While testing a SCSI controller with Ubuntu 16.04, I noticed some strange things concerning disk definition order...
Examples of different disk compositions and their 'sdx' definitions after booting:
1)
Sata HD -> sda
USB disk -> sdb
2)
SCSI HD -> sda
USB disk -> sdb
Sata HD -> sdc
3)
SCSI CD-ROM (no sdx definition given)
USB disk -> sda
Sata HD -> sdb
So, what is the logic in these results...? Why adding a SCSI disk (even when there is no sdx definition given to it) seems to reverse the defintion order of Sata and an USB disks? This is not just a curiosity because if the sdx definition of your boot disk changes you get Kernel panics and have to change Bootargs...
( I do not dare even guess what might happen if also an additional Sata controller would be present! )