Downtime today

The last weeks we've had some hangs, lasting upto and hour or two, which I still have now been able to track down. It could be related to the fact that we are using ZFS now. In an attempt to avoid the hangs, I upgraded the mother OS (on the physical server) today. Unfortunately it did not come up after a reboot, which happened during a busy day at work. It took some time before I could look at it and also to find out what was wrong. According to Nagios, we were down from 12:46 to 20:52. And yes, I do get an SMS message if the server goes down.