /initrd.img-2.6.28-11-generic

Try to boot!

Lenny doesnt fetch from iBFT

Now if Open-iSCSI is in the repositories then why did I bother to write this howto? Good question! The answer is simply that you don't get the same result with the iSCSI + Etch howto as you get when instlling open-iscsi from the lenny repositories. While the “etch solution” fetches iscsi parameters from the iBFT, the “built-in lenny solution” fetches the parameters from configuration file(s) under /etc/ in the initramfs image itself and/or settings passed as kernel parameters from the bootloader.

While this simple distinction might seem innocent enough, it really isn't. In many cases it is impracticalt to create a new initrd or root image to change the iscsi parameters. Luckily, for most people there is a more elegant way to get the parameters. The latest lenny kernel (as of 4. November 2009) has an iBFT function compiled in that makes fetching the iSCSI parameters from iBFT really easy. From your initrd script, simply traverse the directory /sys/firmware/ibft The files in there contain all the ibft information you could ever want.

FIXME I didn't follow this route, but if you do, please put the initramfs script you created here. You can get access to this wiki by asking in the #etherboot IRC channel at irc.freenode.org. Se below for the route I took, and consequently the script i made instead

UPDATE I found a patch that probably solves this! This patch might help: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=514924#4

Extras: XEN + iSCSI + Lenny + iBFT

I decided to share my experience with iSCSI + Xen on Debian Lenny because that is a very important part of my setup. If you don't know or don't care about Xen you can simply skip this section. In short, I want to configure all my webserver farm nodes to boot xen dom0 kernels over iSCSI for my little webhost company. The problem arises since the xen kernels prior to 2.6.32 does not populate /sys/firmware/ibft directory.

Solutions to XEN + iSCSI + Lenny + iBFT

There are 3 solutions to the problem of aquiering iSCSI data from the iBFT with a lenny XEN kernel in initrd:

/etc/initramfs-tools/hooks/iscsi_tcp

#!/bin/sh
set  -e
PREREQ=""
prereqs()
{
        echo "$PREREQ"
}
case $1 in
prereqs)
        prereqs
        exit 0
        ;;
esac
. /usr/share/initramfs-tools/hook-functions
# NOTE THIS WILL BE INCLUDED BY DEFAULT, SO ITS DISABLED HERE: [ -x /usr/sbin/iscsistart ] && copy_exec /usr/sbin/iscsistart /sbin
[ -x /usr/sbin/fwparam_ibft ] && copy_exec /usr/sbin/fwparam_ibft /sbin
[ -x /sbin/ip ] && copy_exec /sbin/ip /sbin
manual_add_modules iscsi_tcp
manual_add_modules ib_iser

/etc/initramfs-tools/scripts/local-top/iscsi_tcp

This script will run at the correct time during boot to bring up iSCSI. It has been verified to work in a XEN-Dom0 node. 

#!/bin/sh
set -e
PREREQ="udev"
prereqs()
{
        echo "$PREREQ"
}
case $1 in
prereqs)
        prereqs
        exit 0
        ;;
esac
 
echo ""
echo "Custom iSCSI Boot script for Debian Lenny starting..."
echo ""
 
modprobe -q iscsi_tcp
modprobe -q ib_iser
 
echo "Evaluating IBFT parameters"
for i in $(fwparam_ibft);
do
	#Strip of namespace
	V=$(echo $i | sed 's|network\([0-9]*\):|iSCSI_INITIATOR_\1_|' | sed 's|target\([0-9]*\):|iSCSI_TARGET_\1_|' | sed 's|iscsi-initiator\([0-9]*\):|iSCSI_INITIATOR_\1_|')
	echo "   Exporting $V"
	export $V;
done
 
echo "Bringing up the interface used to boot"
for i in $(ls /sys/class/net); do
       IFADDR=$(cat /sys/class/net/$i/address)
       if [ $IFADDR = $iSCSI_INITIATOR_0_HWADDR ]; then
               echo "   Using $i with MAC $IFADDR"
               export iSCSI_INITIATOR_0_IF=$i
       fi
done
 
echo "   Bringing up $iSCSI_INITIATOR_0_IF for iSCSI..."
ip link set $iSCSI_INITIATOR_0_IF up
 
echo "   Setting up networking on $iSCSI_INITIATOR_0_IF..."
ip addr add $iSCSI_INITIATOR_0_IPADDR/$iSCSI_INITIATOR_0_MASK brd + dev $iSCSI_INITIATOR_0_IF
ip route add default via $iSCSI_INITIATOR_0_GATEWAY
 
echo "Connecting to iSCSI target $iSCSI_TARGET_0_NAME on $iSCSI_TARGET_0_IPADDR..."
iscsistart -i $iSCSI_INITIATOR_0_NAME -t $iSCSI_TARGET_0_NAME -g 1 -a $iSCSI_TARGET_0_IPADDR
sleep 5

Important: remember to chmod +x both these scripts so that the are executable before updating your initrd

Conclusion

Configuring boot over iSCSI work in Debian Lenny can potentially be much easier than it was in Etch because of the built-in support for iSCSI boot made by Debian devs in Lenny. If you only have a few servers that you need to boot over iSCSI then using this metod is simple to set up and probably works great.

However if you have a setup with many computers (cluster) or need a more elegant way to manage your boot parameters for another reason then you will need to modify the default behaviour in Lenny, and this requires about half the amount of fiddeling required with Debian Etch.

However if you decide to boot XEN nodes like I showed in this example you need to fiddle just as much if not more than the Etch howto described :)