RAID 1 issue - How to recover a broken disk - WD PR2100

One of my WD PR2100 disks is showing a solid red light.
I suppose I have to replace the disk with a new one?

My question is, the RAID modus is RAID 1, will the volume recover itself ?

Do I have only replace the disk or is there more to do ?
Is it absolutely necessarily (I know it is always better but I do not have the possibility) to make a backup first ?
Thanks for the support !

Just replace the disk „should“ be ok