USB devices mess up Linux device enumeration
The Dell Virtual Flash and Virtual Floppy always become /dev/sda, /dev/sdb, respectivally. The local PERC disk then becomes /dev/sdc and our boot LUN on the SAN ends up at /dev/sdd. Turning the Dell devices on or off on BIOS then shuffles your devices around and suddenly your boot LUN will be sdb or sdc. No real danger, but /etc/fstab will no longer be valid and booting the system either gives you the maintenance shell or X1 will fail and you get a text login prompt (i.e. runlevel 3).
One, you can use device labelling or udev naming to have the kernel trace the partitions it needs. However, a quick solutions is - during production - to turn off USB devices by appending a parameter to the kernel. Adding "nousbstorage" to your kernel line (in grub or on the console) solves the issue too.