Your can do active-active in the data center, it's just not with warm spare mode. You could additionally have warm spares for each of the active nodes for redundancy. As I understand it, the argument against an active warm spar is that if you have two MXen worth of load, then you don't really have high availability. The moment one MX goes down, the other will choke and drop stuff. It sounds like the feature you really want is clustering, where N MXen can act as a single logical one. Active-active is just a lazy version that only supports 2 nodes.
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