hello george1421,
thank you for your support. its a “3ware” raid controller.
its possible to use FOG to clone these disk structures but you need to know ahead of time
yes, i did understand this later 
sorry for going to ask maybe some “dumb” questions now , but i am really a little bit nervous about this situation. its a very old system (win-xp, so over 15 years old) and it contains very important data. but i could create a backup - so thats the good news.
i am trying not to miss something, which could effort a lot more work.
a.) what if i do remove the wrong hdd and reattach it again?
e.g. i do remove the sdb, i start the computer, noticing this mistake, turning off the computer, reattaching sdb and removing sda.
do i have to worry about losing data?
b.) hdd on port 0 not in use?
what does this mean?
is this the reason why i do get he message about the “missing os system”?
because i can see the sda if i start a live-sytem and can also create a backup with clonezilla.
c.) is it a normal behaviour of RAID-1 not to boot if the mirror is broken?
should this behaviour be bein expected, or could it be also posible to boot a system even if the mirror is broken?
e.g. the mirror was broken a long time ago - but was not recongniced.
so the system was running in a “degraded” mode.
thank you for you help!
greetings lakk