Not like it's a problem so far, but mostly my curiosity. I have 2 disks -- internal and external. The latter is connected via USB3 cable. My Ubuntu install is on the external drive. W10 is inside my laptop (it's a dual-boot system). So usually my internal drive is sda and my external one is sdb in Ubuntu (they're both SATA drives, of course). But today they switched their device names, so the internal became sdb and external became sda. After the reboot everything got back to normal. I personally haven't done anything in this regard. To me that's strange. Maybe someone could explain that to me, please.