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Inspiration from hiroom2.com. Kudos!

Foreword

These steps are meant to be completed on a Linux computer that serves as a netboot server of the MicroMEC cluster. The steps can of course be adopted for other use cases.

  • Our netboot server (ie. iscsi target server) is called bootserv.

  • The netboot server is available on the LAN and can be pinged using the name bootserv.

  • We refer to the RPi 3B+ with an id: 07f32691 and a name: rpi3-1.

  • We use sudo and start the preparations in /tmp on the netboot server.

Security Note

The setup is meant for a private lab. Security considerations for exposing the rootfs via the LAN are not discussed in this how-to as of now.

Prerequisites

  • A computer running Debian Linux. Any Linux flavor can be used, but our instructions refer to Debian.

  • 15GB free space on the hard drive.

  • Installed packages: tgt, open-iscsi.

  • Fast LAN (preferably Gigabit Ethernet).

Steps

  1. Download a ready made rootfs from the Open Build Service.

    We will use openSUSE Tumbleweed on our RPi 3B+:

  2. Extract the downloaded rootfs

     $ cd /tmp

 $ mkdir openSUSE_Tumbleweed

 $ xz -d /tmp/openSUSE-Tumbleweed-ARM-JeOS.aarch64-rootfs.aarch64-2020.05.10-Snapshot20200512.tar.xz

 $ cd openSUSE_Tumbleweed

 $ tar xvf /tmp/openSUSE-Tumbleweed-ARM-JeOS.aarch64-rootfs.aarch64-2020.05.10-Snapshot20200512.tar.xz

  3. Create a virtual loop back device that will hold the rootfs:

     $ cd /tmp

 $ dd if=/dev/zero of=07f32691-opensuse-rootfs.img bs=400M count=10

 $ sudo mkfs.ext4 07f32691-opensuse-rootfs.img

 $ sudo losetup -fP 07f32691-opensuse-rootfs.img

  4. Check which loopback devices are allocated by the kernel:

     $ losetup -a
 /dev/loop0: []: (/tmp/07f32691-opensuse-rootfs.img)

  5. Mount the virtual block device

     $ mkdir 07f32691-rootfs-mount
 
 $ sudo mount -o loop /dev/loop0 07f32691-rootfs-mount

  6. Copy the content of an existing rootfs image to the mounted block device

     $ cp -R /tmp/downloaded_rootfs/*  07f32691-rootfs-mount/

  7. Unmount the file and move it to the place where it will be served.

     $ sudo umount 07f32691-rootfs-mount

 $ sudo losetup -D

 $ sudo mkdir /srv/iscsi

 $ sudo mv 07f32691-opensuse-rootfs.img /srv/iscsi

  8. Prepare the iscsi target and publish it

     $ sudo tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.org.micromec:rpi3-1-opensuse-rootfs

 $ sudo tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b /srv/iscsi/07f32691-opensuse-rootfs.img

 $ sudo tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL

    Note

    If your iscsi server has other targets then you will need to pick a different tid.

    At this point the rootfs is available on the local network.

  9. Save the configuration on the netboot server to remain persistent

     $ sudo tgt-admin --dump | sudo tee  /etc/tgt/conf.d/micromec-cluster.conf

Local Testing

  1. Check the iscsi target locally

    Discover the iscsi target

     $ sudo iscsiadm --mode discovery --op update --type sendtargets --portal localhost
 127.0.0.1:3260,1 iqn.org.micromec:rpi3-1-opensuse-rootfs

    Login to the iscsi target

     $ sudo iscsiadm -m node --targetname iqn.org.micromec:rpi3-1-opensuse-rootfs  -p localhost -l
 Logging in to [iface: default, target: iqn.org.micromec:rpi3-1-opensuse-rootfs, portal: 127.0.0.1,3260] (multiple)
 Login to [iface: default, target: iqn.org.micromec:rpi3-1-opensuse-rootfs, portal: 127.0.0.1,3260] successful.

    Check if a new partition appears in the list:

     $ cat /proc/partitions
 major minor  #blocks  name
 .....
    8       32    4096000 sdc

    Mount the partition to a mount point

     $ mkdir /tmp/test-rootfs

 $ sudo mount /dev/sdc /tmp/test-rootfs

 $ ls -alrt /tmp/test-rootfs

    Umount the partition

     $ sudo umount /tmp/test-rootfs

    Logout from all iscsi targets

     $ sudo iscsiadm -m node -U all

Remote Testing

  1. Check the iscsi target remotely

    Login to an other Linux computer which also has the open-iscsi tools installed.

    Discover the iscsi target

     $ sudo iscsiadm --mode discovery --op update --type sendtargets --portal bootserv
 192.168.4.1:3260,1 iqn.org.micromec:rpi3-1-opensuse-rootfs

    Login to the iscsi target

     $ sudo iscsiadm -m node --targetname iqn.org.micromec:rpi3-1-opensuse-rootfs -p bootserv -l
 Logging in to [iface: default, target: iqn.org.micromec:rpi3-1-opensuse-rootfs, portal: 192.168.4.1,3260]
 Login to [iface: default, target: iqn.org.micromec:rpi3-1-opensuse-rootfs, portal: 192.168.4.1,3260] successful.

    Check the available partitions

     $ cat /proc/partitions
 major minor  #blocks  name
 .....
    8       16    4096000 sdb

    Mount the partition to a mount point

     $ mkdir /tmp/test-rootfs

 $ sudo mount /dev/sdb /tmp/test-rootfs

 $ ls -alrt /tmp/test-rootfs

    Umount the partition

     $ sudo umount /tmp/test-rootfs

    Logout from all iscsi targets

     $ sudo iscsiadm -m node -U all
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