OS doesn't see the partitions after reboot

[dt]

I have tried to install GuixSD on my non-UEFI PC from USB and I have
encountered multiple problems.

1) The USB is /dev/sda while HDD is /dev/sdb during the installation,
but after reboot HDD becomes /dev/sda.
How do I set the device for the bootloader and swap partition without
using device tree name (/dev/sdX)?

2) I have set the labels on HDD partitions this way:
/dev/sdb1 (ext4) - boot
/dev/sdb2 (ext4) - root
/dev/sdb3 (swap) - swap
/dev/sdb4 (ext4) - home

The config file for my system is attached.

After invoking `guix system init /mnt/etc/config.scm /mnt` and rebooting
the OS fails to mount the partitions because it doesn't detect them.

;; This is an operating system configuration template
;; for a "desktop" setup with GNOME and Xfce.

(use-modules (gnu) (gnu system nss))
(use-service-modules desktop)
(use-package-modules certs)

(operating-system
  (host-name "oldpc")
  (timezone "Europe/Minsk")
  (locale "ru_RU.UTF-8")

  ;; Assuming /dev/sdX is the target hard disk, and "my-root"
  ;; is the label of the target root file system.
  (bootloader (grub-configuration (device "/dev/sdb")))
  (file-systems (cons* (file-system
                        (mount-point "/")
                        (type "ext4")
                        (title 'label)
                        (device "root"))
			(file-system
                        (mount-point "/boot")
                        (type "ext4")
                        (title 'label)
                        (device "boot"))
			(file-system
                        (mount-point "/home")
                        (type "ext4")
                        (title 'label)
                        (device "home"))
                      %base-file-systems))
  (users (cons* (user-account
                (name "dt")
                (group "users")
                (supplementary-groups '("wheel" "netdev"
                                        "audio" "video"))
                (home-directory "/home/dt"))
		(user-account
                (name "guest")
                (group "users")
                (supplementary-groups '("wheel" "netdev"
                                        "audio" "video"))
                (home-directory "/home/guest"))
               %base-user-accounts))

  ;; This is where we specify system-wide packages.
  (packages (cons* nss-certs         ;for HTTPS access
                   %base-packages))

  ;; Add GNOME and/or Xfce---we can choose at the log-in
  ;; screen with F1.  Use the "desktop" services, which
  ;; include the X11 log-in service, networking with Wicd,
  ;; and more.
  (services (cons (xfce-desktop-service)
                   %desktop-services))

  ;; Allow resolution of '.local' host names with mDNS.
  (name-service-switch %mdns-host-lookup-nss))

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