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 4B with an id: 0dc0a15d and a name: rpi4-1.

  • 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 Raspbian Buster lite image.

The downloaded image has a rootfs which is about 1.5GB large. For MicroMEC we need a rootfs that is 4GB at least. We will need to copy the rootfs from the buster image to a large enough image file.

  1. Extract the downloaded Raspbian Buster lite image

     $ cd /tmp

 $ mkdir raspbian_buster

 $ unzip 2020-02-13-raspbian-buster-lite.zip
 Archive:  2020-02-13-raspbian-buster-lite.zip
   inflating: 2020-02-13-raspbian-buster-lite.img

  2. Setup a virtual loopback device using the extracted image

     $ sudo losetup -fP 2020-02-13-raspbian-buster-lite.img
 
 $ lsblk
 NAME               MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
 loop0                7:0    0   1.7G  0 loop  
 ├─loop0p1          259:0    0   256M  0 part  
 └─loop0p2          259:1    0   1.5G  0 part 
 ...

  3. Mount the rootfs partition from the extracted image. The rootfs is available via /dev/loop0p2 in our case.

     $ mkdir raspbian_rootfs
 
 $ sudo mount /dev/loop0p2 raspbian_rootfs

  4. Create a virtual loop back device that will hold the resized rootfs

     $ cd /tmp

 $ dd if=/dev/zero of=0dc0a15d-raspbian-rootfs.img bs=400M count=10

 $ sudo mkfs.ext4 0dc0a15d-raspbian-rootfs.img

 $ sudo losetup -fP 0dc0a15d-raspbian-rootfs.img

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

     $ losetup -a
 /dev/loop1: []: (/tmp/0dc0a15d-raspbian-rootfs.img)
 /dev/loop0: []: (/tmp/2020-02-13-raspbian-buster-lite.img)

  6. Mount the new virtual block device

     $ mkdir 0dc0a15d-rootfs-mount
 
 $ sudo mount -o loop /dev/loop1 0dc0a15d-rootfs-mount

  7. Copy the content of the Rasbian Buster rootfs to the mounted block device

     $ sudo cp -R /tmp/raspbian_rootfs/* 0dc0a15d-rootfs-mount/

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

     $ sudo umount 0dc0a15d-rootfs-mount

 $ sudo losetup -D

 $ sudo mkdir /srv/iscsi

 $ sudo mv 0dc0a15d-raspbian-rootfs.img /srv/iscsi

  9. Prepare the iscsi target and publish it

     $ sudo tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.org.micromec:rpi4-1-raspbian-rootfs

 $ sudo tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b /srv/iscsi/0dc0a15d-raspbian-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.

  10. 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:rpi4-1-raspbian-rootfs

    Login to the iscsi target

     $ sudo iscsiadm -m node --targetname iqn.org.micromec:rpi4-1-raspbian-rootfs  -p localhost -l
 Logging in to [iface: default, target: iqn.org.micromec:rpi4-1-raspbian-rootfs, portal: 127.0.0.1,3260] (multiple)
 Login to [iface: default, target: iqn.org.micromec:rpi4-1-raspbian-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:rpi4-1-raspbian-rootfs

    Login to the iscsi target

     $ sudo iscsiadm -m node --targetname iqn.org.micromec:rpi4-1-raspbian-rootfs -p bootserv -l
 Logging in to [iface: default, target: iqn.org.micromec:rpi4-1-raspbian-rootfs, portal: 192.168.4.1,3260]
 Login to [iface: default, target: iqn.org.micromec:rpi4-1-raspbian-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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