RPi 4B iscsi how-to

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