I never would have dreamed that my weekend can be such a nightmare. The official plan was to have a 3 hour downtime to upgrade the firmware on the switches. I said that's fine by me. I will have a visitor but for three hours that's okay.

After the upgrade the nightmare began: the cluster wasn't able to start again. Unfortunately, the distributor wasn't able to find the problem... at least until Sunday evening. So we had around 25h downtime of a productive cluster, my visitor had to look out in Stuttgart for himself and I had two days in the bureau where we just had to wait...

at least everything works fine again.