You are right. However, the installer offers to first update the booted disk (green arrow) by default. One can only manually choose the other disk(s). Just updated Microsoft autoupdate and it did not even ask me where to go: updated the booted disk as well. Therefore, my impression that the installers do not install something "by mistake" and try the booted disk first still stands.
I'm saying: Some installers sometimes do the wrong thing.
You're saying: No, no. Sometimes the installer does the right thing.
I can't know, until I run one, what any particular installer is going to do. The safe course of action is to assume the worst, and take defensive measures.
Which, come to think about it, is what this thread is about. Sometimes, backing up a running system works. Sometimes it doesn't. I don't want my backups to work only sometimes.
