Like this ?
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a device; this may
# be used with UUID= as a more robust way to name devices that works even if
# disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
UUID=a4f552a4-21c8-4da3-932a-f72d289bfde6 / ext4 defaults,noatime 0 1
tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0
UUID=46994f1c-f1a8-4687-a5af-6ebe09e30798 /mnt/sda1 nofail ext4 defaults,noatime 0 2
UUID=77d462a0-1576-4eed-b18d-bbafea04c24a /mnt/sda2 ext4 defaults,noatime 0 2
UUID=9c09fd9d-f36b-42b6-9ca5-bfeb6219d0e5 /mnt/sda5 ext4 defaults,noatime 0 2
UUID=23c7fa5a-28fb-49e3-854a-638bfec7844c /mnt/sda6 ext4 defaults,noatime 0 2
The system won’t boot up if the process went to booting from /sda1. I need to perform Kresimir’s tip magic SysReq key many times in order to get correct boot drive, though chances of happening from this method is very low.
I am only left with force poweroff in order to get the correct boot drive.