Network Boot - iSCSI

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20px   installation Network Boot - iSCSI

If you have any questions/corrections/contributions about this how-to, you're welcome on this OpenELEC forum topic

Introduction


Goals

  • Having a diskless (noiseless) HTPC no drive, so less noise (even SSD can make the device louder, because it will make the whole device warmer, and the fans – if you have fans – will make more noise).
  • On a Gigabit Ethernet network, iSCSI should be faster than any USB device.
  • To host everything on your lovely network storage device (for your media, I do not recommend to store them on an iSCSI target, NFS or CIFS shares are far better options in order to share them between several clients).

What Do You Need?

  • an iSCSI target it could be an end-user NAS(*) device (Synology, Qnap, Drobo... offers iSCSI on every devices they sell, even the end-user ones, Netgear offers iSCSI on enterprise class models), a home-made server using FreeNAS, OpenFiler, or any GNU/Linux distribution.
  • A little knowledge on how to configure your iSCSI target (creating LUNs, targets, etc.), as it will not be covered in this HowTo.
  • A DHCP/TFTP server or an SD card (or an USB device), more on this later.

FAQ


Do I really need to do that?

Shortcut:

Of course not! But you could, so you should, you know that!


Why not using a traditionnal PXE + NFS boot?

Shortcut:

You can do that, yes, the goals are exactly the same. The difference is that NFS is file-oriented, iSCSI is block-oriented. Using iSCSI, you will have access to a standard block device (/dev/sdX), as if it was a local disk, which you could find easier (or not) to use than NFS. ISCSI can also you file extents, which are basically just a disk image. ISCSI should be a little faster than NFS, cause there is far less overhead (no lock controls, no FS code on the target side.)


Why not using PXE + NBD boot?

Shortcut:

You can use that too, yes, the goals are still the same but NBD is not an adopted standard, it only exists on UNIX/Linux systems, and you probably won't find it on any commercial NAS/SAN devices...


Create the LUN/target on the iSCSI Target

This part is really dependent on your iSCSI target device, so it can't be covered in this HowTo

The LUN that you create will be used to store the OpenELEC System and Storage partitions, so size it as you want/need (4GB should be enough for starting, and there are chance that your iSCSI system allows you to resize your LUNs later – that's one good reason to use iSCSI, but you can give your system more or less space if you want).

Information That You Will Need

  • iSCSI target IP address (in my example 192.168.1.14)
  • The target Name (IQN) (in my example iqn.2000-01.com.synology:pandora.openelec)
  • If you have enabled the CHAP authentication username and password
  • If you have enabled the reverse CHAP authentication username_in and password_in


Installing OpenELEC on the iSCSI LUN

Accessing the LUN

So, your LUN is created, now you have to access it from your building system.

First you need to have iscsi support

aptitude install open-iscsi

Now you have to discover your iscsi portal

iscsiadm -m discovery -t st -p 192.168.1.14

That should list the available targets. In my example

192.168.1.14:3260,0 iqn.2000-01.com.synology:pandora.openelec

It should have created a config file in /etc/iscsi/nodes/iqn.2000-01.com.synology\:pandora.openelec/192.168.1.14\,3260\,0/default'

If you have configured CHAP authentication (and reverse CHAP), you should edit this file (adapt the path to your needs) and add

node.session.auth.authmethod = CHAP
node.session.auth.username = username
node.session.auth.password = password
node.session.auth.username_in = username_in
node.session.auth.password_in = password_in

And finally, login into the target

iscsiadm -m node -T iqn.2000-01.com.synology:pandora.openelec -p 192.168.1.14:3260 -l

If you have some errors like

Logging in to [iface: default, target: iqn.2000-01.com.synology:pandora.openelec, portal: 192.168.1.14,3260]
iscsiadm: Could not login to [iface: default, target: iqn.2000-01.com.synology:pandora.openelec, portal: 192.168.1.14,3260].
iscsiadm: initiator reported error (19 - encountered non-retryable iSCSI login failure)

Then, you should review your authentication configuration.

If everything went fine, you should see some logs on the terminal

Logging in to [iface: default, target: iqn.2000-01.com.synology:pandora.openelec, portal: 192.168.1.14,3260]>
Login to [iface: default, target: iqn.2000-01.com.synology:pandora.openelec, portal: 192.168.1.14,3260] successful.

Cool, now you have a new block device on your system.

dmesg | tail -n 8
[ 9648.232779] scsi4 : iSCSI Initiator over TCP/IP
[ 9649.246417] scsi 4:0:0:0: Direct-Access SYNOLOGY iSCSI Storage    3.1  PQ: 0 ANSI: 5
[ 9649.247062] sd 4:0:0:0: [sdc] 16777216 512-byte logical blocks: (8.58 GB/8.00 GiB)
[ 9649.248907] sd 4:0:0:0: [sdc] Write Protect is off
[ 9649.248915] sd 4:0:0:0: [sdc] Mode Sense: 3b 00 00 00
[ 9649.249371] sd 4:0:0:0: [sdc] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[ 9649.251819] sdc: sdc1 sdc2
[ 9649.253767] sd 4:0:0:0: [sdc] Attached SCSI disk

So for me it's /dev/sdc (there are already partitions on it, with a brand new LUN, that should of course not be the case). Remember what device it is for the next step (I will use /dev/sdX to refer to it, so people who does copy/paste will not destroy any existing data in the next steps).

Installing OpenELEC

Partitioning

First you have to create a partition table on your device.

You can use your preferred tool for that (fdisk, cfdisk, parted, …).

My favourite tool is cfdisk

cfdisk /dev/sdX
  • Create two partitions:
    • a 256MB (or more) one, that will hold the OpenELEC KERNEL and SYSTEM. Partition type should be Linux (83, which is the default). Make it bootable.
    • all the remaining space will be used as storage. Partition type should be Linux (83, which is the default)

Check that the partition table is fine

fdisk -l /dev/sdX
Disk /dev/sdX: 8589 MB, 8589934592 bytes
133 heads, 62 sectors/track, 2034 cylinders, total 16777216 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000eece8
 
  Device Boot      Start         End      Blocks   Id  System
/dev/sdX1   *         62      503005      251472   83  Linux
/dev/sdX2          503006    16777215     8137105   83  Linux

Formatting

Now you have to create the two filesystems, System and Storage (the labels are important to have OpenELEC booting fine, if you want/need to change them, you'll have to adapt the extlinux.conf file later)

mkfs.ext4 -L System /dev/sdX1
mkfs.ext4 -L Storage /dev/sdX2

Installing Openelec

Mount the System partition on your system

mkdir -p /mnt/openelec/system
mount LABEL=System /mnt/openelec/system

Copy the OpenELEC KERNEL and SYSTEM files in it :

cp /path/to/SYSTEM /mnt/openelec/system
cp /path/to/KERNEL /mnt/openelec/system

Installing the Extlinux Bootloader

First, create the extlinux.conf file

nano /mnt/openelec/system/extlinux.conf
 DEFAULT linux
 PROMPT 0
 
 LABEL linux
   KERNEL /KERNEL
   APPEND ip=dhcp boot=ISCSI='''ISCSI_OPTIONS''',LABEL=System disk=LABEL=Storage quiet

The ISCSI_OPTIONS will depend on how you will boot. You can edit it later.

Basically, there will be two options :

  • You will use an iBFT capable boot rom (IPXE), ISCSI_OPTIONS will be:
auto
  • You will not use an iBFT capable boot rom, ISCSI_OPTIONS will be something like (all on one line) :
iscsi_initiator=iqn.2010-04.org.whatever:mybox,iscsi_target_name=iqn.2000-01.com.synology,iscsi_target_ip=192.168.1.14,
iscsi_target_port=3260,iscsi_target_group=pandora.openelec iscsi_username=username,iscsi_password=password,
iscsi_in_username=username_in,iscsi_in_password=password_in

If you are a sane person, you probably already know that you will use an iBFT capable ROM like IPXE


Now install extlinux on the device

extlinux --install /mnt/openelec/system

Now unmount the device

umount /mnt/openelec/system

Now write the mbr (or gptmbr)

dd if=/usr/share/syslinux/mbr.bin of=/dev/sdx bs=440 count=1

And log out from the target

iscsiadm -m node -T iqn.2000-01.com.synology:pandora.openelec -p 192.168.1.14:3260 -u


Configuring the iSCSI Boot

Ok, so now you have your LUN and OpenELEC is installed on it, but how will you make your HTPC boot from it.

There is several answers to that question.

If you have the chance to have an HTPC which have an iSCSI compatible network adapter (most intel network adapters) it will be really easy just go into your network card BIOS/ROM, and configure the iSCSI target, and tell it to boot from it. You should be done!

You probably don't have such a network adapter (it's more an entreprise-class feature), but no problem, IPXE (http://ipxe.org) is there for you!

IPXE is an OpenSource Boot Firmware, it's a maintained fork of Etherboot/GPXE. It does PXE, is capable to access files from TFTP, FTP, HTTP servers, and more important it is also capable to boot from iSCSI (it also supports san boot on AoE and FCoE) !

TFTP Serving the IPXE Rom

Installing a DHCP and/or a TFTP server is out of the scope of this howto. You'll find good tutorials about that on the Net.

There are some good docs on the IPXE homepage about that

http://ipxe.org/howto/dhcpd

http://ipxe.org/howto/msdhcp

If you don't already have a DHCP server nor a TFTP server, I recommend you to look at dnsmasq, which is a lightweight DHCP/TFTP server

So basically, you just have to make the ipxe ROM available on your TFTP server, and configure the DHCP server to make your box boot on it (next-server...). Then, configure a DHCP chainloader (http://ipxe.org/howto/chainloading) to boot a script like

echo Ready for iscsi boot !
set username username
set password password
set reverse-username username_in
set reverse-password password_in
:retry_sanboot
sanboot iscsi:192.168.1.14::::iqn.2000-01.com.synology:pandora.openelec || goto retry_sanboot

Of course you will have to adapt it to your needs (ip address, target name, usernames and passwords).

Install the ROM on a Removable Device

You don't want to (or you can't) install and configure a DHCP server and a TFTP server.

And you have that old SD card of 128MB that you earned with your first digital camera years ago, that is of no use now... great! It's a perfect candidate for becoming a booting ROM device! (of course, if your HTPC doesn't allow you to boot from SD card, you'll need to find something else, like an old USB key (the smaller, the better).

Create a new text file, that will be your ipxe embeded boot script

#!ipxe
:retry_dhcp
dhcp || goto retry_dhcp
echo Ready for iscsi boot !
set username username
set password password
set reverse-username username_in
set reverse-password password_in
:retry_sanboot
sanboot iscsi:192.168.1.14::::iqn.2000-01.com.synology:pandora.openelec || goto retry_sanboot

Once again, adapt the values to your needs!

Building the ROM

rom-o-matic

You can use a service like rom-o-matic to automatically generate the IPXE rom for you

Select either (depending on your method)

  • USB Keychain disk image (.usb)
  • UNDI only (.kpxe)

Paste your script into the text box and select Proceed

Build from Source

git clone git://git.ipxe.org/ipxe.git
cd ipxe/src
make bin/ipxe.usb EMBED=~/my_script.ipxe

or

make bin/undionly.kpxe EMBED=~/my_script.ipxe

Writing the boot ROM

Just put it on your SD card/USB device (plug it on your building system, look at dmesg to find on which /dev/sdX it is available).

dd if=ipxe.usb of=/dev/sdX


Just put the SD card/USB key in your HTPC box, configure it to boot from it, and enjoy!