CH3SNAS when using 1 disk, no matter which slot you are using: it will always be Volume_1 (standard mode or normal mode). Under the hood the Volume_1 is a a symbolic link to sda or sdb. If inserted left Volume_1 is a symbolic link to sdb if inserted right: the disk is sda
So at the bottom: the sda and sdb will make a reverse change, so the user won’t notice it has changed
So if you want to have sda equal to Volume_1 in all circumstances: start using the HDD in the right HDD tray.