Use the following method only if you want to have a dual-boot system with Debian and the other operating system on the same Serial ATA RAID:
Boot from a Debian installation media.
Move the cursor to the Install boot menu entry (do not hit Enter yet):
Press Tab to edit the kernel boot line.
Add dmraid=true to the end of the line.
Press Enter.
In the boot menu, go to Advanced Options, and move the cursor to "Rescue system" (do not hit Enter yet):
Press Tab to edit the kernel boot line.
Press Enter.
(Optional) Type bash into the prompt, for easier command line editing and command history.
Modify /etc/default/grub (e.g. nano /etc/default/grub) and uncomment GRUB_DISABLE_LINUX_UUID=true (699437). Save the file and exit the editor.
Type update-grub and press enter. This is very important, because otherwise the GRUB boot menu later wont be able to display your freshly installed kernel!
Type grub-install /dev/mapper/ and press tab and tab again, you will get the names of the fake raid partitions.
Complete grub-install /dev/mapper/ with the name of your whole fake disk.
For example grub-install /dev/mapper/isw-jggdha7s-SYS (Note that there is no number at the end of the name). You may have something like /dev/mapper/isw-jggdha7s-SYS and /dev/mapper/isw-jggdha7s-SYS1, or /dev/mapper/isw-jggdha7s-Volume and /dev/mapper/isw-jggdha7s-Volume1. Choose the one without the partition number and press enter.
Type exit (twice if you did step 11). Now you should be back in the rescue system menu. Choose the Reboot system option. Now boot off your fake RAID and see GRUB starting your new Debian installation.