I didn't say introducing the #3 server caused this - I just mentioned that after I added #3 to the pool a while back, it had a similar event. The first time it happened, I let it slide, waiting to see if it would do it again. Yesterday at 10am, it had the same type of problem (isolated itself and rebooted) so today I decided I'd better pull it so that it wouldn't do that during business hours. At the time it only had two VMs running on it, and they weren't at all taxing the system.
They are all identical systems - Dell R610's with the same CPUs, the only difference is that #3 uses 48GB of RAM while the other two are 96 GB. I even upgraded all of them to the exact same firmware revisions before putting them into production and after testing them. #3 is just a bad egg. Not sure what the problem is, but it's powered off right now and I'll take a look at it if I get time to this week.