External SSDs as Gentoo boot drive (Samsung Portable SSD T3/T5/T7)

samsung-portable-ssd-gentoo

1. Emerge gentoo-sources and upgrade your kernel (skip if you don't wanna upgrade your kernel)
2. eselect kernel list and then eselect kernel set <number> where <number> is the kernel you're using
3. cd to /usr/src/linux (/mnt/gentoo/usr/src/linux if not chrooted) and make menuconfig
4. Device Drivers -> USB support -> USB Mass Storage support <M>
5. Device Drivers -> USB support -> USB Attached SCSI <M>
6. General Setup -> Initial RAM filesystem and RAM disk (initramfs/initrd) support [*]
7. General Setup -> Support initial ramdisk/ramfs compressed using LZ4 (or something else if you're not using LZ4)
8. Save and exit
9. Mount your /boot partition
10. make -jX && make modules_prepare && make modules_install && make install
11. emerge genkernel
12. genkernel --kernel-config=/usr/src/linux/.config initramfs
13. mkdir -p /etc/modules-load.d
14. vim /etc/modules-load.d/network.conf and add:
uas
usb-storage
to the file and :wq
15. grub-mkconfig -o /boot/grub/grub.cfg (if necessary)
16. Reboot and enjoy.