Okay this seems like a right thread to go to.
Game, this is bullshit. Unadulterated bullshit. I used to like reanimating terrifying embarks a lot for the way they force you to think. That everything, even your own dorfs, can suddenly end you if you relax just a bit. The real challenge, however, laid in maintaining FPS reasonable while eliminating swarms of undead and piles of junk inevitably covering the surface in thick layer. I was creative, I built cunning contraptions, and it was genuine DF fun. Then something seemed to change.
I was doing great, maintaining sizable population and pretty clean surface (meh, thank the lack of invaders for that) when FPS counter took a hit. I checked the readings and noticed the start of what I call the "undead plague" sweep. You see, in terrifying places cavern layers are your safe heaven with all you need to live and more. Cavern critters are well alive and don't bother you much. That is, until something hits something on the head too hard. Usually a runaway FB, a crundle. Which starts a powerful cascade of reanimations that sweeps through the entire cavern layer, turning it into an extra hell plagued with eternal combat reports. Ironically, the FB that caused this nonsense is usually among the first to join the undead ranks. My natural response to that is setting up extermination facilities to keep the numbers low. I rarely have enough forces to overtake the caverns entirely with how reanimation works.
I went about my usual business while FPS kept plummeting down. When it hit 15 it was all too late. Excruciatingly slowly built grinders immediately went out of order, the traps got overwhelmed, and I sent in the hammerlords as a last ditch effort. With a really curious result. An entire squad has failed to knock out *one single gorlak corpse* ten on one while loosing two men in the process, who I might add were wearing full iron with silver hammers.
I cringed and unfolded DFHack. This is not my way of doing things, but the situation was hilariously dire. A quick exterminate undead command yielded nothing. Like, literally nothing. The FPS upped from 6 to ~10 and that's it. Autodumping all ~1k+ crap assortment into the smasher did the same - Jack Didley. And that one made me put on my thinking cap after I abandoned.
So, the old hippie way of "you don't bother them they won't bother you" doesn't work anymore - the plague sweep starts without you. Cage traps eliminate undead slower than they multiply and drain your workforce a lot. Weapon traps are effective but tend to clog up on extreme numbers and drain your workforce a lot too. FBs outright ignore them, and those are *undead* FBs too. Not to mention I haven't tested weapon traps against new tougher undead. Head-on approach turned out absolutely horrible with everyone dying. Copper bolts seem to be bouncing off zombie crundles too, their damage got fixed recently (civil defence plan is ditched now). Smashers don't work either with the abundance of bigger creatures in lower caverns. Installing a "pre-mincer" just multiplied the threats - apparently a living blind cave ogre finger still breaks the bridge just as well as a whole ogre did. FBs again. Undead still don't burn in magma. Cheating doesn't work too.
So, to sum it up we have exponentially multiplying by themselves undead monsters that can't be smashed, trapped, burned, hammered or shot, that cause a permanent FPS drain even if you do. That seems like an overkill to me. Okay, I still haven't tried the two last options. Bum-rush cavern wall-off and cave-in traps. But where do I get enough workforce to make it work so fast?