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====== Booting via iSCSI ======

This tutorial describes a simple three-step process for getting your first iSCSI-booting operating system up and running.  The three stages are:

  * [[#Preparing the operating system image]]
  * [[#Transferring the operating system image to an iSCSI target]]
  * [[#Booting the operating system from the iSCSI target]]

===== Preparing the operating system image =====

The first stage is to prepare the operating system image for iSCSI boot.  This generally involves installing an iSCSI initiator and adjusting a few configuration parameters.  Instructions are available for:

  * [[iscsibootprepfc5|Fedora Core 5]]

===== Transferring the operating system image to an iSCSI target =====

The second stage is to transfer the prepared operating system image from the iSCSI boot machine to a remote iSCSI target.

If you do not have an iSCSI NAS box, you probably want to set up the Linux software iSCSI target.  You can find prepackaged versions at http://sourceforge.net/project/showfiles.php?group_id=177003; you need to download and install the ''iscsitarget'' and ''dkms-iscsi_trgt'' RPMs.

There are several possible ways to perform the transfer:

  * Physically move the disk containing the prepared operating system image into the iSCSI  target.
  * Copy the disk image containing the prepared operating system image to a file on the iSCSI target using ''dd'' and ''netcat''.
  * Create an empty filesystem on the iSCSI target and copy the contents across using ''rsync -ax''.  Note that this method will require you to manually reinstall the bootloader (LILO or grub) after the transfer; if you don't know how to do this then don't use this method.

The easiest way for a first-time user is probably to physically transfer the disk to the iSCSI target and then add this disk to the export list.  If you are using the Linux software iSCSI target, then you can do this by editing ''/etc/ietd.conf'' and adding an entry such as

  Target iqn.2006-09.com.example.myhost:storage
    Lun 0 Path=/dev/hdb

(assuming that the hostname of the iSCSI target is ''myhost.example.com'' and the newly attached disk is ''/dev/hdb'').  The target name should follow the format of the example above.

===== Booting the operating system from the iSCSI target =====

The third stage is to configure the network card for iSCSI boot, and then to attempt booting.

You need a network card boot ROM that supports iSCSI boot.  If your NIC vendor does not already supply such a ROM, you can build your own using

  cvs -d:pserver:anonymous@etherboot.cvs.sourceforge.net:/cvsroot/etherboot login 
  cvs -z3 -d:pserver:anonymous@etherboot.cvs.sourceforge.net:/cvsroot/etherboot co -P gpxe
  cd gpxe/gpxe-0.5/src
  make bin/rtl8139.rom

which will give you a boot ROM image for a RealTek 8139-based network card.  Many other cards are available; if you can't find the one you need then ask on <etherboot-discuss@lists.sourceforge.net> for help.

For experimentation, you may prefer to build a "boot ROM on a floppy", which you can do by changing ''.rom'' to ''.dsk'', e.g.

  make bin/rtl8139.dsk

This will give you a bootable floppy disk containing the boot ROM code, which may make testing easier.  Once you have later verified that everything works, you can burn the code into the ROM.

You need to set up your DHCP server to request iSCSI boot.  Edit /etc/dhcpd.conf and change or add the line

  filename "iscsi:192.168.0.1:iqn.2006-09.com.example.myhost:storage";

where ''192.168.0.1'' is the IP address of your iSCSI target, and ''iqn.2006-09.com.example.myhost:storage'' is the target name.((Yes, we know that this usage of the filename field doesn't comply with RFC4173; this will be fixed.))

Now boot the iSCSI boot machine using the iSCSI boot ROM (or iSCSI boot floppy, if you are using a floppy disk for experimentation).  You should see the usual bootloader screen (LILO, grub or NTLDR, for example) appear, and the operating system will start as normal.

Congratulations!  You have successfully booted an operating system from a remote iSCSI disk.  If you encounter difficulties, please feel free to ask questions on the etherboot-discuss mailing list at <etherboot-discuss@lists.sourceforge.net>.  If you have an urgent question, [[consultancy|professional support]] is available on a consultancy basis.
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