I did a fresh installation of one of my server, including upgrade of all disks.
When rebooting in a fresh Debian installation I got stuck with the message "Scanning for devices. Please wait, this may take several minutes".
After 5 hours of trial and error, reading manuals and posts I found the solution.
In the PERC Raid Controller I had to create two new virtual disks and the boot order of the virtual disks which you can assign in the RAID Controller configuration was set to the wrong virtual disk...