Boot from small USB drive with iscsi root filesystem

Boot from small size USB drive only holding boot partitions, rest of filesystems are on iscsi drives. Tested in EFI boot in Fedora 34.

Requirement

• /boot partition can be 256M, can be very small, but better bigger

Filesystem                         Size  Used Avail Use% Mounted on
/dev/sdb2                          428M  190M  212M  48% /boot

• /boot/efi is an almost static very small filesystem, can be very small

Filesystem                         Size  Used Avail Use% Mounted on
/dev/sdb1                          512M   31M  482M   6% /boot/efi

grub configuration

Define iscsi login info

GRUB_CMDLINE_LINUX="netroot=iscsi:<user>:<password>@<ip>::3260::<iqn> rd.iscsi.initiator=<client iqn> rhgb quiet ...

Define network interface with static ip 192.168.1.2, gateway 192.168.1.254, nameserver 192.168.1.1, interface enp0s10.

ip=192.168.1.2::192.168.1.254:255.255.255.0::enp0s10:off nameserver=192.168.1.1

Define network with bridge interface br0 on network interface enp0s10

ip=192.168.1.2::192.168.1.254:255.255.255.0::br0:off nameserver=192.168.1.1 ifname=enp0s10:xx:xx:xx:xx:xx:xx bridge=br0:enp0s10"

Update grub using following command

grub2-mkconfig -o /boot/grub2/grub.cfg