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You need a majority (MORE than half, not exactly half) of etcd available, so an even number is always bad. The 6th node is an extra piece of hardware that can fail but provides no extra failure tolerance. What you described will fail if EITHER location is unavailable, because NEITHER one has a quorum on their own. What you want isn't possible with 2 locations. You need 3 locations to be able to lose any 1. With 2 the best you can do is have a majority in one of the locations so that it still works if the other is unavailable (but not vice versa).

thanks @full-painter-23916, sadly we don't have 3 locations.

A third one could be one vm in AWS or something...